The Ecology of Mugu Lagoon, California - USGS National Wetlands ...

Cover photos:Changes due to sedimentation in the central basin of Mugu igoon frni.ri 1971to 1983.

Biological Report 85(7.15)June 1987THE ECOLOGY OF MUGU LAGOOM, CALIFORNIA:AN ESTUARINE PROFILEChristopher P. OnufMarine Science InstituteUniversity of CaliforniaSanta Barbara, CA 93106Project OfficerEdward C. PendletonNational Wetlands Research CenterU.S. Fish and Wildlife Service1010 Gause BoulevardSl idell, LA 70458Performed forU.S. Department of the InteriorFi sh and Wi 1 dl i fe ServiceResearch and DevelopmentNational Wetlands Research CenterWashington, DC 20240

The mention of commercial product tradenames in this report does not constituteendorsement or recmmndation for use by the Fish and Wildlife Service, U.S. Departmentof the Interior.Onuf, Christopher P.The ecology of Mugu Lagoon, California.(Biological report ; 85 (7.15) 1"June 1987. "Bibliography: p.Supt. of Docs. no.: I 49.89/2:85(7.15)1. Estuarine ecol ogy--Cal i fornia--Mugu Lagoon.2. Lagoon ecol ogy--Ca7 ifornia--Mugu Lagoon.I. Pendleton, Edward C. 11, National Wetlands ResearchCenter (U.S.) 111. Series: Biological report(Washington, D.C.) ; 85-7.15.This report may be cited as:Onuf, C,P, 1987, The ecology of lvlugu Lagoon, Cal ifornia: an estuarine profile. U,S.fish Wildl, Serv. Biol. Rep. 85(7,15), 122 pp.

PREFACEMugu Lagoon is a tiny estuary. Xn anyother coastal region of the UnitedStates, it would have attracted littleatten tion, However, among the protectedshallow-water embayments of the arid andsteep Pacific Southwest, Mugu Lagoon islarge, important, and relatively fi ttledisturbed (because of protection by theU.S. Navy for more than 40 years). Consequently,the lagoon has received considerableattention over the last 20years, including intensive research onaspects of its geology and biology.Over this satne period, an awarenessgrew of how meager and in what jeopardywere the remaining estuarine resources ofthe region. With this growing awarenessof the need to protect, manage, and enhancethe remnants, the need to understandthe functioning of these ecosystemsbecame apparent. Accordingly, the endowmentof scientific information on MuguLagoon became valuable for management.This report is a synthesis of informationon Mugu Lagoon, supplemented byother sources as necessary to provide anintegrated treatment of ecosystem structureand function (Chapters 1-5).Although the analysis is most directlyrelevant to Mugu Lagoon, the rationalefor imch of the research and especiallyfor this synthesis was that the characterizationof this relatively heal thysystem would serve as a model and yardstickfor application to other, usuallymore highly modified coastal wetland ecosystemsin the region. Comparisons betweenthe we1 1 -functioning standard andother systems of concern should revealma1 function and suggest remedies (Chapter6) =Unfortunately, events of the lastdecade have a1 tered the "health"and little-disturbed state of the MuguLagoon ecosystem, Sedimentation caused bymajor storms virtual ly el iminated thelargest open-water area of the lagoon andcompletely a1 tered the bottom characteristicsof another major section of thelagoon. Protection of the lagoon, itsfringing marshes, and adjacent uplandswere ineffectual in shielding the systemfrom inputs originating in the fartherreaches of the watershed.This report chronicles how the impactsof those a1 terations ramified through theestuarine ecosystem. In retrospect, thiscase history of startling and profoundalterations occurring so suddenly may bemore instructive for management of theregion's embayments and their associatedwetlands than the original objective ofusing Mugu Lagoon as the "pristine" standardfor guiding management. Chapter 7presents some of these management considerations.The infonnation base for this synthesisis weak in some topical areas where thatfor the companion report in this series,"The Ecology of Tijuana Estuary: AnEstuarine Profile" by Joy Zedfer, isstrong. Reference to that source is encouraged,particularly regarding the anal -ysis of factors influencing primary productivity and salt marsh community structure.Comments concerning or requests for thispub1 ication should be addressed to:Information Transfer SpecialistNational Wetlands Research CenterU.S. Fish and Wildlife ServiceNASA-Sl idel 1 Computer Complex1010 Gause BoulevardS'l idel 1, U1 70458.

CONVEWSBQSIU TABLEMetric to U. S.CustomaryMultiplymillimeters (mm)centimeters (cm)meters (m)meters (m)ki lometers (km)kilometers (km)5 To Obtain0.03937 inches0.3937 i nches3.281 feet0.5468 fathoms0.6214 statute mi les0.5396 nautical mi lessquare meters (m2) 10.76square kilometers ( k1n2) 0.3861hectares (ha) 2.471square feetsquare milesacresliters (1)cubic meters (m3)cubic meters (m")mi 1 l i grams (mg)grams (g)ki 1 ograms (kg)metric tons (t)metric tons (t)kilocalories (kcal)Cel s i us degrees (OC)0.2642 gal lons35.31 cubic feet0.0008110 acre- feet0.00003521 ounces0.03527 ounces2.205 pounds2205.0 pounds1.102 short tons3.968 British thermal units1.8(0~) + 32 Fahrenheit degreesU. S. Customary to Metricinches 25.40 millimetersinches 2.54 centimetersfeet (f t) 0.3048 metersfathoms 1.829 metersstatute miles (mi) 1.609 kilometersnautical miles (nmi) 1.852 ki lometerssquare feet (ft2)square miles (mi2)acresgallons (gal)cubic feet (ft3)acre-f eetsquare meterssquare kilometershectares3.785 1 i ters0.02831 cubic meters1233.0 cubic metersounces (oz) 283.5 milligramsounces (oz) 28.35 gramspounds (lb) 0.4536 ki logramspounds (lb) .00045 metric tonsshort tons (ton) 0.9072 metric tonsBritish thermal units (Btu) 0.2520 ki localoriesFahrenheit degrees (OF) 0.5556 (OF - 32) Celsius degrees

PagePREFACE ......................................................................... iiiCONVERSIO!4 TABLE ..........................................................ivFIGURES ............................... ....................................... viiTABLES .......................................................................... xiACKNOWLEDGMENTS ................................................................. X i iCHAPTER 1 . INTRODUCTION: HISTORICAL PERSPECTIVE AND OVERVIEW .................. 11.1 Geologic History ............................................*....... 21.2 Recent History ...................................................... 4CHAPTER 2 . ENVIRONMENTAL SETTING ............................................ ... 82.1 Regional Geology and Characterization of the Watershed .............. 82.2 Clilnate ............................................................. 112.3 Hydrology ........................................................... 142.4 The Physicochemical Environment ..................................... 17CHAPTER 3 . PHYSIOGRAPHY ........................................................ 203.1 Structural Components . Before 1978 ................................. 203.2 Structural Coniponents . After 1978 .................................. 283.3 Major Stoms in 1978 and 1980 vs . 1962 and 1969: Differencesin Their Effects on the Eastern Am1 ....*.......*......,... ..... .*.... 32and M.L . Quammen) ................................................. 384.1 The Plants .*............................... ........................ 384.2 The Invertebrates ...................................., .... 474 , 3 The Fishes .......................................................... 544.4 The Birds ..................................................... ... 594.5 The Herpetofauna arld Flaiqinal s ........................................ 674.6 Sumrnary ............................................................. 67.. Quamrnenand C.P. Onuf) .............Primary Productivity ................................................The Availability of Prilnary I'rodtrction to Consumers .................Primary Consurttption ........................ . ...............Predation .......................................e... ...............Higher Trophic Levels ...............................................Nutrients ...........................,..........,..a.*ee.eeee...a**................................................An Ecological OverviewCHAPTER 4 . THE BIOTA: DISTRIBllTION AND ABUNDANCE (by C.P. OnufCHAPTER 5 . THE BIOTA: DYNAMICS AN[) INT'FKACTIONS (by F1.1

CHAPTER 6 . COMPARISONS ......................................................... 936.1 Geographic Variation in Coastal Climate and Topography .............. 936.2 Comparison of Mugu Lagoon to the Other SouthernCalifornia Estuaries ................................................ 96CHAPTER 7 . MANAGEMENT CONSIDERATIONS ........................................... 1037.1 Protection..* ........................................................ 1037.2 Sedimentation .................... .................................. 1047.3 Other Water-Borne Contaminants ...................................... 1077.4 Alteration of Tidal Flushing ........................................ 1077.5 Endangered Species .................. .* ...................... 1107.6 Information Gaps .................................................... 114REFERENCES ...................................................................... 117

1 Major structtrral features of southern California ........................ 32 Extent of %gu Lagoon sediments ,..,,.....,......r...................r. 53 Geological !nap of the watershed of Mugtr Lagoon .......................... 94 Characteristics of the Mugu Lagoon watershed: (a) sui tabil i tyof soils for agriculture, (b) natural vegetation, and(c) agricultural crops ...................... .......... . ......... 105 Characteristics of the climate of Mugu Lagoon: (a) air temperature,(b) precipitation, and (c) number of years with different amountsof precipitation ........................................................ 126 Wet and dry periods in southern California .................... ...... 14iStreanlflow in Calleguas Crcek: (a) mean flow in different inonths1969-77, 1978, and 1980, and (b) man flow by day in 1980 ............... 158 Tidal curves for several days in June and July 1981 ..................... 169 Meandailysolarradiationandskycover ............................... 1910 The main physiographic and land-use features of Mugu Lagoon ............. 22IIVariation in substrate texture with depth frorn a core takenin the eastern pond of the eastern am, Mugu Latjoon ..................... 2312 %ration of rnaximum tidal exposure and subtnersion forMission Bay Marsh ..................................................... 2513 Sediment triangle and map showing sa!rtples in which silts wererelatively enriched in surface sedirnent samples in theeastern arm of hgu Lagoon ,. . 26........................... .......14 Extent of intertidal f7ats in the central bdsin of Muyu Lagoonin different years ....................... .......................... 2815 Sedirnent texture before, during, and after the major seriesof storms in 1978 ....................................................... 3016 Sedirnent-sampling sit@.; and nrPas of t h lagoon ~ with ~iinilgrsediment changes in response to the ii~~ajorstom of Fehruary 1978 ........ 30

Number17 Changes in surface-sediment texture at sites in the tidalchannel and western pond of the eastern am, HU~U Lagoon . .*@.18 Changes in depth of the eastern arm of Mugu Lagoon caused primarilyby the storms of February 1978 and 1980 .... *.. . . O . . .*. ...*, .. .ee. . .. . . . . . . . 30.* I 3119 Relationship of the eastern arm of Mugu Lagoon to inputs fromCal feguas Creek under different tidal conditions . . . . . . . . . . . . . . , . . . , e.. 3320 Cumulative deviations from the long-term mean precipitation(34-year record) at Point Mugu, California ..., ........,,,,... .... . 3421 Hil 1 side development near Moorpark, California, 1979 . . . . . . . , , . , .. . . . . . .. 3422 Extent of hi1 lside development in one part of the watershedof Mugu Lagoon at different times .....,......,....,.........,~,e...I),.~t 3523 Areas with high rates of accelerated and geologic erosion ....,.,.....,.. 3624 Changes in pigment concentration and composition from June 1977to June 1978 ................................................. 4025 Dominant plant of the salt marsh, perennial pickleweed (Sal icorniavi rginica) ............,,. .,.,............... *.. .... . . . 4326 Biomass of Sal icornia vi rginica in the lower marsh at Mugu Lagoonin different months . . .. .... .. ...... *. . . ".. . ... . . . ..... 4327 Biomass of Saf icornia virginica vs. distance from the lower edgeof the marsh ............................................... . . 4328 Illustration of the years x location interaction on the biomass ofSal icornia virginica in the lower marsh at Mugu Lagoon . . . .. , , , . ., . . . . . . . 4429 Biomass of common plants of the upper marsh at Mugu Lagoonin different months, 1977 . . . . . , . . . . . . . . . , . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . 4530 Changes in the biomass of the common plants of the uppermarsh at Mugu Lagoon, 1977-81 ...........,............................... 4631 Changes in mean biomass of salt marsh plants in the uppermarsh compared to the lower marsh, 1977-81 . ... . . . .. . .. ..+. . * .. 4632 Locations sampled quarterly for invertebrates in the eastern amof Wgu Lagoon in 1977, sites grouped according to 50% similarityin densities of major categories, and mean densities of thosecategories in each group ............................ * ........ . ......... 4833 Changes in densities of invertebrates from 1977 to 1980 .......... ,..,... 5234 ~ish-sampling sites and their characteristics in 1977 . .... . . . . . , , . . . . .. . 5535 The S-year average monthly fish catch at M I J ~ Lagoon, ~ arrangedby month of peak abundance ... . . . . . ..,,. . . . . . *. . . . . . . . 58

Chartges in i?jean rnonti?ly fish catch and mean number of speciescaught, 1977-81 .........................................................Characteristics of satnpling sites and the locations where differentspecjes of fish were 120s t cariunonly caught in 1977 and 1981 ..............Five-year average abundances of water-related birds by month atcensus sites 1-20, Mugu Lagoon ....,.....................e.eIe(.e.e.*....*.i3ird census sites grouped according to > 60% similarity in theirdensities of the indi caeed categories of water-re1 ated hi rds andthe iriean densities (no./ha) of each category in the differentgroups of sites .........................................................Changes in bird abundance over time at Mugu Lagoon ......................-%-Density of shoots 07 Salicornia vir inica in the lower marsh ofMugu Lagoon a1 ive addifferent tlmes urlng the growing seasonand accumulated deed since January ....................... ..........*Contributions of different sources to the total net primaryproductivity of the eastern arm of Mugu Lagoon ..............*..........neco~nposi tion in water of macrophytes in southern Cal i forniacoastal wetlands ..............,...............................e..*......Stratification in the depth of living position of the abundantshe1 led invertebrates in different habitats of Mugu Lagoon ..............Abundances of wonns, surface-feeding shorebi rds, and crabs andwil lets through the course of a year at two locations varyl'ngin the sand content of the substrate ....................................Plankton samples collected in the eastern ann of Mugu Lagoon atapproximately hourly intervals on 7-8 August 1978 .......................Monthly changes in fish abundances in the eastern ann of Mugu Lagoonafter the inonth of peak abundance for five of the common specjes........Pacific coast of North herica from 30" to 50°N, Physical relief;normal rnonthly total precipitation, mean rnonthly river discharge and meanannual total precipitation; growing season; mean daily solar radi at1 on;dnd mean annual pan evaporation .........................................Large estuaries of southern California: Mugu Lagoon, Ti juanaEstuary, Upper Newport Bay, Anaheim Bay .................................Primary productivity as measured by August biomass of the lowermarshes at Tijuana Estuary and Mugu Lagoon,.......... ....................Smal ler estuaries of southern Cal ifornia: Agua Hedi onda,Up~er Bolsa Bay, Carpinteria Slough, Goleta Slough, LosPenasquitos Lagoon ......................................................Topographic maps of Mugu Lagoon in 1980 and as projected in 2030 ........Page

Number53 Two a1 ternatives for channel ization of Cal leguas Greek proposedby the U.S. Amy Corps of Engineers Los Angeles District in I972 ........ 10854 California least tern ............................ee.m*..C*.e ..me.......e ill55 Salt marsh bird's beak .................................................. 11256 Light-footed clapper rail .................... . ........................ 11257 Be1 di ng 's Savannah sparrow .................... ..................... 113

TABLES,ll ternation of marine and terrestrial fonilations in thestratigraphic sequence of the watershed of Mugu Lagoon .................. 4Structural components of the Mugu Lagoon estuarine ecosystem ............ 27Relative i~nportancc of different categories of plants in thedi ffererlt hdbi tats of tile Mugu Lagoon estuarine ecosystem ............... 39Mean density of inv~rtebrates in 1977 for a11 sites sampled in theeastern am1 of Mugti Lagoon ....................... .. . ................ 49Total catch of fishes by species and site in the 9 months of 1977whtln a1 l sites werc san~pl ed .........*............. .. . .. .,... ... 56tiabitat characteristics of the cornlnon species of fishes in Mugu Lagooninferred from features of the sites at which they were caught mostfrequently .............................................................. 57Abundance ranking and mean nuiriber of birds seen per census averagedover all sedsons for 21 census sites in Nugu Lagoon ..................... 61Primary productivi ty in Mugu Lagoon: estimates of annual productivityfar different sources, conditions to which estimates apply, andconversions to siriiilar units ................... ........... ...... . 71Factors reducing the utilization of a source of primary productionby ~:~acroconsumers within the Mugu Lagoon estuarine ecosystem ............ 75Gut contents of fishes in Mugu Lagoon, February 1977-January 1978,a11 stations and rr~onths combined ................... . ................... 84Utilization of the eastern anri of Mugu Lagoon by the 10 mast cornmonlycaught fish species in 5 years of sal-ipl ing ., .eLe* 89Mean densities of the common she1 1 ed inacrainvertebrates and thei rpercent total density in subtidal sandy areas of Mugu Lagoon andTijuana Estuary ......................................................... 99Ranking of abundances of common fish species in four large southernCalifornia coastal wetlands .....,..................................I).... 100

ACKNOWLEDGMENTSI am grateful to the many people whosehelp made this monograph possible. Myfirst debt of gratitude is to my colleaguesBob Holmes and Pete Peterson forgetting me started in Mugu Lagoon. Nysecond debt of gratitude is to my twoprincipal coworkers, Mil 1 icent Quammenand Gary Shaffer, whose unstinti ngefforts and close cooperation helped melearn most of what I know about MuguLagoon. Most of our studies were onlypossible because of the assistance ofmany students in the field and laboratory.I benefited fran c1 ose contact with JoyZedler, Wayne Ferren, and Eric Metz for abroader perspective on southern Californiacoastal wetlands. Much of theresearch on which this synthesis re1 ieswas supported by the California Sea GrantCol lege Program. I thank the Commander,U.S. Naval Air Station, Point Mugu, forthe opportunity to conduct research inMugu Lagoon and Base Biologist Ron Dowfor his cooperation. I a1 so benefitedfrom the outstanding human and materi a1resources of the Library, University ofCalifornia, Santa Barbara, especial lyGovernment Publications and the Map andImagery Laboratory. The comments of technicalreviewers, including KeithMacdonal d, Pete Peterson, and Joy Zedler,helped me improve the report and I thankthem. Reviews by the U.S. Fish and WildlifeService Field Office, Laguna Niguel,California, and the Natural Resources ManagementOffice at Naval Air Station, PointMugu, he1 ped el iminate errors. JunePhinney typed and retyped the manuscriptspeedily, cheerfully, and we1 1 , for whichI thank her. Penny Herring, SueLauritzen, Kate Lyster,the National Wetlandsand Rob Brown ofResearch Centerexpertly assisted with production. Withoutthe assistance of Ed Pendleton asreviewer, arbiter, and emissary of good-I under trying circumstances, therewould be no report.I dedicate the report to MillicentQuammen, where her indispensable contributionsare not acknowledged by authorship,and Nathaniel Onuf, for the timestolen from him to complete this largetask.

West tidal creeks, looking east, at Mugu Mudflats with foraging shorebirds (photoLagoon (photo by R. Dow), by Mil 1 icent Quammen) .Central Basin of Mugu Lagoon (photo by Central and east anns of Mugu Lagoon8, Dow), (photo by R. Dow).East Am, law tide, burrows of Callianassa East arm of Mugu Lagoon at high tidecal iforniensjs (photo by R, Dow). (photo by R. Dow).xiv

CHAPTER I. iNTRODUCTiON:HlS'trORliCAh PERSPECTIVE AND OVERVIEWEstuaries are not estuaries most of thetime in the Pacific Southwest of theUnited States. The little rain thatfalls is confined to one-half of theyear, during which the average monthlyevaporation exceeds average monthlyprecipitation in all months at coastalpoints (U.S. Environmental Data andInformation Service 1980).When the effects of transpiration ofwater back into the atmosphere by thevegetation are included, the deficit innear-su rface water is magnified. Inaddition, the watersheds are small andsteep, but the mountains that delimitthem landward are not high enough toretain snow for long. Consequently,1 ittle water concentrates or is stored ator near the surface. Therefore, coastalstreams and even rivers are intermittentor seasonal, as are the flows intocoastal embayments.Human activities have tended to furtherreduce the amount and duration of freshwaterinputs. Natural waterways arecircumvented by damming, distributing thewaters to human dwel lings, recol lectingthose waters, now laden with wastes, anddumping them directly into the ocean.Because the burgeoning human populationhas encroached into natural floodways,southern California has become "the landof the paved river" to insure thatsurface water does not tarry long whereit might damage nanmade structures. Thenet result is that little becomes lessand even more limited in duration.Hence, my assertion that these estuariesare not estuaries most of the time,follows Donald Pri tchard's introductorydefinition in the herican Assocjationfor the Advancement of Science (AAAS)symposium volume Estuaries, pub1 ished in1967: "An estuary is a semi-enclosedcoastal body of water which has a freeconnection with the open sea and withinwhich seawater is measurably dilutedwith freshwater derived from land drainage."In the land of estuaries that are notestuaries most of the time, perhaps it isa1 together fitting that the first subjectfor an estuarine profile was not an estuaryin any sense until 1884, when itbecame so by the hand of man. (Steffen1982). Echoing Joy Zedler's often repeatedtheme in her community profile on"The Ecology of Southern Cal iforniaCoastal Salt Marshes," no aspect of thefunctioning or present character of thisregion? estuaries can be pursued veryfar without reckoning with the effects ofpast, present and future human activities,both within and surround1 ng theembayments.One other characteristic of these intermittentestuaries of the PacificSouthwest interacts with the justmentionedfeatures of c1 imate and recenthi story to set these wet? and ecosystemsapart from their counterparts in othercoastal regions of the United States.Because the coast has been upliftedso recently, it is steep. As aresult, these areas of shallow coastalwater protected from the violent waveaction of the open coast are few, small,and separated from one another by Songstretches of very different shore environments--usual1y narrow sand or rockplatform beaches backed by cliffs.In net, estuaries, intermittent orotherwise, have heen, hjstorjcaTly rare inthe region, Rapid development by humanshas made these environments even rarer

and has degraded many surviving areas,Nevertheless, as el sewhere, the cmhinationof protection from violent wsveaction, shall ow water, ample sun1 igRt(even to the bottom of subtidal areas),regular tidal exchange, and equable climateyield an abundant and varied bioticenvironment, Not surprisingly, someorganisms have come to depend an theseproductive coastal areas : as necessarystopping places and overwintering areasfor several migratory bird species thatuse the Pacific Flyway, possibly as theonly nursery ground for at least onecommercially important fish stock (seeChapter 51, and as the only habitat forthree species now classified as endangered.Thus, rarity is a major ingredientof the significance of coastalwetlands in southern California (Onuf eta1. 19791, and concern about continuinglosses and degradation is urgent.Urgent concern, coupled with the severaldistinctive characteristics sharedamong southwestern intermittent estuariesbut distinguishing them from the estuariesof the other regions, prompted thecompilation of an estuarine profile forsouthern Cal i fornia. Mugu Lagoon waschosen for a variety of reasons, of whichI list three. hang the few, in somecases forlorn, remaining wetlands insouthern Cal ifornia, Mugu Lagoon is noteworthyfor its (I) relatively large sizeand (2) its freedom from many of thehuman incursions that afflict other areas(because the lagoon and its surroundingsalt marsh lie within the fenced andpatrol led boundary of a mi 1 i tary reservation).Consequently, there was somereason to be1 ieve that a wide range ofcoastal wetland habitats was representedat Mugu Lagoon in natural relations toone another; i.e., Mugu Lagoon provid~d aglimpse of &at these systems could belike when free of undue human intervention.Perhaps, then, Mugu Lagoon couldserve as a model for undoing damage toother wetlands. This was my reason forconducting research in Mugu Lagoon. Thesecurity provided by the Navy also was aninducement, to carry out long-term observationsand experiments that could nothave been contemplated where access wasnot strictly controlled, As a result,(3) more detailed scientific research hasbeen performed at Mugu Lagoon than anyother coastal wetland area in southernCaf i frsrnia, although coverage of differerlttopics is very uneve~,1.1 GEOLOGIC HISTORL'There must be an element of arbitrarinessin the decision of when to begin thehistory of a place, particularly for onesuch as Mugu Lagoon, perched on the edgeof an actively moving continental plate,Because of this precarious location, theregion is incredibly active tectonical I y,What is here now bears little relation toeven its recent antecedents.The region is very active. The streamthat empties into the lagoon originatesin the wild jumble of the TransverseRanges (oriented east-west or transverseto the north-south trend of the majorranges of California, the Sierra Nevadaand the Coast Range) only 50 km from theSan Andreas Fault (Figure 1). Along thefault, instantaneous rates of 1 ateraldisplacement of 6.4 m and 3.0 m wereidentified with the San Francisco earthquakeof 1906 and the Imperial Valleyearthquake of 1940, respectively (Hill1954). Within the Transverse Ranges,only 25 km from the boundary of thelagoon's watershed, a 0.9-m vertical di s-placement occurred along a thrust faultduring the San Fernando earthquake of1971. The estimated average rate ofuplift along the thrust faults of theregion is 8 m per 1,000 years (1 cm in1.25 year). In sme locations rates arebound to be much higher (Scott andWilliams 1978). In summary, quoting fromScott and Williams: "Deposits of latePleistocene age are in a steeply inclinedattitude at many localities in the area,and are actually overturned at several -to within 50" of complete overturn inOrcutt Canyon, a study watershed. Infact, the structural deformation of depositsof the youngest geological timeperiod in the Transverse Ranges is withoutknown parallel in North America."Even though very recent processes arealmost exclusively responsible for thepresent physiographic character of therecion, the kind of material exposed bytectonic processes and weathering also isimportant. It is the parent material of

Santa Barbara Channel IslandsFigure 1. Major structural features of southern California. Upper relief mapshows the relationship of the Transverse Ranges to the other major mountainranges of southern California. Lower map shows the watershed of Wugu Lagoonin relation to major fault systems (adapted from Hi1 1 1954).3

the soils and fnfluences their fertilityand erodibility, Therefore, I begin thehistory of Mugu Lagoon in the Upper Cretaceous,approximately 100 mil lion yearsago, when the oldest rocks now exposed inthe watershed were laid down. The locationon an active continental margin isattested by the alternation of marine(deep, transgressive, and nearshore) andterrestrial deposits in the stratigraphicrecord (Table 1). A11 rocks are sedimentary,with the exception of one convulsionof volcanic activity in the Miocene.These volcanic rocks are exposed in thesoutheastern part of the watershed butapparently underlie more recent depositseverywhere else in the region, judgingfrom samples extracted during welldrilling (She1 ton 1954). Parenthetically,it is the Miocene sedimentarydeposits that have excited the greatestinterest local ly. They are consideredto be the source rocks for petroleum reservesin the Ventura area (Steffen1982).Accordi ng to Steffen's recent summary,the features that eventually defined thelagoon itself have been developing onlyTable 1. The a1 ternation of marine andterrestrial formations in the stratigraphicsequence of the watershed of MuguLagoon. Adapted from Steffen (1982).in the last 300,000 years, since theMiddle Pleistocene, Flood deposits fromthe Santa Clara River built up the OxnardPlain at the rate of 2 rn per century,until uplift at the end of the MiddlePleistocene directed the river to thenorthwest. At around the same time, thesoutheast portion of the plain subsided.Sea level reached its lowest stand about18,000 years ago and then rose to 2 mabove present level s approximately 3,000years ago. This was when the lagoon firstformed. Where littoral drift from thenorthwest (Bascom 1980) encountered thePoint Mugu headland, sand accreted, and amuch broader beach or spit formed on theupcurrent side of the obstruction. As thesea level dropped, the spit migratedseaward with it, and the enclosed coastalembayment has become the Mugu LagoonEstuary.Evidence for this process has cmefrm Warme (1971), who identified ridgesof sand within the salt marsh that fringesthe eastern arm of Mugu Lagoon. He interpretedthe ridges as relict beach bermsthat had formed during a higher stand ofthe sea. Apparently, the drop in sealevel was stepwise rather than continuous.If it had been continuous, it would behard to account for the water-filledtrough (the lagoon) that lies between thecurrent and past berms, rather than dunesor a wall of sand such as climbs the flankof the headland 5 km to the southeast.Years before Geological Depositionalpresent age envi ronmen tCenozoic:600,000 Pleistocene Terrestrial10,000,000 Pl iocene Deep marine25,000,000 Miocene Transgressivemarine35,000,000 01 igocene Terrestri a155,000,000 EocenemarineNears hore65,000,000 Paleocene Nears horemarineMesozoic:100,000,OOQ Upper Creta- Terrestriala Coarse particf es deposited in shallowwater and fine particles in deep water.1.2 RECENT HISTORYMugu Lagoon has a water area of approximately130 ha. Judging from the distributionof recent lagoonal depositsoverlying deltaic deposits, it was tentimes that size at its largest (Figure 2).Presumably, this was soon after the originof the lagoon when the sea level was 2 mhigher. The lagoon is elongate, runningpara1 lel to the coast for 5.6 km but neverexceeding 1km transversely. It iscomposed of two long arms projecting outfrom a broader central basin. CalleguasCreek, the only inlet stream, dischargesinto the central basin. The mouth of thelagoon usually opens in the vicinity ofthe central basin, but it has been knownto migrate 0.75 km eastward. The eastern

Figure 2. Extent of Mugti Lagoon sediments (fran Steffen 1982, based on a geologic mapin California Division of Miires and Geology, Preliminary Report 14, 1973).ann is very narrow because the shore issteep along the flank of the Santa MonicaMountains. The western arm is broaderand has a wider expanse of fringing saltmarsh, because in this direction thelagoon extends into the Oxnard Plain.Human occupation of the area aroundMugu Lagoon probably began around 7,000years ago (Macdonald 1976a). The coastalstrip along the Santa Barbara Channelsupported one of the densest aboriginalpopulations in what is now the UnitedStates--which is surprising, consideringthat the California Indians were huntergatherersand not agricul tu ral i sts(Hornbeck 1983). The Chucnash village onMugu Lagoon at the time of Europeancontact (1760) was estimated to have 400inhabitants, but densities dropped offrapidly inland (Hornbeck 1983). The highlocal density of hunter-gatherers indicatesthat the Indians could have had alarge effect on populations of fishes andthe larger invertebrates in Mugu Lagoonand game in the surrounding uplands,while effects on the watershed would beminimal, During the period of theSpanish missions and Spanish dnd Mexicanranchos (1782 to 18451, agricu! ture wasintroduced. A1 though mission recordsshow that substantial amounts of wheatwere harvested in the Ventura area(Hornbeck 1983), the main agriculturalactivity in the watershed of Mugu Lagoonwas grazing cattle (Murphy 1979). Presumably,some changes in the naturalvegetation resulted, but the character ofthe landscape probably did not change.Soon after Mexican control was supplantedin the region (1846), "Anglo"settlers began to intensively cultivatelarge areas of the watershed of MuguLagoon. Between 1876 and 1881 railroadconnections with San Francisco and theeastern United States were established,and agriculture became a big exportbusiness (Steffen 1982). Shortly aftercrop agricul tu re became establ i shed onthe Oxnard Plain, Calleguas Creek waschannelized, and its flows were shuntedinto the lagoon. As already indicated,Mugu Lagoon has been a true lagoon ratherthan an estuary for most of its existence.In 1884 Mugu Lagoon became anestuary.Before the channelization of the creek,there were no significant terrigenousinputs to the lagoon. Conditions probablyapproximated those of a coastalmarine mbayment. Undoubtedly, largeareas of the Oxnard Plain contiguous to

the lagoon were freshwater marshes duringthe rainy season, but their flows intothe lagoctn would have been sinaf I ccmparedto that of a channelized Calleguas Creek.The original watershed of the SantaMonica Mountains draining into the lagoonwas little more than twice the water areaof the lagoon itself and less than thearea of the lagoon plus its fringing saltmarsh. Consequently, interactions withthe ocean, sunlight, and temperaturewould have been the physical drivingforces rather than freshwater inflow.The tidal prism (volume of lagoon waterexchanged over a tidal cycle) would havebeen sufficient to keep the mouth open ata1 1 times, Regular tidal flushingcoup1 ed with shall ow depths would haveascured good exchange of materials withinthe lagoon; however, the mouth of thelagoon is at the head of a submarinecanyon, and the Continental Shelf isnarrow in any case, Therefore, the waterentering the lagoon often is relativelynutrient-poor, oceanic-blue water. Inthe absence of terrestrial runoff, thismay have resulted in lower primary productionthan is characteristic of rnostshal low-wa ter marine systerns. Nevertheless,the combination of shallow waterprotected from violent wave action, amplesun1 ight, higher summer water temperaturesthan offshore, and good tidalexchange must have made for an abundantand productive biota (as is attested bythe shell middens on the shore of the1 agoon).The rnajor human influence on MuguLagoon has been the funneling of dischargesfrom a watershed of 843 km2 into areceiving body less than 13500th thatsize, which previously had been subjectonly to marine influences. The repercussionsof that single alteration will betouched on throughout the rest of thisreport, Although the alteration was asingle discrete event, its effect cangrow, and a1 mos t certainly has grown.The channelized creek is a conduit. Itwill transmit whatever is put in alongits length to its lower end. As morepeople occupy the watershed or use itmore intensively, the inputs to the creekwill be a1 tered, In 1880, 4 years beforeNugu Lagoon became art estuary, the poplifationof Ventura County was 5,073. Thepopulation has more than doubled in every20-year period since then and in 198U was529,174, or more than iOO times greaterthan a century ago, Between 197@ and1980 the pspu2ation within the watershedincreased by 56% from 154,465 to 240,432,The cause and effect re? ationship betweenthe number of people and the amountof material that has potential impact ifit is carried into an estuary is notstraightforward. For instance, populationgrowth in this region could have thebeneficial effect of increased diversionof water to pathways that do not lead intothe estuary. Instead, the effect ofgreater significance is as follows: Thebottomlands have been under cu1 ti vat ionfor a long time. The growth of the populationin this area takes the form ofurbanization of these bottomlands. Ifthe process were strictly the substi tutionof a different land use on the samespot, the net result might well be lessinput to the natural drainage system.However, displacement rather than substitutionhas occurred. Rather than beingel iminated, intensive agriculture hasmoved up the sides of steep hills, theresubstituting groves of fruit trees withbare soil between the trees for grazedchaparral. This type of cultivationincreases runoff, possibly with substantialloads of agricultural chemicals, andaggravates soil erosion.Another consequence of the preemptionof prime agricultural bottomlands is thatthe large remaining acreage is farmedeven more intensively. The averagefrost-free period is 332 days. Customarily,three to four crops are grown eachyear in the Oxnard Plain area (Steffen1982), and some of thm are heavilydosed with chemicals. The strawberryfields, for instance, are covered withplastic so that the soil can be fumigatedfor nematodes, weed seed, and fungibefore each planting. An average of193.1 lb per acre (213-9 kg per ha) ofrestricted fumigant pesticides (almostexcl usivel y methyl bromide and chl orpicrin)is applied each year. In 1976,almost 800,000 Ib (360,000 kg) of pesticideswere applied in Ventura County(Gal i forni a Department sf Food and Agrictrftlire1378), the great majority wfthirrthe watershed sf Mugu Lagoon. A1 thoughfigures for fertilizers or, more

inportantly, levels of pestici;dtl resfduesor nutrients in agricultural drain watersare few, the potents'al for substantialinputs to Calleguas Greek and Mugu Lagoonobviously is high.Mot a1 l effects of development by humansare transmitted to the lagoon viaits inlet stream. The lagoon lies withinthe boundaries of the U.S. Naval AirStation at Point Mugu, Cal ifornia,(established in 1946), and the operationalpart of the base is built on filldredged from the central basin. Pastactivities within the lagoon itself,especially those associated with the constructionof the base, have led tolarge losses of wetland habitat and othermodifications that have altered ecosystemfunction. However, natural resourcesincontestably benefit from the militarypresence in other regards. The relativelylarge part of Mugu Lagoon thatremains a wetland has been left asnatural as possible, given the modificationsof its surroundings. The protectionbegan as a byproduct of naval securityand air clearance space requirementsbut now is an actively pursued policy ofthe Navy. As a result, the site has beensomething of a mecca for scientific studyfor many years.The current situation and probablenear-tern trends, then, are these: Thewatershed is dominated by agriculture;however, a burgeoning urban-suburbanpopulation has led to changes in agricul-tural practices that almost certainlyincrease the inputs of sediments andchemicals to the lagoon. The limitedavailability of freshwater locally andthe probable increase in water conservationand wastewater reclamation may we1 lreduce future inputs of stream water andwhat it carries during most of the year,but storm flows still will deliver sedimentsto the lagoon, sometimes in greatgluts. The consequences of this sedimentationwill be explored at length inother sections of this report.So far in this overview of Mugu Lagoon,the "estuary" has been treated as aunit--initially a very small one,essentially without a watershed, and nowa much bigger one, with concomitantlylarger terrigenous inputs. Every effortwill be made to encompass the wholesystem; however, there are major constraints.Inevitably, coverage isuneven. Some topics (most notablyassociated with the she1 led invertebrates)have been we11 studied, whileothers (most glaringly, nutrientchemistry) have not been investigated.Furthermore, almost all of the ecologicalresearch that has been carried out inMugu Lagoon has been in the eastern amof the lagoon, which is maintained by theNavy as an ecological reserve. Thislimitation in spatial coverage should beborne in mind throughout. Wheneverappropriate, the discussion w i l l beextended to include the other parts ofthe lagoon.

General ly speaking, average condi tionsprovide the most informative and mostoften utilized summary of what a systemis like and how it is likely to behave.However, It w i l l become abundantly obviousthat extreme conditions play a rolein Mugu Lagoon that is vastly more importantthan their frequency would suggest.The main thrust of this section will be,then, to ill ustrate how important departuresfrom average conditions are indetermining the characteristics of thisestuary and probably most others in theregion, Later chapters will show how theterrestrial part of this estuarine ecosystemexerts its influence over theestuary through the supply of sediments.Therefore, many of the topics of thischapter will be developed as they re1 atelater to the production or transport ofsediments to the lagoon.2.1 REGIONAL GEOLOGY AND CHARACTERlZATlON OF THE WATERSHEDThe watershed around Mugu Lagoon isnotable for its high erosion potential,Erosion is a leveling process. It is thepredominating force in determining thesurface characteristics of most 1 andmasses. Slopes are determined primarilyby the rates of weathering of the parentsocks and the length of time that erosionhas been working an ti~~,n. As erusionproceeds, slopes become more gradual,thereby slowing the rate of subsequenterosion. t4awever, in parts of the TransverseRanges of California, includingmuch of the watershed of Mugu Lagoon,this is not the case, The rates ofuplift substantially exceed the rates ofdenudation. The great tectonic activitythat now prevails, and has prevailed forat least the last ICO milfioc years, hasproduced a very yotrthful iarldscape.About 46% of the watershed tdis covered by1 ate Pleistocene or more recent a1 1 uvi a1deposits (Figure 3). These dominate theflat valley bottoms. The older rockshave been thrust up along faults andfolded into ranges of hi1 1s and mountains,Elevations are moderate (under1,200 m), but slopes are considerablysteeper than they would be in the absenceof ongoing uplift. Thus, past erosionhas not yielded a reduction in slope thatlessens present erosion, and the measuredrates of denudation "approach the maximumfor areas in which consolidated bedrockis being eroded directly" (Scott andWilliams 1978). Scott and Williams alsostated that the failure of standardmodels to include this factor of tectonicactivity accounts for their gross underestimatesof sediment yield in thisregion.The mineral canposi tion and structureof the rocks in this region also contributeto very high sediment yields. Thedivisions of rock types in Figure 3 weremade to correspond to the categories usedby Andre and Anderson (1961) in theirtests of soil erodibility with respect toparent material. According to their preferredindex of erodibility (surfaceaggregationratio), soils from Quaternarya1 luvium and acid igneous rocks were themost erodible soils that they tested.These soils cover 59% of the watershed.The Miocene vo1 cani cs and Quaternarya1 luviuin and terrace deposits of theTransverse Ranges were approxiinatelytwice as erodible as the consolidatedscdirnentary rocks (Scott and Hilliams1975) ; however, this factor was minorcompared to the effect of tectonicactivity on erosion.The juxtaposition of active mountainbuiiding next to a coastal plairl has produced:oils ranging from a thin veneer tomore than 1-5 m deep. Soils range from

Figure 3. Geological map of the watershed of Mugu Lagoon. Wi thin the watershed, rocksare grouped according to the categories of Andre and Anderson (1961): hard sedimentarydeposits (Cretaceous, Pal eocene, and Eocene marine shal e, sands tone, and conglomerate,and nonmarine 01 igocene); soft sedimentary deposits (Miocene, Pliocene, and lowerPleistocene marine deposits) ; igneous rocks of Miocene age; and a1 luvium (Quaternarya1 luvial and terrace deposits, mainly nonmarine). (Adapted from Jahns 1954.)prime agricultural land to land completelyunsuitable for cultivation, withuse restricted to the maintenance ofwildlife and watershed, according to theSoil Conservation Service's capabil i tyclassification. As one might expect fromthe discussion of geological factors, thethin soils that are unsuitable for agricu1ture invariably are associated wi thsteep slopes, and the prime soils are allin the valley bottoms (Figure 4a).Coastal sage and foothill woodland withislands of oak savanna are the dominantnatural communities (Figure 4b). Theyare not closely linked to soil type orcapability class. Agricultural uses ofthe watershed (Figure 4c) are dominatedby vegetable crops on prime agriculturalland of the coastal plain; fruit/nutcrops in the lower reaches of the val-leys, both on prime bottcxnland and marginalvalley sides; field crops in theupper reaches of valleys, mostly on soilswith severe limitations for cultivation;and grazing in the rugged hi1 1s. Nurseryoperations are interspersed throughoutthe vegetable and frui t/nut growingareas. Soils of high fertility areinterspersed in most soil types andcapability classes (California Departmentof Food and Agriculture 1978). Apparently,in this region of obSigatoryirrigation, factors other than fertilitydetermine the suitability of a soil foragriculture.The effect of vegetative cover and landuse on erosion is we71 known in principlebut less we17 known in actual applicationto this region. Throughout the watershedthe natural vegetation can be sparse and

'(8~61 a ~ n 2 ~ n 3 pup ~ ~ pooj 6 ~ JO Jua~~edag elu-JOJ~LP~ UOJJ pa~depe) sdolc3 le~nq~napG~ (2) put? $uo[?e~afjan te.inqeu (q) %~n?~n3&~6edo$ silos 40 IC2!.1kqe?!ns (e) :paysula%eM uoofjq n6n~ aql jo s ~ ~ ~ s y a p'gt slnE!j ? ~ ~ ~ ~

siopes can be precipitous; tnerefore, thethousands-fold di fferences in ?OSSshown -in early Sofl Conservation Servicetests between plots of siniilar area andslope with natural vegetation cmpared toplanted and hare crop land probably donot apply to these areas. idev~rtheless,the effect of land clearing on erosion isveq large. For instance, i:ieasurerner~tsof sediment yield in the western TransverseQanges of Ventura County were 11.9to 35 tirnes higher immediately after thetotal burn of watersheds than after 10years of regrowth (Scott and Williams1978). The effects of agriculture havenot been addressed explicitly in thecontext of local condi ti ons ; however,Steffen ( 1982) mapped areas of higherosion rates (greater than 10 tons peracre per year or 20 metric tons per haper year) and estimated th t acceleratederosion (caused by hurnan acLf vi ties) contributesabout 402 of the total sedimentgenerated in the watershed. Almost a11of the accelerated erosion is associatedwith agriculture,2.2 CLIMATEThe climate of the area is Medi terranean:rnoderate temperatures, arid summers,and relatively moist winters, Thereason for the region's rnoderate temperatureregime is the Pacific Ocean, a highlyconservative thermal mass over whichwesterly, onshore winds prevail exceptfrom November to January (de Violini1975),Monthly mean air temperatures of thewarrlrest and coldest months (Figure 5ajdiffer by only +3.5"G and -3.1°C from theannual mean of 14.7"C. The mean dailyrange in temperature is least in June,varying 7.3"C from a minirnum of l2.3"C toa maximuirl of 19.6"C, and greatest inNovember, varying 10.6OC from a minimumof 9,Z°C to a maximum of 19.B°C, only3.3"C inore than in June. Even the minimumtemperature recorded in 26 years is notparticularly extreme (-2.8"C or 9.4"Cbelow the average minimum of the coldestmonth; de Violini 1975). However, thehigh temperature discrepancies aregrea &err The record high was 40.0°C,17.9"C higher than the average maxiinurn ofthe warmest month. More importantly,frorn July 1976 through January 1981,temperatures were greater than 10°C abovethe average maximum of the wannest monthinore than 2 days per year, on theaverage, Curiously, these extremes werenot during the height of summer (Julyand August). Rather, they were bothbefore (May and June) and especiallyafter (Septanber, October, and evenNovember).During October and November, the hotspells are usually associated with verylow relative humidities and high winds,the so-called Santa Anas, when the prevailingwesterlies are supplanted for upto a few days at a time by northeasterlywinds swooping down the canyons from thehigh desert--the air is hot to beginwith and rises even more in tmperatureas the air mass descends and is compressed.The significance of the hot,dry winds at this time of year will beapparent following the discussion of precipitation.General ly, the daily and seasonal temperaturefluctuations tend to increasewith distance from the ocean, and temperaturedecreases with elevation. Locallythis pattern is strongly modified bytile winds, because of the orientation ofthe watershed. Thus, most of the timethe prevailing westerly winds transmitthe moderating inf 1 uence of the oceanthroughout the coastal plain and up intothe east-west trending va1 leys. Nevertheless,both higher maximum and lpwerminimum temperatures certainly occur inthe more landward parts of the watershedthan at Mugu Lagoon.The other important characteristic of aPlediterranean climate is that the relativelysmall annual precipitation isheavily concentrated in the cooler partof the year. Certainly this is the casefor Mugu Lagoon (Figure 5b). Ninety-sixpercent of the year1 y total precipitationfalls in the 6 months from November toApril. The contrasting records for theyears of lowest and highest precipitationare plotted along with the 34-year wanto give some idea of the extent of yearto-yearvariation (Figure 5b). Yearlytotals were more than twice the 34-yearaverage in 2 years, more than 1.5 timesthe average in 6 years, and less than

200 % OF344% MEANFigure 5. Characteristics of the climate of Mugu Lagoon: (a) air temperature,(b) ~ltonthly precipitation, and (c) the nurnber of years with differentamaunrs of precipitation, grouped in lil",;ncrment; of the 34-year mean (adaptedfran de Violini 1975 and unpublished records).

one-halfttne average in C years (Figure5c). Rainfa:? is concentraeed into shortperiods :di tilin the 6-iilontii nlu'lst period,In 2 years out 3f 34, the aveyage annualrajnfal1 was exceeded by peci pi talionfallinc: in s single inlonth in 3 yearsover one-ha1 f of the ann!ial average fel 1in a single month (and in each of 2months in 1976 and 1980 for- a total of 1:o;currcncus). After these figures, itwil 1 cane as no surprise that even asingle storm, or more precisely a stonnseries, can dump more than trje annualaverage [as, for example, in February1962 anil January 1969),Both oi these character; stics of the1 ocal rai nf al 1 regime ('occurrencelimited to tne cool half of the year andthen falling in a relati~ely FPW majorstonns) have ser.m'ous imp1 -ations in thewatershed of Mugu Lagc >r;. Potentialevapotranspiration is more than 70 cmduring the growing season; yet, becausewater is rapidly removed from the surfacelayers of the soil, the estimated actualevavotranspiration is 25 - 30 cm. Sincealmost no rain fails after April, rangegrasses are likely to dry out by earlyJune (Soil Conservation Service 1970),with the four hottest and four of thedriest months yet to come. When theSanta Anas blow near the end of thisperiod, the hot, dry, fast-moving airdesiccates even the most deeply rootedvegetatioo.Fires iyni ted under these condi tionstend to burn out of control until theSantd Ana conditions abate. In the meantime,thousands of acres of vegetationcan be consumed. Based on records fortheir study area in the western TransverseRanges, which included substantialparts of the watershed of Mugu Lagoon,Scott and Wi1 liams (1978) cited annualburn rates of 0.42% of the total area,although longer records from the nationalforests imnlediately to the north indicatethat a higher rate might be more appropriate.This suggests that an average of2 kn2 of the rugged part of the watershedis bared by fire each year, with theprevious! y described ten-fol d or moremagnification oF sediment yield. Even intile dbsenlce oP fire, the veyetdtion ofthe watershed is in very poor conditionby the next rainy season. Undoubtedlythis also contributes to the highsediixent yields characteristic of theregion.The siuni ficance of the concentrationof rainfall in major, protracted stormsis given in Scott and Williams"l9788)description of the January 1369 event:"Major stonns, like those of March 1938and January and February 1969, havefollowed a generally similar patternthat can be expected to recur in futuremajor stornls. The stom of January18-27, 1969, was typical: The circulationpattern of a low pressure centerin the Pacific permitted intensestreaming of northeaskard moving,moisture-laden air as a succession ofstorm fronts. Precipitation was lightunti 1 January 19 when intensity increasedsharply. Heavy precipitationoccurred throughout most of January 19-26, was interrupted by a brief respiteon January 22, and then climaxed onJanuary 25."The January 1369 storm generally producedpeak discharges equal to orgreater than those of the 1938 stonn inVentura County and western Los AngelesCounty. The 1938 storm had been thegreatest storm of recent times, atleast since the legendary flood of1862, and its peak discharges andsediment yields have been widely usedas standards of flood magnitude and ascriteria for impoundment structures.. . ."In both the 1969 storm periods, surfacesaturation occurred we1 1 beforethe most intense precipitation, Similarantecedent conditions existed duringthe 1938 stom and can logicallybe assumed to recur during any futuremajor stom."Once soil is saturated, no matter whatthe soil type or cover is, a71 subsequentprecipitation will run off, Consquently,the same intensity of rain will yieldmuch greater peak runoffs after saturationthan before. Although the reiationshipis anythinq but direct or precise,analyses made under local conditionssiiggzst that sediment yief d f; 2 F~";nctior:of peak runoff flow to the 1.67 power(Scott and Wil 'lfams 1978, citing Ferrel?

1959). If so, a doubling in peak flowwould be associated with inore than atripling in sediment yield. In extremecases, soil saturation on steep slopesmay result in slope failure and slumping,partly accounting for the extremesediment input to places like MbguLagoon.Steffen (1982) pointed out one additionalfeature of the tirning of precipitationin this region that is inherentlyinteresting and bears on this matter ofsediment yield. Bui 1 ding on Troxel l andHofmann's (1954) interpretation of variationsin tree-ring width as evidence of along succession of a1 ternating wet anddry periods from 1385 to the present inthe Los Angeles region (Figure 6),Steffen suggested the high li kel ihoodthat major storms at the beginning of awet sequence (median length 12 yearsduring 1385 - 1954) would cause much moreerosion. He based this conclusion on theobservation that the condition of thevegetation would be worst at the end of adry sequence (median length 15 years overthe same time span) but would improverapidly during a wet sequence, thereafterlessening the erosive impacts of storms,2.3 HYDROLOGYRunoff is rapid in the Mugu Lagoonwatershed because so much of the watershedis steep, yet low enough in elevationthat precipitation is not stored assnowpack. The rapid runoff, coupled withthe concentration of rainfall into a fewmajor stonns usual ly separated by dryspells of a few to several weeks, meansthat there is little or no surface flowin the lower reaches of local streamsexcept during and immediately afterstorms. Almost all freshwater inflow toMugu Lagoon, therefore, occurs fromNovember to April (Figures 5b and 7a);even within that winter period, mostfreshwater inflow is concentrated in afew pulses (Figure 7b). These gluts offreshwater during storms can carry vastamounts of suspended material that, inturn, can be deposited in the stillwaters of the lagoon. The concentrationof freshwater inputs in rare but extreme1 IPrec tprtat~nn at Los Angeles,IFigure 6. Wet and dry perjods in southern California (fromTroxell and Wufmann 1954),14

Figure 7. Streamflow in Calleguas Creek: (a) mean flow in different months 1969-77, 1978, and 1980; (b) mean flow by day in 1980 (from USGS records for the gaugeat Camaril lo State Hospital ).events is responsible for some strikingeffects which will be discussed after thebiota has been introduced. Here, itwill suffice to say that the freshwaterinput to Mugu Lagoon cornpl etely flushesthe lagoon for short periods of timerather than creating a longitudinal salinitygradient that moves up or down theestuary as the freshwater input changesseasonally. During the remainder of theyear, the lagoon is completely marine.The preceding general ization is notapplicable at the very mouth of Cal leguasCreek. Agricultural irrigation and sewageplant return waters make for a continuous,small input of freshwater.Because much of this water comes directlyfrom intensively cultivated lands, toxicsubstances and nutrients could affectwater quality. Little information onthis problem or this part of the lagoois available (see Section 7.3).Mugu Lagoon continues to be marinedominatedmost of the time, even since ithas become an estuary. The tides are responsiblefor the majority of day-to-dayinputs and removals of materials. Thetidal prism (volume of water moved in andout of the lagoon by the tides) is largecompared to the volume retained at lowestwater, Persistent southeast longshorecurrents prevail along the coast in thisregion. This assures that very little ofthe water departing the lagoon on the ebb

tide is returned on the Sol lowing floodtide; i,e., the saw water nass is notunder the inf'luence of lagoonal conditionsfor long.The tides thmselves differ frcxn onetide to the next (mixed semi-diurnal patterncharacteristic of this coast), frmweek to week (spring-neap a1 ternation),and from season to season (higher highsand lower lows in summer and winter thanin spring and autumn). The rnaxirnunl tidalrange is 3 m. A sill at approximatelymean sea level at the mouth of the lagooneliminates changes in water l eve1 belowmean sea level within the lagoon andreduces the maximum tidal range of thelagoon to 1.7 m above mean sea level(Figure 8). Consequerttly, on some neaptides the volume of water exchanged isnegligible, whereas on spring tides it ismore than three times the volume retainedat low water, at least in the eastern ann(Onuf and Quammen 19831, Not on1 y areupper intertidal areas submerged less ofthe time than lower intertidal areas, butalso the interval between their subn~ergencesbecomes increasing 1y variable.The lowest intertidal areas are submergedat least once a day, whereas at+1.5 v lZLLW (Mean Lower tow Water, thelong-term average e?evation of the sea arthe lower low tide each daysthe standardtidal datum of the region), periods ofconsecutive daily submergence lasting 4to 25 days are separated by 1- to iidayperiods wi thout submergence, At+2.0 rn MLLW, 2- to 7-day periods of consecutivedaily submergence are separatedby as few as 7 to as many as 56 dayswithout submergence. There js little orno la5 in the times of spring high tidesbetween ocean and lagoon; however, theremay be more than an hour's difference inthe timing of high tides during otherportions of the lunar cycle.Because of the relatively large tidalexchange of water within the lagoon mostof the time and the narrow opening to thesea, currents are fast near the mouth.Currents were measured at 3.7 km/h on aneap tide, and were estimated to be morethan 10 km/h on spring tides (Wanne1971). The sill at the mouth has theeffect of ~rolonging the ebb portion ofeFloodfng and drainage;rbove 1 5.11'1 (laturn \+1.5mMSL + 0.7mMLLW 0/ Fioodin(] ,and dra~rlancr ~n the irlooon,I -i 1July 6 / July 7 1 July 8 July 9MSL = mean sea levelMLLW = mean lower low waterFigure 8. Tidal curves for several days in June and July 1981. (A) Curves forspring tldes, showing times of flooding and drainage in the lagoon and times offJoocifrag and drainage above the 1-5-m datum, the approximate lower boundary of thesalt marsh. (B) Times of flooding and drainage dcring neap tides (from National&@an Survey tidal curves for Outer Los Angeles Harbor),

tddai cycles and shortenin2 the floodoortion, ,vhlc!~ h turn is respons!bie forhigher velocity currents or^ +load thanebb tides (i,e,, the same volume of water!nust enter in less time), These currentsare turbulent and ~rovide good mixing,:n the open expanses of water away fromthe mouth, tidal currents are slow andare probably jnsuffl'cient to cause muchmixing. However, these areas are snal-'ow. Yovements of water generated byeven light breezes apparently are sufficientto cause mixing. In hundreds ofdissol ved oxygen determinations of watercoliected near the bottom a'n conjunctronwith primary productivity studies,anaerobic conditions (signifying noinixi ng) were never encountered (ShafferP982),2.4 THE PHYSlCQCHEMlCAk ENVIRONMENTWater TemperatureThe physicochemical environment isstrongly under the influence of thenydrol ogical regime. The inoderate temperaturesof the ocean at the mouthgovern the temperatures wi thin the7 agoon. Surface water temperaturesmeasured at Zuma Beach, approximately25 km to the southeast, range from 13°Cto 18°C (monthly means), 12°C to 21°C(mean monthly maxima and minima), and g0Cto 22°C (absolute maximum and minimum)(Cal ifornia Water Resources Control Board1979). Secause of the rapid tidal flushingof the lagoon, factors operatingwithin the lagoon are of secondary importance.However, in the shallower andmore landward subtidal areas, air temperatureand insolation become increasinglyimportant. Of course, at thesurface in the intertidal zone thesefactors have to predominate when the tideis out. For the emergent vascular plantsof the salt marsh, this will be the greatmjority of the time.'tlo systematic measurements of watertemperature within the lagoon nave beenqade to evaluate the extent that airtemperature, insolation, and depth influencetemperature; however, two data setszuggest thst the modify in^ effect ofshal low depths can be substantial.di l son (1980) made hourly measurementsir; the middle of the sand channel ieadkgfrom the mouth of the lagoon intothe eastern arm and 45 m away in themiddle of a subtidai flat. At low tidethe former was covered by 50 cm of waterand the latter by 15 cm. For the 6 mea-surement days (a1 l during summer), midnatertemperatures at the deeper stationalways exceeded those at the shallowerstation at night (12 a.m. - 5 a.m.);during the day (10 a.m. - 3 D.m.1 theshall ow station was considerao7y warmerthan the deeper station. Such temperaturedifferences are striking and surprising,given the rapidly flowing watersof the sand channel.DuBois (1981) re1 ated temperaturesmeasured in the inner, broad, open waterpart of the eastern arm of the lagoon(termed subtidal pond by Harrne [1971])with ocean temperatures near the mouth ofthe lagoon. Even in the early summermornins when lasoon waters would havecooled- to their greatest extent, temperatureswere higher in the lagoon. In thewinter, when aay length is short andinsolation is reduced, water temperaturein the lagoon at night would be expectedto be lower than offshore.Sal i ni tyNo systematic measurements of salinityhave been made in Mugu Lagoon. Giventhe virtual absence of surface flows offreshwater except during storms, there isevery reason to expect dilution by freshwaterto be brief. The abundance oflong-1 ived stenohal ine marine organismssuggests that even brief dilutions substantiallybelow 34% are rare (Wame1971) ; however, dilution by freshwaterwas almost certainly involved in the dieoffsof the sand do1 lar Dendraster+-excentricusand the bubble shell 3ul la ouf dir- ana In 1969, 1978, and 19Clln ortunatelv.salinity has not been measured atthe (eights of khe storms when the reductionswere greatest, The only relevantmeasurements were 19 and 28 ppt, I and 2'days respectively, after a 2-crn rainfall,culminating a 16-day rainy spell in whicha total of 15cm of precipitation hadfa1 leg (pers, observ. 1, Apparently,there is a rapid return to marine con&-tions.

Although Mugu Lagoon has close tomarine salinities (34 ppt) most of thetime, the three major divisions of thelagoon must differ somewhat. The easternarm is the most nearly marine. it isvirtually without a watershed, beingflanked by a narrow sandspi t on one sideand a steep mountain on the other (a440-m peak within 1.5 km of the edge ofthe lagoon). Furthermore, the opening tothe ocean is closer than any long-lastingfreshwater source (Figure 2). The centralbasin receives the major inletstream, but this stream is channelizedall the way to its point of dischargeinto an artificially deepened area, witha direct path from there out the mouth ofthe lagoon, Only in the western extremityof the western arm is a longer-lastinggradational salinity regime likely. Thispart of the lagoon is partly under theinfluence of the coastal plain. Becauseof the low re1 ief, water runs off slowlyeven through the network of agriculturaldrainage di tches in the area (Figure 2).Also, the western part of the lagoon consistsmainly of emergent marsh and longshallow channels, for the most part notconfined by artificial levees. tlere,freshwater inputs might be triore persistent.Dissolved Oxygen-Dissolved oxygen generally is high inthe waters of the lagoon because of hightidal exchange rates and shallow depthseasily [nixed by winds, The only glaringexception is that reducing conditionsoften develop beneath senescent mats ofthe green algae Enterwnor ha and Ulva,both in the d e e p e d the lagoonand in a wrack line at the edge of themarsh in late summer. This affects theunderlying sediments btr'i anpa rent1 y doprlittle to the overlying water.- Bottom SedimentsWarme (1971) and Biddle (1976) describedthe sedii~lent characteristics ofthe eastern arm of Mugu Lagoon. There isno systematic appraisal of the rest ofthe lagoon, Within the edstern an twosediment gradients exist. Generally,sediments become firrzr grained frwu, westto east (increaslng distances front themouth) and south to north (frm tile sand-spit, across the subtidaf "ponds," andacross the salt marsh), The west-eastgradient is a function of the reducedvelocities of tidal iy generated watercurrents at greater distances fron~ themouth. The south-north gradient is theresult of a composite of factors.The south shore of the lagoon is enrichedin sand over what it would otherwjsebe by occasional overwash of materialfrom the ocean beach. This happenswhen exceptionally high surf coincideswith spring tides. Initially, the inputof new sand is restricted to a smalldelta projecting into the lagoon, Subsequently,that sand is distributed bythe longshore tidal currents along thewhole south side. Even in the deepestparts of the subtidal ponds, sand (particles>63 urn in diameter) predominateover mud (Wanne 1971). This suggeststhat water movements are strong enougheven here to keep fine particles in suspensionor remobilize them. The otherpossible explanation is that the sourceof fine particles is small compared tothe source of sand. Aeolian depositionof sand by wind may explain further theprevalence of sand in the middle of thesubtidal ponds.Silts and clays predoininate only in thesalt marsh or in bare areas and depressionswithin the salt marsh (Warme 1971).Here, tidal currents are weak, becauserelatively smaf 1 volumes of water arepassing over any given point in a tidalcycle. Furthermore, the vegetation bafflescurrents and reduces the turbulenceassociated with waves that otherwisemight cause the suspension and removal offine particles. (This analysis isfounded on the low input of fine sediments,in the aftermath of major stormcauseddeposition of fine sediments in1978, it is no longer applicable, as willbe described later.)Solar RadiationIn addition to its considerable influenceon the temperature regime of ashaf low aquatic ecosystem, solar radi a-tian is even more important as a majorSetcnninant of prfnary prodtrctivi ty,Average daily incident solar radiation inthe phofosynthetical 1 y artive region

(PA?., a~arox~matei: RaIF c" ehr totalinciaen: enercjy ir the vislble saeccruvgrange-: fie; 15 Er~steins Qf ' per P-' ~e\-< - 7-1.aa:tm2 P " L ~n Decembe- 12 52E P 2 - I** hay (Shaffer and 0nr:f 19L;:,:,F'agilr~ 9 , difference ir daj 7anntsfron 1'' xs 4,- h accounts foh- 27% :lf tbcIncrease, ani th6 higher i~te?slrv 3;sola- raslatso. caused bj the big?@-an9.e or IQCIQ~~CE dur-ing th; susnmcaccounx>top mas: of the re"U, C3ai#!covnr snc ~ t atte~dant seffe~t- s31aaradSat:or. snowec rmaskabiy i-itsvl2 wX9jatlor.over the year, eve? tha,iafis a!precipitat~o-r 7s s q-the wknter ;F?cj~:r~Y,, 1 ~ J s~z' Sr varjatiori is bectiusc fog;are ~rnrn0~ :I* tile summer, Fo' owqanfsmsiv tho_ water :c,~);w? and an E~F- ~~ttot t ,tcarbiai ty at-tenuat.es the I-FIJ~ c '~rthel-,rn prcrnort~or, i-3 ehe c~n:entr?~ctort o-SGsDended mattes ana depW effec'7 5 greates L nveVs unconso Yiadtel mudaybottoms ana leasr, ove~x~ancl [Shafrer at-$-1Onus 1982 I *Nutrient;No dat3 are avaigable on nutrient copcentrationi~ tne water column or irtsediments, Inferences a~out the nutrientregime are deferred ts Section 5.6, afterotber infonnat13r about the ecosystem hasbc@n presentee ,Figure 9. Meah daiSy solar radiatios; i~E~nste~ns (from Shaffer and Qnuf 19851 andsky cover (10-year average, January 1965tnrougb Decein~er 1959; from de Vio'lini1975) In different months,

CHAPTER 3. PHYSiOGRAPHYAt Mugu Lagoon, the steep gradients inphysical factors where land, sea andfreshwater meet create a wide spectrumof different living environments in asmall geographic area. The gradientsthat interact to create a mosaic of differenthabitat types were described inthe preceding chapter: current velocities,substrate texture, light, elevation,time of submergence, salinity(occasional ly) , and temperature. Becauseof large changes in some of the factorsafter a major storm in 1978, the physiographyof Mugu Lagoon is described inthis chapter in two parts: before 1978and after.3.1 STRUCTURAL COMPOMENTS-BEFORE 1978The major structural features of theMugu Lagoon ecosystem are the: (1) tidalinlet and delta, (2) subtidal channels,(3) subtidal ponds (Warnie 1971) or pemanentopen water, (4) tidal flats, (5)tidal marsh, (6) tidal creeks, (7) saltpans, (8) natural adjacent upland (barrierspit), (9) adjacent upland that isdisturbed open space, (10) developedadjacent upland, and (11) the nearshorePacific Ocean. Features 1-7 are exclusivelypart of the estuarine ecosystem,whereas Features 8-11 are only marginal lypart of the estuarine ecosystem. Adjacentuplands are divided into three categories(Features 8-10], because they havedistinctly different re1 ationships withthe aquatic part of the system. Theserelationships will be discussed only inthe most general terms, Feature 11 isimmense] y more iniportant than adjacentuplands as an influence on the lagoon, asis the influence of remote parts of thewatershed transmitted by Call eguas Creek.Tidal Inlet and DeltaThis physiographic camponent is characterizedby shal low depths (predominantlyintertidal) , the highest current ve1 ocitiesexperienced inside the lagoon, andconsequent1 y, an unstable bottom of sandand shell fragments. Although small inarea at any one time, the inlet and deltaexert an influence over a much largerarea in three ways. First, the inletmigrates along the spit. Second, theelevation of the inlet sediment bottomchanges, and with it the depth, duration,and periodicity of inundation of areasinside the lagoon. Third, the inlet is amajor source of sand for the lagoon.All of these effects arise from thesame set of processes, for the most partoperating outside the lagoon. The movementof sand along the coast is mostlyfrom northwest to southeast. Littoraldrift of sand along a beach occurs whenwaves approach at an angle rather thanperpendicular to the coast. Westerlywinds strongly prevail in this regionmost of the time, as do the waves thatthey generate. Furthermore, the southwardcurve of the coast farther east(Figure I) and the islands offshore blockor moderate the impact of waves arrivingfrom other directions. In consequence,sand originally supplied by the Venturaand Santa Clara Rivers is deliveredalmost continuous1 y (but in varyingamounts depending on wave conditions) tothe northwest bank of the tidal inlet.This bank builds out into the channel,and accordingly, the southeast bank musterode if the same channel size is to bemaintained. Hence, the inlet migrates tothe southeast,Of course, the same size inlet channelis not always maintained. For instance,

when periods of high sand supply bylittoral drift coincide with neap tides,the tidal inlet can fi'f 1 partly or cmpletely. Under those cundi tions, thesmall volumes of water moving through themouth provide insufficient force to clearthe added sand. Subsequent higher tidesfill the lagoon, but less water willdrain out than previously. Greatervoiuines will be retained at low tide;less mixing and exchange will occur,This condition will persist until extremehigh spring tides move enough water fastenough to re-excavate the inlet channel.Littoral drift and inlet migrationassure that there is a considerable movementof sand and water into and out ofthe tidal inlet. However, because thespeeds of tidal currents are higher during flood than ebb phasc T of the samecycle (see Chapter 2), mLre sand entersthe lagoon than departs. This provides asupply of new sand to the lagoon andaccounts for the flood-tide delta and theinstabil i ty of the sand bottom.Inlet migration at Mugu Lagoon is partof a repeating cycle of opening, migration,and closure. The fol lowing descriptiondraws heavily on John Warme'sdetailed analysis (1971). As the tidalinlet migrates toward the southeast endof the lagoon, the flood-tide supply ofwater for the entire lagoon must passthrough a long and meandering channel.This retards delivery so that relativelylittle water can enter the lagoon beforethe high tide has passed. The resultingflows are insufficient to keep the mouthopen, even on spring tides. Consequently,the mouth closes and remains closeduntil winter storms supply enough freshwaterto overflow the barrier spit at its1 owest point. Normal ly, the overflowwill be near the head of the Mugu SubmarineCanyon because its deep watercauses the refraction of waves. Thisreduces their energy when they break onshore nearby, so that the berm of thebeach is not built as high there. Thebreach erodes the spit and develops intoa new tidal inlet. Inlet migration proceedssoutheastward until the cycle iscmpleted by another closure,Apparently there were several cyclesduring the 1960is, when the Navy inter-vened to shorten the periods of closureby bulldozing a new channel shortly afterthe inlet closed (Warme 1971). Recently,the cycles have been somewhat different:a new tidal inlet formed opposite themouth of Caileguas Creek before or justas the old inlet closed, some hundreds ofmeters southeast along the barrier spit.The northwest limit for the location ofthe inlet is fixed by the placement ofriprap along part of the spit. The presenceof we1 1 -established dune vegetationbeginning approximately 1 km to thesoutheast indicates that this had beenthe down-current limit of inlet migrationfor a long time. Inspection of sevenaerial photographs from 1959 to 1979suggests that this was also the mostcommon location of the inlet.The most recently completed cycle ofinlet migration did not follow the abovementionedpattern. This time the inletmigrated its usual 800 - 1,000 m betweenFebruary and September 1980, remainedthere through June 1981, and then, insteadof reinitiating the cycle oppositethe mouth of Cal leguas Creek, continuedits movement to the southeast. By August1981, the tidal inlet had moved another150 m, and finally, in February 1982 theinlet closed after moving another 150 m.The inlet then reopened 1,300 m to thenorthwest. Before migration ceased, a300-111 strip of deeply rooted dune vegetationwas destroyed. Presumably, thisextreme cycle of inlet migration resultedfrom a major change in 1980 or 1981 inthe coastal processes that move materialson, off, and along the shore.Subtidal ChannelThe only channel in the eastern arm ofMugu Lagoon that always has substantialflow links the tidal inlet and tidaldelta with the subtidal ponds of the arm(Figure 10). The subtidal channel isquite uniform in width (approximately50 m) but varies in length from 700 to1,400 m according to the location of thetidal inlet and de1 ta, The subtidalchannel is 10-30 cm deep at low water forthe most part, but occasional depressionsapproach 1 m deep. The bottom is morethan 95% sand throughout (particlesgreater than 0.063 mm diameter). Maximalcurrent speeds have not been measured

:ie ?is$:';aa! cnanne?: ;hey are 3r.g-1 y "ess :nan those mat can affect:idal delta wt much yeater thands :$at 3ffect other 3arts ~f *hen :except tie adjacent anzertzda'irhtts), 2iarrents are neve* Powerenoughin any ~ldal cyc;e to $njfte ",an the top *ew layers of ";a5ns In the subtidal channel, whereasqore yxtensive a1 tevations areble in a snort time Sn z3e delta,reater stability of the srl@strate 117ubtidal channel is very im~rtanto-iota, ds will become apparent In thesbtldal Ponds and Other Areas- f Permanent Open WaterAreas of permanent open water make upaout one-fifth of the Mugu Eaqoon estuarineecosystem; however, only 4heiubtidal ponds of the eastern arm havesen described in detail {Warme 1971;'igure lo), The greatest depth recorded31 ong Warme \ to~ographic transects was;pproximately -0.3 ft MLLW, which would:orrespond to a water depth of approxilately1.2 m at low water in the lagoon,Tidal currents are barely perceptible,except where the subtidal channel emptieslnto the western pond and in the constrictedareas between marsh islands andthe adjacent mainland mrsh. Oftensurface currents generated by the windare more apparent than the tidal currents.Because of the slow movements ofthe water, much finer particles can anddo settle out than in the inlet, delta,and channel envi roments,The hydrodynamic environment allows forthe accumulation of fine particles in thesediments in the subtidal ponds; nonetheless,sand continues to dominate evenhere. Sand content ranged from 50% to90% by weight in "dame's (1971) samplesfrom the subtidal ponds. In addition,the finer particles were confined to thesurface layer (Figure 11). Finally, therewas a dearth of intermediate sizes (evidentin the abrupt change in slope of thecurnula tive percentage plots of grain-s izedistribution; Figure 11),These characteristics suggest severalthings, First, two different sources ofsediments and mdes of their introductio?1 I->, 5 2 3 4 5 0 7 8 9 1 0+- - Sand --I -- Silt -------I - Clay -Figurre 11. Variation in substrate texture~ith depth from a core taken in the middleof the eastern pond of the eastern arm,Nugu Lagoon (modified from Warme 1971).Snto the ponds are Implicated. Otherwise,fractions of ~ntermediate sizewould be more evident. The sand fractionhas its origin in the barrier spit andmay be delivered by the wind. Certainly4t is not carried suspended in the water.The predominantly clay fraction is terrigenousin origin, delivered to thecentral basin by Calleguas Creek and bytidal currents into the subtidal ponds ofthe eastern am. Although coarser materialundoubtedly is delivered to the centralbasin, the tidal currents are sufficientto transport only the fine fractioninto the ponds of the eastern arm.The second conclusion to be drawn fromthese observations ds that the supply offine particles 3s small, at least relativeto the supply of sand. Otherwise,fine particles should predominate, atleast in the surface layers. (The predominanceof sand at greater depths mightonly reflect a different depositionalenvironment in prlor times, such asancient beach or dunes In existence beforethe formation of the lagoon.) Theonly other possibility is that the depositionalenvironment is not what it seems;i.e., the "normal" situation of slow, weakwater movements is violated often enoughQ by great water t;u rbul ence generated by

high winds?) or is sufficiently modified(by activities of organisms?) to yield asediment in some ways more characteristicof a higher energy environment, ThisTatter a1 ternative 1 be consideredlater.Expanses of permanent open water in thecentral basin and the western arm of MuguLagoon differ from the subtidal ponds ofthe eastern arm in shape and other characteristics.The dredging of the centralbasin, the central basin's role asreceptacle for the discharges of the onlymajor inlet stream, and the separation ofmost of the central basin frm the barrierspit (the source of sand) all shouldmake for dl fferent environments thanthose just described for the eastern arm.The western arm has an almost uniformwidth frcnn end to end except where acauseway constricts water to a narrowculvert system, and no direct communicationwith the barrier spit. Thissuggests that the western arm will bemuch mddier than the eastern arm becausethe culverts restrict tidal exchange andbecause no supply of sand is availablefrom the barrier spit.Tidal FlatsIn the eastern arm, the tidal flatsadjacent to the subtidal channel aresubject to fast currents and are sandy,while those adjacent the subtidal pondsare subject to slow currents and havelarger fine fractions, In both cases,the sediments are coarser on the barriersplt side than on the mainland side. Inthese ways the different kinds of tidalflats have much more in common withadjacent subtidal areas than with eachother, In the western arm, tidal flatsare predominantly silts and clays.The botta of the inlet to Mugu Lagoonis at approximately mean sea level.Immediately outside the inlet the time oftidal exposure increases continuouslywith increasing elevation, starting atzelno at lowest low water (approximately-0.6 m MLLW), The distinction betweensubtidal and intertidal is blurred by thesurf. In contrast, everywhere inside thelagoon the time of subaerial exposurejumps dlrectly from zero to several hoursat the subtidal-intertidal boundary,because the water level jns'ide the lagoonremains at niean sea level the whole timethat the tjde is Delo~ mean sea level inthe adjacent ocean, The boundary is notblurred much by waves washing up theshore, Above this boundary the tine ofsubaeri a1 exposure increases continuouslywith increasing elevation. Thus, thereis no rarely exposed low intertidal zonein the lagoon. Being anywhere in theintertidal will mean at least severalhours of exposure for each tidal cycle.A1 though the differences between exposedand submerged conditions virtually di s-appear only a few millimeters into thesubstrate, they constitute rigorousphysiological chal lenges to the biotaconfined to the surface.Tidal MarshThe dominant feature of the tidal marshis its vascular plants. The plants areterrestrial in origin; hence, it is notsurprising that the marsh is confined tothe upper part of the intertidal, wheretime exposed to the air exceeds timecovered by water. Macdonald (1977) definedthe lower limit of the tidal marshas the elevation where time of maximumcontinuous submergence rises sharply froma level of about 7 h (Figure 12). Currentsare slow in the marsh and are lessat high elevations than low. Also, thevegetation retards flow and virtuallyeliminates wave action at the sedimentsurface. Consequently, some of thefinest sediments in the lagoon are foundhere. Nothing is known about the conditionsin the marsh surrounding thewestern arm; however, the gradient towardfiner sediments at higher elevations maybe reversed on the south side. Since themarsh is adjacent to the barrier beach,overwash and wind will supply largequantities of sand to the higher elevationshere, except where development hasel iminated the zone of contact (Figure10).Tidal CreeksTidal creeks de1 iver water to and frainterior parts of the marsh, There arefew at Mugu Lagoon, presumably becausethe marsh is narrow, being either confinedby a mountainside as in the easternarm or by artificial fill as in the

MHHW = mean hiahet high waterMLMVd -; mean iower high waterM~LW = meair Eovverlow waterSa! t PansThese features are in the highest partof the intertidal zone in the one area oflow slope that has not been altered byhuman activities (Figure 10, northeastfrom the central basin). Pans are locatedat an elevation approximately 2 mabove MLLW and are very rarely inundatedby tides. The highest are only reachedby storm tides. Uater stands in the pansfor long periods. Therefore, there isconsiderable evaporation, leaving thesalt behind and at the surface. Even ifprecipitation were more important thanthe tides in supplying water, the saltswould still be left at the surface, thusaccounting for the name "salt pan" andthe absence of persistent vegetation.Elevation above MLLWFigure 12. Duration of maximum tidalexposure (E) and submersion (Sl=Nov.1964; Sz=Jan. 1965) for Mission Bay Marsh(adapted from Macdonal d 1977).western arm. Creeks are best developedin the marsh surrounding the western arm(see frontispiece). The bottoms of thetidal creeks can be as much as 1 m deeperthan the adjacent marsh in their lowerreaches and are subtidal (Warme 1971).Smaller creeks and the heads of thelarger creeks differ less in elevationfrom the marsh and are intertidal. Currentsin the creeks, especially currentsin downstream portions, are faster thanin the adjacent marsh. Consequently, thesediments should be coarser. Samplesfrom a creek and from the marsh 75 maway were 33% and 6% sand, respectively(Warme 1966). Most of the tidal creeksare short (~0.5 km) because the saltmarsh is narrow. The only long tidalchannel extends a~proximately 4 km westfrom the western arm of the lagoon (Figure10).S i l t predominates in the salt pans andareas of high marsh immediately adjacent,unlike all other locations sampled in theeastern arm, suggesting the nearby SantaMonica Mountains as the localized sourceof the different sediments (Figure 13).In contrast, the tidal influence is sduncmmon and, when it does occur, soslight, that tidal waters could not carrymuch suspended material (even clays) intothe pans. Other samples relatively richin silts, collected from the heads oftidal creeks near the Santa MonicaMountains (Warme 1971), are consistentwith this interpretation.Summary of Wet1 and ComponentsThe tidal marsh has the greatest arealextent of a1 1 components of the MuguLagoon estuarine ecosystem, fol 1 owed bypermanent open water (accounting for lessthan one-third as much) and tidal flats(accounting for less than one-half thatof open water; Table 2). The western armis relatively rich in tidal flats, marsh,and creeks, whereas the central basin isdecidedly poor. In contrast, the centralbasin has much more permanent open water,and the eastern am has almost all thesalt pans.These differences in proportions arehardly surprising in view of the topographicfeatures of the different partsof the lagoon coupled with their ctll turalhistory. Thus, notwi thstands'ng majorlosses of tidal marsh to the development

SANDFigurn 13. (a) Sediment triangle and (b: mp snowing simples in which silts wererelatively enriched In surface sediment samples in the eastern am of Mugu Lagoon(adapted from Wame 1965. 1971).

-"Tabde 2. The strilcturdl ca7pa~ents 01 tbap P~l?agii Lagoon estuarine ecosystm: theirar.p,rl fir16 Jistp? biit-ioi: wi th-in the ecosys ta7 j subtidal and intertidal cmpormencs 1~n,! tLte irnjtit of ~ d GK q ;?tljaccnt ~ upland, (8dsed priialarily on Figure 10,)-_- _. ll_l_.p--l-. -"! of the total for the wholelagoon Iyinq within:4r2a I : of Eastern Central WesternCanaonen t (ha) k t ) total arm basin a rin----we-*Ti : sub tidal and intertidd; 597 100 2 2 16 6 2: ILi,+l inlet and d ~ td l'1 1 100Su'atiJfll cblanncl 1 100Sub3 dsl ponds or prirwr-i~n+apcn wdta- 111 19 19 54 32Tidal flats 51 Y 17 15 68T ti a 1 iF:d YS 11 38 T 64 18 5 77Tidal creeks 11 2 18 52Sal "uns 3 2 5 97 3Upland: call 22.2 100 2 4 P 1 6 5Natirral (barrier spit) 5,9 2 7 34 8 58ilis turbed operz space 7,11 35 10 21 63Devcl oped 5.9 27 Oa 298?io irtteraction with wctl~ndr 2,G I? 100 i) 0dMort of the upland edge on the Idntfwar;! side of the eastern a:?n is excludedbecause it was always so steep a\ t3 haw little role in the estuarine ecasystetn.of the Ndvai Air Statjon, the Iloodplai~isetting of the western ant1 still feadsco CI prevdlence of intertidal ccmnpon~ritsccanpiircd to the undeveloped eastern anti,v h is pressed against a mcrntainiank, Prcsurnably, sa 1 t pans were $:rev--aierlt atthe upper fringe of tnc mrsh-q thc western ann, but Mere filled vrhentw base was constructed. In the centralnasTn, dredging eliminated the lowerparts 9F the intertidal, while fil 1 clirnrnatedtne upper parts. The conseqdcnccwas the overwhelming predominance ofoennanent open water there,The three categories of adjacent ualannshave distinctly different relationswith the aauatic components of ths cccrsyst;an.Adjacent itpaand irr a nearlyrlat~~nra? condition is limited to the bar-rier spit and beach, It is a majorsource of sand for the lagoon. Thecoastal rtranrl and dune canmunities onthc spit are important because of theirrarity in the region; in addition, theyprovide habitat fov a relatively smalldariety of oorganisms that also use thelaqsan. nist.larbed open space, modifiedRy past lliirnao activity such as filling ordi kinrg, may be mowed or disked accasion-?liy, bmt far the mst pa?t is leftlone, 4s ~ith the barrier spit, it providesdl ternative habitat for a ma1 1v3riety of organisms that use the lagoon,The nrqanisms that use these two kinds ofup1 and-wetland transitions probably aredl" ffereqt, The deveS aped upland, of? theother hand, can be a source of inpots(pol iutc;r!ts, noise, and rapid novemenl ofplanes, vehicles, and oeople) that myreduce the ut il i tyof adjacent wet? andf2r the> biota normally associated withupland-wetland f-i~ges,

The amount of edge between each kind ofupland and its adjacent wetland wouldseem to be of greater significance thanthe area of upland in determining uplandcontribution to the estuarine ecosystem,Obviously, the width of the borderingupland also matters, but the use of adjacentupland by estuarine organisms probablyis a rapidly decreasing function ofdistance from the edge. Until we knowmuch more about what goes on landward ofthe upland-wetland edge, the length ofthe edge will have to serve as the bestfirst approximation of the contributionof each kind of upland.The three major lobes of the lagoondiffer radically in amounts of the threekinds of edge. Virtually a11 of thedeveloped edge is in the western arm, andthe eastern arm is proportionately richin natural edge. Despite the concentrationof development in the western arm,natural and disturbed open space accountfor 60% of the upland-wetland edge, Therole of roads is variable. The PacificCoast Highway, skirting the northern sideof the eastern arm (Figure 10), isfringed by a jumble of rocks and ana1 ms t-continuous wall of vegetali on thatdiffer little frm~ the original border ofrock rubble and vegetation at the foot sfthe Santa Monica Mountains, The heavilyused causeway crossing the western amshould perhaps be regarded as the extremeexarnpl e of a developed edge.3.2 STRUCTURAL COMPONENTS-AFTER 1978Sediment deposition caused a drastictransformation in the central basin ofMugu Lagoon sometime between 10 March1977 and 16 May 1978. This transf~rmationis illustrated in the series ofaeri a1 photographs appearing as Figure14. On the former date the central basinwas almost exclusively permanent openwater. Tidal flats were limited to asmall delta at the mouth of CalleguasCreek and the delta associated with thetidal inlet. Together they were lessthan one-third of the area of permanent1977Figure 14.The extent of intertidal flats in the

open water, By 16 May 1978, the proportio~swere almost reversed, There wastwice as aluch area af tidal flats as ofopen water, Between those two dates wasthe wettest season in the 36 years of thePoirt Mugu meteorological station, includingone protracted series of stormsthat diriy~ed 20.7 cm of preejplt8tion fn 9d2js (5-13 February 19781, Effects ofthe stonr? series were not limited to thecentrjl basin. Sediment samples anddeptil 11i7asurements of the lagoon ( t h ~easterr, arm in particular) frm theIQtiO's (Wam~e 19661, frm? the !978 stunnperiod (Jill Cermak, Univer5ity of California,Sdnta Barbara; unpubl, ,c?.), andfrm recent ~ork (Onuf and Qtiar~:~en 1983;Shaffer and Ondf 1983) have a1 locviid us toreconstruct a fairly cmp:e.le descriptionof the effects of the storri,The nlos t obvious cons^ ,uence of theston11 was that the bottorri imm=Jiatelychanqed over most of the eastern arm frombeing predominantly sandy to being muchfiner grained (Figure 15). Although someof the fine material at the surface wassel ective? y removed shortly thereafter,only the sandy-bottomed subtidal channelhad reverted to its former condition bythree li~onths after the storm (Figures 15and 16), Samples collected over a longerperiod on tidal flats bordering the subtidalchannel (Sites 5 and 6, Figure 16)and on inner lagoon subtidal and intertidalareas (Sites 8 through 11, figure16) indicate that the much finer surfacesediments deposited during the stormstill persist in the inner lagoon pondarea but no longer in the channel area(Figure 17).In addition to the sediment changesthat have lasted at least 2 years in thesubtidal pond, the sedimentation a1 so resultedin a substantial decrease in thedepth of the lagoon. If it is assumedthat all the change in elevation betweenWanne's (1971) original topographicaltransects in the mid-1960's and the resurveyingof the same general areas in1979 resulted from the February 1978storm, then Figure 18a shows the extentand distribution of filling caused by1978central basin of Mu9u Lagoon in different years,29

coarse to rnt~rmediaternterrrteniate to flnel~tEle rnsnj,ecoarse to faneFigure 16. Sediment-sampl in9 sites andareas of the lagoan with similar sedl":m?i'ttchanges in response to the mjo~ stom ofFebruary 11478, See F-igure 15 for examp1es of the sediment-size distributionsof the different areas over time,Figure 45, Sediment texture before,during, and after the major series ofstows in 1978; sites grouped accordinto similar histories of change. (a?coarse to fine; (b) coarse to internedlateto coarse; (c) intermediate to fine;(d) little change. Sample sites areshorn in Figure 16.Figure 17. Changes in surface-sediment texture at sites in tbe tidal channeland western pond (near sites 5 and 6, and sites '9, 10, and 11 of Figure 16,respective1 yf of the eastern an, &gu Lagoon,

Figure 78. Changes in depth of the eastern arm of Mugu Lagoon, caused primarily by thestorms af (a) February 1978 and (b) 1980.that storm, According to this analysis,the average depth of the lagoon (at lowwater) has decreased approximately 13 crn(252), and the deepest areas were fill edthe mst,Any cmpari sons between surveys ,mde soman3 years apart contain uncertainties,Confidence in the interpretation that theone stom accounted for mst of thecharge tier ires irmi the close agreementbetween the bathymtric changes inferredfrm surveys made many years apart andthe few direct naeasurments of the newtrwd layes made in the same locations, Inthese cases, we know from sampf es co9-7ected as few as 17 days before the stormand collected again at the same sites asfew as 3 aad 43 days after the stom,that approximately 10 cm of loose1 y cansolidatedpure mud (over 90% by weight4l.063 m in diametter) had been depositedon top of a compacted mddy sand (

Figure 19. The relationship of the eastern arm of Mugu Lagoon to inputs fromCal leguas Creek under different tidal conditions.appear that this is a necessary but notsufficient condition for storm-causedsedimentation in the eastern ann.(2) The earlier storms occurred duringtimes when the erosion potential of thewatershed was low. Erosion, and consequentlythe sediment load of streams,will be highest when the watershed isalready near saturation before the rnajorstorm and when the vegetation of thewatershed is in poor condition after asuccession of dry seasons. Both the 1978and 1980 storms were preceded by unusuallywet months, while both the 1962 and1969 storms were preceded by months ofnormal or subnormal precipitation. Thecondition of the vegetation in responseto prolonged drought is harder to assess.Steffen (1982) proposed the ciimulativedeviation from the long-term average precipitationas a meaningful measure ofvegetation condition. Here the criticalfeature is the length of time into along-term period of drl'er or wetter thannormal condi tions (downward and upwardtrends, respectively, in the plots ofcumulative deviation from the long-tenaverage precipitation). The first 31.years of rainfall records for Point Mugushow a major drying trend (Figure 20) inwhich wetter than nonnal years are fewand not in succession. Judging from therecords of the nearby Oxnard weather station,the beginning of the Point Mugurecord was the beginning of this dry period;thus, the major storms of February1962 and January 1969 were one-half andthree-quarters of the way through the dryperiod, ldhile they were major storms,they certainly did not end the dry spell,That was left for a succession of wetterthan normal years beginning 9 yearslater, of which the February 1978 and1980 storms were a major and early part.These results suggest that droughtcauseddeterioration of the vegetationin the watershed could have contributedto the greater sedi:nentatjo.r resiiltin~from the later storms, This conclusionrequires that vegetation is appreciably

1950 1960 1970 1980Water year beginning July of.Figure 20. The cumulative deviationsfrm the long-tern mean precipitation(34-year record) at Point Mugu, California(based on de Violini 4975 and unpublishedrecords), See Figure 6 for longertime series in the region, A downwardtrend of points indicates precipitationbe1 cpcs the long-term average ( 1945-63,1968-76); a horizontal series indicatesprecipitation equal to the long-ternaverage (1963-1967); and an upward trendindicates precipi tahion above the longtermaverage ($976-1979).?es% caoable af retardi~tz er~s~o~at~ei adry per;od has been in proares5- -fa. 32years (as in K978), ctarro8re.t cf~ .!J yen?-(35 in 19691, and that ;nore tharl :1 warsof above-nomal preci oi tacf3r: r~ts",e.is~nbefore the vegetation improves eco.JgY toretsrd erosion effectively, 2th~rwi 52,major sedimenta"lon should nrz: haw gl:-curred in 1980, Bath r u m q c'wplausible but lack irldepeod.ant vura f ica-i *cl Or1 *.(3) De?ve~opment of the waters her1 sincc19G9 resulted in more eriashan that! dupinqthe 4960k.,, Baring soil or} steep r,:o~r?swill certainly accelerate erosion; tnisis happening in the watershed of MugifLagoon on a massive scale (Figure 21) forreasons Stated in Chapter I, This activityhas became much rnore widespread since2969 than before and could account f ~ rthe difference in effects between theearlier and later storms,mrri 21. Aerial ptyotoyr~rpph of hiTlsidc devel~pmenl mar Moorpark, Catifcrnia, 1979,34

Chariges T"n land case before znd after196g have been deterinined from maps andphotqrdphs for the part of the Ca4 leguasCreek watershed lying within the Moorpark,Cal ifornia, U.S. Geol o~ical Surveytopographic quadrangle (Figure 22). Accordingto this analysis, of 211 hi1 lsideareas developed by 1979, 25% had beendeveloped by 1947; another 15% was devef -oped in the 22 years to 1969; and theremaining 60% was developed in only 10years frorn 1969 to 19713, This correspondsclosely to the 'largest area of'%hi yh rates of accelerated erosion"(caused by human activi ties) identifiedby Steffen (1982) and probably is representativeof all areas so designated(Figure 23). He estimated that acceleratederosion might account for 40% ofsediment generated in the Calleguas Creekwatershed and even more in the remaining18% of the whole Mugu Lagoon watershed;therefore, these changes in land useundoubtedly were responsible for largeincreases in the amount of sediments thatwere transported to Mugu Lagoon by majorstonns in 1978 and 1980, compared to 1969and earlier.Flat valley bottoFlat valley bottomFigure 22. The extent of hi1 lsjde development in one part of the watershed of MuguLagoon at different times (see dashed area in Figure 23).35

High rates of accelerated erosion (accelerated by humanactivity)Figure 23. Areas with high rates of accelerated and geologic erosion (frm Steffen1982). Dashed lines indicate the area represented in Figure 22.Accmpanyi ng the impacts of sedimentationhas been a catastrophic reduction incertain groups of the lagoon benthos dueto the reduction of salinities. Withincreased development and stonn runoff,these catastrophic reductions may becaused by smaller storms than in thepast.(4) The central basin had a greatercapacity to receive storm sediments duringthe 1960's. Until 1977 the centralbasin was a large expanse of open water(Figure 14) having been dredged approximately10 m deep in the early 1960's.The storm flows leaving the narrow confinesof the levees on Ca1 leguas Creekwould have spread out and slowed at thispoint, perhaps enough so that sedimentscould have settled within the centralbasin rather than within the eastern arm.A ma1 1 delta was present at the mouth ofCalleguas Creek at this time, and locrsc!mud was observed in the central basin butnot in the eastern arm after the 1962stom (MacGinj tie and MacGini tie 1969).The central basin ceased to be a body ofopen water during the 1978 storm (Figure14), after which it ceased to be a sinkfor suspended particulates before theycould reach the eastern arm.This then can explain the differentimpacts of the 1962 and 1969 stormsversus those in 1978 and 1980: until thecentral basin ceased to serve as a sedimenttrap, no storm could cause majordeposition of fine sediments in the easternarm. This explanation also resolvesthe dilemma of why a stonn-dumped layerof mud could persist where the bottomcreated by "natural " processes (movementsof water and air) had been predominantlysandy. The subtidal ponds always were aplace where fine material could settleand stay. The reason that fine materialconstituted so little of the bottm wasthat the source of supply was small relativeto the srapply of sand from the barrierspit. With the filling of the centralbasin, the supply of fine materialcarried as far as the eastern arm by

stor~ floi,is has ";creaSc?S and tne zrinousltof fine inaterial deposited on the bottmof the eastern ann has increased as w ~ l i ,The f;l!jng of the central bzsin is theproxin;ate explanation for ti]? aSrupi andlarge chanc;e irr the sedii:le:?t ~"ynairiics ofr4ugi; i.sg00n in 1978, Howi.ver, the otherthree factors cannot be ig9ot-ed: (I) thei;!?asing of stoms with the Yides will&ten-:ine to what extent sedii~ients aretransported into the eastern and wes.ternanns from now on; (2) the condition ofthe watershed in response to the c1 imaticcycle ~i17 determine hw much soil iseroded; and (3) continued development ofsteep hillsides has been and will continueto be a major determinant of thesediment supply, The supply of sedimentswi li probab:y increase as Inore hi? lsidesarc! developed; this will be compensatedfr: part by the vegetative cover duringthe wetter-than-normal period, but thiscondition wil'l be temporary. Filling ofthe lagoon will continue, especially ifstoms coincide with spring high tides.

CHAPTER 4. THE BBOTA:DISVRBBUBION ARID ABUNDANCEChristopher P. OnufandMi1 licent L. QuammenThe biota of Mugu Lagoon is rich inspecies. Forty-six vascular plantspecies, over 190 species of benthic invertebrates,39 fish species, 198 birdspecies, 11 species of reptiles and amphibians,and 41 mammal species have beenrecorded in the lagoon and surroundingwetlands (this report; Macdonald 1976b;Natural Resources Management Office, U. S.Naval Air Station, Point Mugu, unpubl.list). This a1 lows for a multitude ofassociations and interactions betweenspecies as we1 1 as with the physical environment.In this chapter we provide adescription of the spatial and temporaldistribution and abundances of the organisms,including the effects of the stormalteredphysiography. We leave to Chapter5 the discussion of what those organismsdo (especially to each other) and howtheir functioning provides much of theorganization that justifies the conceptsof "biotic community" and "ecosystem."4.1 THE PLANTSThe plants of Mugu Lagoon range fromsingle cells drifting in the water tosrnall shrubs rooted 1 rn deep or more intothe ground. Some are strictly limitedspltially, while others appear to have no1 i ~ni ts \.~i thin the tidally influenced area.Same achieve such dense cover that theyprovide most of the physical structure ofthe envl ronment for other organisms.Others, such as the microbial plants ofthe so-called "barren zone" of the tidalflats (Wame 1971), don" even appear tooccupy a site; yet these plants may bealmost as productive of new organic matteras the visual dominants and perhaps aremuch more productive of organic materialavailable for assimilation by consumers(Peterson and Peterson 1979). Final ly,all vary considerably in abundance or biomassseasonally and over longer periods.In some cases, the overwhelming dominantof one time may be hard to find the nextand may be unimportant 1 year later.Table 3 represents one attempt to depictthis variety in a way that displays theobvious patterns. In the body of thetable the symbols are an indication of therelative importance of each plant group ina habitat incorporating trophic (productivity,availability to consumers, nutritivevalue) and structural (influences onthe physical environment, provision ofhabitat for other organisms) considerations.The criteria are most objectivefor comparisons of the same plant speciesin different habitats and correspondclosely to biomass. Comparisons betweendifferent plant species, especial 1y betweendifferent general categories ofplants, are necessarily more subjective.Phytoplankton, Benthic Micro- and Macroalgae,and Submerged Vascular PlantsDespite the large extent of continuallysubmerged habitats within the lagoon, thecontribution of phytoplankton in numbersand bioinass is tiny. This is true evenwithin the water column, the one placephytoplankton might be expected to dominate.This conclusion is based on threelines of evidence: (1) Benthic diatoms

Table 3. The relative iniportance (see text) of different categories of plants in thedifferent: hab

UWQI Q).rm L Cr w+J& xr -5a,+-' LIlc -0s a,"LaLaz0yC'eraE m.r '+-

ch!orophy'll 2 per gram dr.y wcfght of sediment)at the beginning of the study inJune and July 1977, intemedlate and closeto constant (10-15 vgi'g) August throughDecember, very 'low (17 ug/g) in Januaryand February 1978, intermediate again inMarch, and high April - June. This periodwas almost evenly split by the Februarystorm that so radically transformed thebottom of the lagoon, so it is not knownwhether the spring increase is representativeof a "nonna'l" year, The winter 1 owis, however, since it was evident inJanuary.The short sampling period hampers theidentification of stom-related effects onthe benthic microflora. For June, theonly month sampled before and after theFebruary 1978 storm, chlorophyll a was 60%less in 1978 than 1977, suggesting a substantialdecline in biomass caused by thestorm. However, data for productivity inJuly, to be discussed in the next chapter,lead to the opposite conclusion. Apparently,the drastic transformation of thebottom of the lagoon from mostly sand tomostly mud did not cause a major change inmicrof'loral biomass. In contrast, anabrupt and persistent change in the spectralcharacteristics of pigment extracts,interpreted as a change in the ratio ofchlorophyll a to chlorophylls b and c,between JanuFry and February 1g8 in6-cates a major change in the species compositionof the microfloral canmuni ty(Figure 24). The observed pattern of agreat increase in chlorophyll a relativeto chlorophylls b and c is consrstent witha larger propo~tiona~e contribution ofChrysophytes, the blue-green component ofthe microflora (containing chlorophyll aonly) compared to diatoms (containin:chlorophy11s a and c) and green a1 gae(containing c~loroph~ls a, - b, and c)(Parsons and Takahashi 1973). In tur?;,this fits well the observations of manyothers that blue-green algae are mostabundant in association with fine sediments(e.g., Rheinheimer 1976).Prior to 1978 the subtidal parts of theeastern arm were about evenly split betweendense meadows of eelgrass and apparentiybare bottom covered by a microf7araIfilm very heavily dominated by diatoms.For relatively brief periods in the latespring and autumn, mats of the rnacroscopi:green alga Entermarpha would grow luxuriantlyalong much of the shoreline of thesubtida? ponds, both on the t-idal flatsand in the subtidal areas immediatelyadjace~t. Even when drained of water,these mats were several centimeters thick,The reason for ranking the macrophyteseven higher than the benthic diatoms inTable 3 is that the macrophytes comprisethe entire habitat in the specific situationsnoted. By virtue of their huge massand ability to occupy the whole volume ofthe aquatic habitat, not just its solidsurface, their impact probably is considerablygreater than that of the microfloralfilm. Trophically, this may not bethe case, although it is difficult to canparethe direct grazing pathways originatingin the microflora with the indirectgrazingdetrital pathways that are so muchmore important where macrophytes predominate.After the storm of 1978, cover by macroalgaeincreased greatly in subtidal areasand remained abundant for much 'longer per-iods in intertidal and subtidal zones. Inthe first year after the storm, Enteromorphaaccounted for the great majority ofcoverage. Since then, has becomeincreasingly abundant and now predominatesoverwhelmingly. It is impossible to discountthe effects of the major depositionsof mud in 1978 and 1980 in bringing aboutthese changes, a1 though the mechanism involved remains unknown.Through 1977, eel grass (Zostera marina)occurred in dense beds coverina aiGi%Zd,,mately half of the subtidal area in theeastern arm of the lagoon and extendinginto the lowermost part of the intertidalzone. Although no determinations ofbiomass and productivity have been made,both must have been large, as attested bythe predominance of dead eelgrass in thewrack at the high-tide line and strandedin the marsh (pers. observ.). Eelgrasswas a rwre important determinant ofhabitat characteristics than the macroa1gae, because it was abundant thrslighoiitthe year and widespread in the lagoon,Changes in eelgrass resulting fran theFebruary 1978 stom are relatively easy tointerpret, The :ength of eelcjrass variesaccording to the depth of the water ir;which the plants grow, On intertidalflats and in the shallowest subtidal

dreas, blades general 1 y are less than0.5 m long, whereas in the deepest part ofthe lagoon, their length usually exceedsI m long. The shallow-water plants werecompletely buried and apparently suffocated.In deeper areas most plantssurvived the initial inundation, becausetheir greater length insured that most ofeach plant was well above the bottm dl1of the time. However, the deep bedsthinned gradually over the next severalmonths until they too were extinct by fall1978. Probably this was the consequenceof the normal aging and sloughing off ofthe blades already in existence when thesediments were deposited, except in thiscase there was abnormal absence of replacement.New shoots develop frm the thickenedbasal portion of the plant, ordinarilylocated at the surface of the sediments.In ten sets of tagged plants that survivedthe initial burial, shoots continued todevelop, only now 10 - 15 an below thesurface (determined by removing the overburdenof new sediment fran the plants).However, none of the shoots reached thesurface, or if they reached the surface,they did not survive the 2 weeks untilthe next observation (Onuf, unpubl .sbserv.) . Apparent1 y, new shoots cannotpenetrate an overburden of I0 an of anaerabfc sediments.The eel grass beds have not recoveredsince. Only a few patches were seen in anaerial survey conducted as recently asSeptember 1986 (R. Dow, U.S. Naval AirStation, Point Mugu, Ca1 ifornia; pers.corn*),The Lower Marsh VegetationIn cgeneral , Jov Zedler's r~ionoaranh The~cology sf ~oufhern Gal i forni a doaswSalt Marshes: A Community Prof lle, a canpanionvolume. resents a mch fulleraccount of the emergent marsh than it ispossible to assemble from research conductedat Mugu Lagoon. Please consul tthis valuable source for topics such aszonatf on and plant-soil relationships,including responses to soil salinity andmof sture, Here we confine ourselves toaspects of the distribution of marshplantbiomass In the eastern arm of MuguLagoon that have been studied in detail-(Onuf uripubl,). These data nay be noteworthybecause they are unssual corfiyaredto data Fran other locations.The riiost obvious feature of the lowermarsh is the virtual rnot~ocufture of nprr-ennial pickleweed Sal jcornia virginica(Table 3). This trait is cmmon to a71coastal salt narshes from Long Beach tothe Golden Gate, apparently wi th d shgleexception el sewhere in Mugu Lagoon(Macdonal d and Barbour 1974). Cordgrass(Spartina foliosa) was virtually eliminatedby dredging in the 1950's and 1960's(Macdonald and Rarbour 1974). It ispresent today in four areas of the lagoonand is expanding in the western arm (R.Dow, pers. comm.). Zedler (1982) notedthe association of Spartina with "wetlandswith a history of good tidal flushing";however, this alone is not an adequateexplanation for its near absence from theeastern ann,The biomass of perennial pickleweed isdifferentiated into succulent green shootsand brown woody supporting stems (Figure25), the brown stems being the largerfraction throughout the year (Figure 26).Even though the succulent green shootscontinuously increased in biomass persquare meter between January and June andmaintained near maximum bi mass throughAugust, there were no detectable changes(by analysis of variance) in total biomass(green + 1 ive brown parts) over the courseof a year, While this partly reflects thegreat spatial heterogeneity af the marsh(see next paragraph), it is more an indicationof the protracted growing season ofsouthern California and the large allocationof biomass in perennial pickleweed towoody supporting stems. Apparently, theperiods of accumulation and death of woodyparts overlap so much that net changescannot be detected during the year,despite the strong seasonality in thebiomass of the succulent green growingtips.Onuf analyzed aspects of the spatialheterogeneity in marsh plant biomass inthe marshes fringing the eastern arm ofthe lagoon. Three features were identified:(1) Marsh plant biomass ms asvariable on a small scale (decimeters) ason a larger scale (meters), (2) Bianasstended ta decrease with distance frm the

lower ?dge of the inilrsh (Figure 27), and(3) Biomass patterns as a Function of distancefro3 the nrouth of the iagoon changedfrm year 'to year from 1978 to 1981,Figure 26. The biomass of Salicorniavirginica in the lower marsh at MuguLagoon in different months.Biomass tended to be high near the mouthof the lagoon and much lower far from themouth in 1978. The strength of this trendprogressively weakened in 1979 and 1980and reversed in 1981, when biomass waslowest near the mouth (Figure 28a). Thisshift in distributional pattern over timewas expressed as a highly significant yearx location interaction in analysis of variance,most easily visualized by plottingthe location means for each year as linearregressions of biomass vs. distance fromthe mouth of the lagoon (Figure 286).These last results provide informationabout the effects of major storms on thesalt marsh. Onuf et al. (1981a) interpretedthe higher biomass of all locationsFigure 25. The dominant plant of the salt Meters landward from lower edge of marshmarsh, perenni a1 pick1 eweed (Sal icorni avirginica), has succulent green shoots Figure 27. The biomass of Salicorniayear-round, but the woody brown supporting virgin-ica vs, distance frorii the lower edgestems always constitute a larger fraction of the marsh. Means and 95% confidenceof total biomass,interval s are plotted.

plant growth, whereas deposition on previouslywaterlogged fine sediments awayfrm the mouth actually made an improvementby raislng the marsh surfaceslightly, thus reducing water1 ogging andallowing better aeration of roots (Onuf etal. 1981b), These changes may indicate aNEmechanism for succession due to stonn-c sediment deposition, an interpretation.- cnsupported by one other observation: Jaumeag carnosa, a high-marsh plant, invaded thePlow marsh in one location during thisv- mstudy, suggesting an increase in elevationInat that site,Inm5.-mThe Upper Marsh Vegetation0 1000Distance from mouth (m)Figure 28. An il lustration of the years xlocation interaction on the biomass ofSalicornia vir inica in the lower marsh atMugu Lagoon h a n s for the six locationsprogressively farther from the mouthof the lagoon for 1978 through 1981; (b)expressed in the form of linear regressions.in 1978 over 1979 as a stimulation ofgrowth by the major storm of February1978, followed by a return to "normal"conditions in 1979. Presumably, the stormstimulated growth either by reducing thesalinity of the soil or by addingnutrients via the thin layer of sedimentsit deposited. This interpretationremained ger~erally tenable in 1980 withits major storm, However, short-termstimulation was not the explanation forthe biomass increases seen in 1981, whichhad no major storm.Some evidence suggests that the depositionof sediments by storms in the easternam may have had opposite effects, dependingon the site and its prestorm characteristics,Deposition of new finesediments on what had been a well-drained,re1 atively sandy substrate near the mouthapparently made it less suitable for marshAll information on the upper marsh isfrom one area located approximately halfwaybetween the mouth .and the easternterminus of the lagoon. Extensive preliminarysampling indicated that this part ofthe marsh was representative of a1 1 of themarsh surrounding the eastern arm of thelagoon in percentage cover of the cmmonspecies,Perennial pickleweed is the major contributorto biomass of the upper marsh(Figure 29), but the upper marsh is not amonoculture in the way that the lowermarsh is. Based on the overall annualaverage for ten samples collected eachmonth, perennial pickleweed (Sal icorniavirginica) accounted for 44% of total biomass;sea lavender (Limonium cal iforni-- cum), 21%; a1 kali heathiinia jrandifolia), 15%; Jaumea carnosa, 14%; sal twort7ZZi-s marit- r a n d arrowgrass(Tri lochin concinnum), 2%. The Go othersjEZkF7hat were collected togetheraccounted for less than 1%: sea-blite(Suaeda cal ifornica) and annual picklewm a l icornia bigelovi i), The flora ismore diverse than that of the lower marshbut still is relatively simple.It might be expected that a more variedflora would result in a more even distributionof biomass over the year, sincedifferent species would reach peak biomassat different times. This is notevident from Figure 29. The maxima in Mayand July are twice the minima in Januaryand December, partial ly because specieswithout overwintering woody parts, Jaumeaand Triglochin, are present. The erratic

100Jaumea carnosaTriglochin concin~umFigure 29. The bicmass of canmon plants of the upper marsh at Mugu Lagoon indifferent months, 1977, mean of ten 0.06-m2 samples each month,

fluctuations in rrozt species car! be ?;ap?ained by patchiness, The fiior-* cdri omoutcane is that Sat i~orrtia v-i ryj rljca -- kiomassimre strorlgfy=a%nal dt ehizelevation than in the low~r i-~ai"c,ti, prlrllar~~~because of the sl ightly di fferpnt 31 10~dtionof biornass betwe~ri woody r)arfc, andgreen growing tips. Over the year a? awhole, the bimass of woody parts is 4,9tirrtec, that of green partr in the lowermarsh, as ccxnpdred to 3.6 in the uppr%rluarsh. Thus, the highly seasonal cmlponentof perennial picklewced (the qrernshoots) is proportionately greater in theupper riktrsll, but wc have nn idcla why.In the previous sec ti an, ycar-to-yearchanges in the bicrn;a

Fran understanding the rrxchani sms thatbring about these changes, Also, we doriot know how applicable this descriptionfor the eastern ann is to the larger expanseof salt marsh in the western ann.Casual observations indicate that the twoareas of marsh are similar floristical ly,but that the vegetation is denser andtailer in the western am. On a largerscale, the Mugu Lagoon salt marsh differsgreatly fran the better-known sal t marshesof the east and gulf coasts. Instead ofdominance by grasses such as Spartina- a1 terniflora, 2. patens, and Juncus roemerianusas in the eastern United States,succulent halophytes such as the - Salicornias,Jaumea carnosa, Batis martima,and ~uaedamfornica, andothermorphologically canplex plants such as Limoniumcal i fornicum and Frankenia grandiflorareva ail. Local and interreqional canpari-kens will be pursued further in Chapter 6.4.2 THE INVERTEBRATESThere has been no survey of zooplankton,a1 though, 1 i ke the phytoplankton, they areprobably primarily marine species: copepods,cl adocerans, os tracods, arrow worms,and planktonic larvae of the benthicinvertebrates (Macdonal d 1976b). Study ofthe invertebrates of Mugu Lagoon has beenintensive but selective. With the exceptionof the MacGinities' (1969) brief summaryof the biota of the whole lagoon,Wolfe et al.'s (1979) analysis of 12samples for the western arm, and specieslists compiled from 5 areas in and aroundthe central basin in 1980 and 1981 (SoilConservation Service 1983), reports arelimited to the eastern arm. The taxa,preponderance of small species, and highdensities (30,000 per inn) reported byWolfe et al. (1979) are characteristic ofthe mudflat environments studied ingreater detail by Quammen (1984) in otherlocations and are consistent with thefine-sediment, 1 ow-energy environmentattributed to the western arm in Chapter3, based on suwerficial observations. Inaddition, high 'densities of Tryonia imi ta-- tor, a small brackish-water gastropod, inthe far western end of the western arm areconsistent with the prediction in Chapter2 that freshwater inputs would have theirgreatest influence there. The sampling ofthe central basin was sampled after mstof the subtidal area had been filled bythe major storms of 1978 and 1980 (Figure14). The large number of insect taxareported (Soil Conservation Service 1983)indicates a large influence of Cal leguasCreek under the present conditions.Mi thin the eastern arm, macroinvertebrateswith hard parts - crustaceans,echinoderms (sand do1 lars) and especial lymollusks - have received a great deal ofattention. However, even here, coveragehas been uneven. Only Macdonald (1969)sampled wi thin the sal t marsh, whereasWarme (1971) sampled most types of tidalflats and to a lesser extent subtidafareas, and Peterson (1975) only sampledthe subtidal sand channel. Warme (1971)recognized two major assemblages: "thesand-channel fauna" and "the mud-tolerantfauna" of the inner lagoon. Smith (1981)studied the distribution of ciliated protozoansalong the sandspit shore of theeastern arm. Smith (1981) found littleevidence of habitat differentiation byprotozoans with respect to the environmentalgradients that he distinguishedalong the sandspit, probably because thedifferences in sediment characteristics,temperature, and salinity between samplesites were small compared to other studieswhere habitat differentiation was reported.Abundances were comparable tothose reported by other workers and werehighest in the finest sediments before themajor storm of February 1978. After thedeposition of large amounts of mudthroughout the lagoon, abundances werehighest in the coarser sediments near themouth, presumably because the organic contentincreased whi 1e pore space remainedhigh. Away from the msuth, the organiccontent increased, but pore space diminished(Smith 1981).These data are too restricted to serveas the foundation for this chapter, Instead,we base most of the following onour previously unpubl ished invertebratedata. The advantages are that we sampleda1 1 physiographic units except tidalcreeks and salt pans (Figure 32a); includedthe "soft" invertebrates, mainlypolychaete and oligochaete worms, phoronids,si~unculids (peanut worms), andholothurians (sea cucumbers), as we1 1 asthose with hard parts; and spanned themajor stonns of February 1978 and 1980 for

Figure 32. (a) Locations saatpled qrrarterly for invertebrates in the easternam of Mugu Lagoon in 1977. (b) rites grouped according to 50% similar1 ty indensities of mjor catqories. and (c) m an densities of those categories in

two areas (Yransects 2 and 3, Figure 32a).In subtidal areas and fntertidal flats,the samples consisted of all material retainedby a 3-m screen (Transects 1 and2, the sandy areas) or a l-mm screen(Transects 3 through 6, the muddier areas)excavated from within a steel cylinder1/16 m2 in cross-sectional area to a depthof '~50 cm. Within the marsh only theepifauna were recorded from the 1/16-m2samples collected as part of the plantproductivity studies. Invertebrate samplingdid not address zooplankton andmicrofauna. Despite these omissions, thesimilar methodology for all tidal flat andsubtidal areas a1 1 ows comparisons betweenlocations and years for similar kinds oforgani sms.Dupl icate quarterly samples were canbindfor each site (Figure 32a), and theaverage annual density of each taxon wasdetermined. The taxa were grouped intoeight morphotype categories : large andsmall worm-1 i ke organisms, 1 arge and smallgastropods, large and small crustaceans,bivalves (large), and sand do1 lars(1 arge). Large and small correspondroughly to scales of centimeters and millimeters,respectively, for the largestdimension of the most common size classesof each taxon. Table 4 indicates theTable 4. Mean density of invertebrates (number/m2) in 1977 for all sites sampledin the eastern arm of Mugu Lagoon. For Transects 2 & 3 combined, mean densitiesare reported for 1977 and 1978-80. Indications of responses to storm-causedalterations of the study area are also given. See the text for a description ofthe sampling procedure and Figure 32 for locations sampled. p = present at 5 per m* on at least 1 transect in at least 1year to be listed individually.Transects 2 & 3A1 1Down alltransects 3 years N oInvertebrates 1977 1977 1978-80 after storm Gone change UpMean density (no./m2) Population response to stormsLarge Wonn-1 i keNotomastus tenui s 307 775 330 x~ap1 oscol op-onga tus 58 7 3 xPhoronid 47 108 23 xPareurythoe cal i fornicaNemerteanHemi podus boreal isGoniada sp,WSD.Axiothel ia rubracinctaSi puncul idophel iaTotalSmall Wonn-1 i keLep tosynap ta a1 bi cansSabellid sp.spi ophanes. mi ssionens is01 igochaete sp.Minus pi o ci rri feraCapi tel la capi tataPolydora sp.Streb'iospio benedfcti(continued)XXX(Large numbers 1 year) ?(Never present)X(Never present)(Large number storm years)x

Table 4. (Concl uded) ,. .. .transects 3 years NoInvertebrates 1977 1977 1978-80 aft& stom Gone change UpMean dens? ty (no./m2)Population response to stomsSmall Worm-1 i ke (continued)Armandi a brevi s 7 9 PPseudopol-sp. 302Total 516 479 709Large Gastropods~eri thidea cal i forni caWlma taCrepPdu'laTotalSmall GastropodsActeocina spp. 185 371 668Assiminea calf fornlca 128Total 18 5 371 796Bi val vesLarge crustaceansCal lianassa cal iforniensis 98 123 45Hernlgrapsui ore onensf s 13 11 12+I 112 136 60Small crustaceansGammaridean arnphi pod 28 5 15 (Large numbers 1 year)Caprell id arnphi pad 19 5 240Cumacean 2 4 P 21Total 7 4 11 276Sand do1 JarsDendraster excentricus 2 4Total 2 4

taxonomic composition of the differentcategories by listing the dominants ofeach category,Sites were grouped based on the criterionof > 50% similarity in densities ofthe different categories of invertebrates(Figure 32b). Three patterns are evidentimmediately: (1) The groups were separatedprimarily according to distance fromthe mouth of the lagoon; intertidal versussubtidal distinctions tended to be lessimportant. (2) Densities were lowest atthe ends of the lagoon (Groups 1 and 6)and around an order of magnitude higher inthe middle (Groups 3 and 4). (3) There1 a tive importance of large taxa decreasedwith distance from the mouth.Another pattern cannot be extracted fromthis analysis but is important, nonetheless:filter feeders dominated the sandchannel and deposit feedel-s dominated theponds.Generally, sediment characteristics areconsidered the best diagnostic characteristic of the associated invertebrate assemblage.According to the 1977 (prestomi)data, the invertebrate fauna ishighly differentiated according to locationwithin the eastern arm, yet sedimentsdid not appear to be differentiated to acorresponding degree. Thus, the bottom ofthe lagoon was sandy in almost everysample collected from subtidal areas andintertidal flats before 1978 (Warme 1966;Shaffer and Onuf 1983; Shaffer and Cermak,unpubl. observ.). Silts and clays approachedan equal share with sand in themiddle of the ponds, while sand predominatednear the invertebrate-sampl i ng sitesat either end of the lagoon. Despite thesimilarity in sediments and the simil aritiesin total density of invertebratesbetween east and west ends of the easternarm, these locations diverged more in there1 ative abundances of different morphotypecategories (as indicated by the largeinvertebrate to small invertebrate abundanceratio, for instance: 65:l at thewest end as compared to 1:14 at the eastend; Figure 32c). Obviously, some otherfactor besides sediment texture is involved.The changes after the storm of1978 will explain some of this fine discriminationamong apparently very similarhabitats and the difference between endsof the lagoon.Figure 33 presents the same kind oftreatment of the data by category ofinvertebrates as Figure 32 but for differentyears in the same location (sandybottomchannel and subtidal pond), ratherthan different locations in the same year.The response of the invertebrates in thesand channel to major but brief episodesof reduced sa1 inity and burial by finesediments has been a continuing reductionof abundance experienced almost equally byall qroups (Fiqure 33, channel). The sanddo1 lar dendras-ter excentricus was an exceotion.It was eliminated from Mugu~a~oon by the storm in 1978. ~lthoughsmall individuals were seen occasional lyafterwards through 1980, they were notfound in any samples. By the end of 1982,large-sized Dendraster again were abundantin the sand channel, only to be eliminatedonce again during a period of heavy rainsin January 1983.The responses of the invertebrates tothe long-lasting alteration to fine sedimentsin the westernmost pond of the easternarm were similar to changes in thesand channel only in the persistent reductionof the 1 arge worm-1 i ke organi sms(Figure 33, pond). Otherwise, the responseswere large changes in the relativeabundances of di fferent categories of invertebratesbefore and after the February1978 stonn (in which smal ler invertebratesgenerally were favored) and great annualvariability after the storm.The responses of individual speciesprovide more insight into these largescalepatterns and fluctuations (Table 4).The small worm-1 i ke invertebrates respondedmost strongly to the transformationof the bottom. Three species thataccounted for 97% of all individualscollected on Transects 2 and 3 in 1977were eliminated and have not been collectedsince: Leptosynapta a1 bicans (ahol othurian) , Spi ophanes mission ens^ s, andan unidentified sabel lid polychaete. Intheir place appeared three other specieswhich were not co1 lected in 1977. Thesethree species accounted for 77% of allindividuals collected from 1978 to 1980:paucibranchiata and Capibothpolychaetes, and anunidentified species of oligochaete.Pseudopol ydora was not col lected anywherein the lagoon in 1977; however, the others

CHANNELGASTRQPODSCRUSTACEANSWORM-LIE- XXX>-m-NUM E3ERM2Figure 33. Changes in densities of invertebrates from 1977 to 1980. Sites havebeen grouped by the crlterfon of 50% similarity in the densities of the indicatedcategarf es.had been cannon at one or two sltes near the stonns, especially in the stom yearsthe eastern end of the big pond (Transect of 1978 and 1980.4). Strebyspio benedicti, a plychaetr,was the on y species present in the area In the other categories of mall inverin1977 that was much more abundant after tebrates, taxa already present or abundant

in the area became more abundant, Thesmall gastropods f Acteocina spp.) a1 mostdoubled in numbers. Numbers of varioussmall crustacean species have been largebut highly variable among different sitesand in different years.The most abundant large invertebratesexhibited yet another response. Theydecreased in absolute abundance, but theychanged 1 ittle in relative abundance.Dominant species remained dominant afterthe storm,Among some species of low or intermediateabundance, differences before andafter February 1978 were consistent withdifferences in preference of muddy conditionsinferred from distributions in 1977.Thus, the bamboo worm (Axiothella rubra-Ycincta) was col lected almost exclusivelyin the sand channel in 1977 and was notcol lected afterwards. The clam Nuttall i anuttallii, only seen in the sand channelin 1977, was not collected at all from1978 to 1980. The clams Macoma nasuta andProtothaca staminea were re1 ativel yabundant in muddy areas in 1977 and didnot decline. However, there were counterexamples: the "mud intolerant" clamDiplodonta orbel lus of Warme's (1971)analysis did not decline (refuting mudintolerance), nor did the polychaetePareu rythoe ca1 i fornica previously foundexclusively in the sandy-bottom channel.Other species associated primarilywi th mddi er areas did decline or di sappear:the clam Chione (two species) andthe polychaetes m a sp. and NereisTwo factors seem to be most importantfor interpreting these responses. First,the infaunal elements that inhabited thelagoon in 1977 were affected adversely toa greater extent than epi4 aunal elements.Second, small invertebrates responded morestrongly, whether positively or negatively,than large invertebrates. Theseinfaunal -epifaunal and large-smal 1 di s-tinctions appear to be much more informa- SPtivethan faunal -si te associations ininterpreting the responses of the invertebratesto the storm-caused a1 terations There is a simple explanation for atof the lagoon. Our genera1 expectationleast part of this counterintuitivewas that those taxa most closely allied result. As illustrated in the previouswith the muddiest habitats in 1977 wouldchapter, no place in the lagoon was trulybecane more widespread and abundant aftera mud bottom in 1977; i.e., sand predomithetransformation of most of the lagoonnated at all stations sampled. Sinceto muddier condi tions. Conversely, we1978, the mud fraction has becme asexpected the taxa most closely a1 lied with predominant as the sand fraction wasthe sandiest habitats in 1977 to suffer before 1978. Apparently, the new finemost, perhaps then recovering rapidly onlysubstrate was as novel and foreign for thein the sand channel. Instead, the mostpreexisting fauna of the ponds as it wasprominent of the muddy associates disapforthe fauna of the sand channel. Thepeared and were replaced, and the mostsedimentation probably affected the pondprominent of the sandy associates havefauna more because it lasted longer ordoggedly persisted, even in the area thataffected those organisms more di rectf y.is verv muddy now. For examwle, . - the pol v-For instance, the anaerobic layer probablychaete" ~a~liscol oplos el ongatus and thelay much closer to the surface after theholothurian Leptosynapta albicans stronglyfine sediments were deposited. This woulddominated the lame and small worm-likebe much more stressful for a very smallcategories, respeGively, at the muddiestorganism that relied on gas exchange withsite in the lagoon in 1977 (Site 2, Traninterstitialwater than for a largesect 4, Figure 32). Both were present onorganism like the ghost shrimp Calli-Transect 3 then. Neither was col lected inanassa, which pumps large amounts of water1979 or 1980. On the other hand, Notomafromabovethe sediment surface throughstus tenuis, the dominant large polychaeteits burrows.both-ndy areas and on Transect 3 in1977, survived in both wlaces, as did the The effects of the storm also provide aghost shrimp (~allianaska californiensis) partial answer to the question posed earandits commensal clam in sandy areas, lier sf why such a narrow gradient ofCryptomya californica.sediment types could yield such a highly

differentiated assemblage of invertebrates.The relatively uniform sedimenttypes in I977 were a reflection of a uniformsediment source, not a rnonotonousdepositional or hydrodynamic regime. %ensediments that could be differentiatedfinally were supplied in 1978, they Heredifferentially distributed (Figure 15).Obviously, the invertebrate biota had beenresponding to the varied hydrodynamicregime, rather than to differences inseditnents. Now, there is a broad spectrumof sediments as we1 1 as depositionalregimes.The salt marsh 1s an unimportant habitatfor invertebrates relative to the adjacenttidal flats and subtidal areas; however, afiw species can t>e abundant in someplaces. They are the gastropod Cerithideacallfornica and the crab Pachycrassipesin the lower marsh, and the gastropodolivaceus in the uppermarsh.is rmch smaller and probablyundant than Cerithidea.Nacdonal d (1969'1 reaorted another qastro-pod,~ssidnea . cali fornica, to & muchmore 3- t w i d e a . We sawlarge numbers of ~sslminea In the lagoonin 1980 but few in the sart marsh at anvoccupies burrows ins very active on the tidalflats east of Transect 3 (Figure 32) atlow tides frm Aprll to Septetnber, Cerithideahas been abundant in the marfitG c t 3 throughout our study. Since1978 it has expanded onto the mudflats onTransect 3, became proy ressively moreabundant 1978 through 1980 at the marshplant sarnpl ing site ha1 fway between Transects3 and 4, and appeared in the marshat Transect 4 in 1979 and 1980.4.3 THE FISHESThirty-nine species of fish have beenidentlfi ed frmn Nugu Lagoon; ha1 f the speciesare common (MacGinf tie and MacGini tie1969; Baker 1976; Onof et al. 1979; Onufand Quammn 1983). Only MacGinitie andMacEini tie (1969) and Baker (1976) sampledthe three major divisions of the lagoon.Bath sources reported fish as least abundantin the western a n and attributedthis rarity to the severe restriction oftidal exchange in this part of the lagoon."Rare or accidental marine species" (Baker1976) were mostly in the central basin, asmight be expected for strays From ooencoasthabitats, because of the location ofthe mouth and the prevalence of deep, openwater in the central basin when theseobservations were made e , before19 78)-The four mst canmn species in thelagoon are all small : arrow yobies(Clevelandia ios) inhabit the burrows ofcrabs and ghors hrimp; topsmel t (Atherifiopsaffjnis), occur in dense schools inthe water column; staghorn scul pin(Leptocottus amatus) rest on the bottcmmost of the time; and shiner surfperch) are in denseThe arrow goby,topsmel t, and staghorn sculpin are widespreadin the laqoon and can be found allyear, *ereas fhe shiner surfperch islocalfzed in its occurrence and highlyseasonal . Sharks, rays, and the shovel -nose gui tarfi sh (Rhinobatos productus),a1 1 elasrrtobranchs, are the only fish cmrnon-in the lagoon as large individual%.More detailed infomiation Is availableon fish using the eastern ann of MuguLagoon (Onuf and Quanmen 1983). Wesampled the fishes of the eastern arm ofMugu Lagoon by beach seine monthly at foursites from February 1977 to February 1982.We selected the sites to represent therange of rnajor habitats avhilable to fishand to contrast physiographic and vegetatfondlfeatures (Figure 34) : shal low(Sites 1 and 2) vs. deep (Sites 3 and 4),and vegetated (Sites 2 and 3) vs. bare(Sites 1 and 41, There also was a gradientin sediment texture: fine fractionincreased frm Site 1 to Site 4, Thesesites encoinpassed most of the range ofenvi ranmental conditions that might infl u-ence the kinds and abundances of fishespresent. Habitat types not sampled includedmarsh channels, the rfiarsh itself,and the shallow subtidal area at theextreme eastern end of the lagoon whichdiffers from the shallow sltes that wesampled by having almost no tidal current.Thirty-five species were caught in thefirst year of samplinq. Two species, topaFfinis)and shineraqqregata) accountedfor over three-guarters of allindivfduals caught, The eight most common

Figure 34. Fi sh-sampl ing sites and their characteristics in 1977.species accounted for 96% of all individualscaught, Data from the 9 months whenall stations were sampled indicate thatdepth and cover by eelgrass were equallyimportant as determinants of fish abundance.Catches were least in the shallowbare site; more than twice as great at theshallow, eelgrass, and deep bare sites,and more than twice as great again in thedeep, eelgrass site (Table 5). Apparently,depth and cover by eelgrass interactsynergistically for a number of species,since the difference in total speciesbetween eel grass and bare sediment wasmuch greater at the deeper sites thanthe shallow ones: 23 vs. 15 as compared to12 vs. 11, respectively. It cannot bedetermined from these data whether thedi fferences in substrates between sites(Figure 34) contribute to the observedpattern.All the common species were found at allthe sites; however, seven of the eightspecies making up 98% of the total catchwere caught at least 75% of the time ateither one or two sites (Table 6). Thespecies were relatively evenly distributedamong categories of habitats: threesingle site associations, each with a differentsite, and four associations with apair of sites, each with a different pair.The most common spec1 es - topsinef t andshiner surfperch - were found at the deepstations, the surfperch at the vegetatedstation and the topsmelt at both the bareand vegetated deep stations. Fish caughtmore often in the shallows included thelongjaw mudsucker, the California kill i-fish, and the bay pipefish.A strong seasonality is evident in the5-year averages of total monthly catchesand for catches of individual species(Figure 35). Most have been caught inevery month of the year, but many werevery rare at least for a couple of thewinter months. The June peak in totalcatch was not the result of the abundantspecies behaving similarly, but ratherrepresents large numbers of the two dominantspecies, topsmelt and shiner surfperch,being present at the same time.For the species in general, the overridingimpression is that the peaks in abundanceof individual species were remarkablyspread out over the year: essentiallytwo peaks per month from April toOctober (Figure 35). Perhaps this is anindication that the resources of thelagoon are being partitioned temporally aswell as spatially. Alternatively, it mayreflect only differences in the temperaturepreferences of the different species.A1 though nearshore fisheries are variablewith respect to time (hours, bays,months, and years) and place, three factorsallowed us to rigorously analyze the

fable 5. Total catch of fishes by species and site in the 9 months af 1977 when allsites were sampled. The percentage contribution of each species to the total at allsites is alsn shown at the far right. Cmmon names fol low Miller and Lea (1972).Site character4 sticsShall owDeepSpecies Bare Eel grass Bare Eel grassCanmon name Scientific name (Site 1) (Site 2) (Site 4) (Site 3) %Topsmel tShiner surf perchStaghorn scul pinCalifornia kil lifishDi amond turbotBay pipefishCal i fornia ha1 i butLongjaw mudsuckerBay bl ennyCalifornia tonguefishGiant kel pfi shKelp bassBrown rockfishOpa l eyeShovelnose gui tarf i shGrey smoothhoundBlack surfperchKelp rockfishBarred surf perchPacific herringKelpfish 2Kelpfish 3Round stingraySpeckled sanddabBarred sand bassStriped mu1 letStarry flounderSpotted turbotLeopard sharkTotal individuals (all%Urol ophus ha1 l eriMu 11 cephalusFhrhis stel latusP euronlc th s ritterib s c i a t astations = 5,460)Total species (all sta tions = 29)effects of the major stonns of 1978 and1980 (Onuf and Quammen 1983). First,sampling at the same site monthly for 5years was frequent enough to identifysystmatf c di fferences betwen years bynon-parametric statistical procedures,even when the high seasonality and aggregateddistributions of the fishes madestandard parametric statistics inappropriate.Second, the storms affected thefour sites differentially, some rrarch moreseverely than others. This allowed testsof the fa1 lowing sort: if differencesbetween years were the result of thestonns, then bigger changes should beassociated with the more severely affected

Table 6. Habitat characteristics of the common species of fishes inMugu Lagoon tnferred frm features of the sites at which they werecaught most frequently.Shal lowDeepBare Eel urass Bare Eel urass(Site 1) (siee 2) (Site 4) (site 3)>75% caught at one siteShiner surf perchCalifornia ha1 ibutLong jaw mudsucker>75% caught at two sitesTopsmel t x xStaghorn scul pin x xCalifornia killifish x xBay pi pefish x xsites. Third, the symmetrical sequence ofminor and major storm years for the 5years of sampling (minor-major-minormajor-minor)from February 1977 to February1982 permitted the strongest possibleinferences about the effects of storms.Not only was there replication of thebasic comparison between the years immediatelyfollowing major storms and years atleast 1 year removed frm major storms,but a1 so there was the opportunity to di s-criminate between short-term effects (comparisonsbetween adjacent years) andpersistent effects (comparisons betweensequenti a1 stonn years or nons tom years ).The analysis is beyond the scope of theprofile and is reported in Onuf andQuamen (1983), but the concl usi ons werestraightforward.A1 1 significant differences betweenyears indicated storm-caused declines inthe total catch for the whole lagoon andin the total number of species caught inthe eastern arm as a whole. Part of thereductions were short term, since increasesinvariably ensued after each majorstorm year (Figure 36); however, part ofthe reductions were persistent, and overallthere were almost 50% fewer fish in1981 than 1977.The decrease in depth and virtual eliminationof eelgrass at all sites withinthe pond had a cascading effect on thesuitability of different sites for differentspecies, The originally shallow,half-eelgrass, ha1 f-bare Site 2 becamealmost entirely intertidal and bare, Theoriginally deep, bare Site 4 became mostlyshallow. The originally deep eel grassSite 3 became bare and shal lower, butstill was deep in relation to other sites.The originally shal low, almost entirelybare Site 1 did not change in depth butsubstantially increased in eel grass cover.Species swi tched locations accordingly,and those for which no analog of theirfavored habitat existed at the end of thestudy declined in abundance (Figure 37),The deep-waterhabitats of the originaldominant species - topsmelt and shinersurf perch - were el imi nated. Topsmel t(79% caught at the two deep sites in thefirst year) were down 57% in the fifthyear compared to the first, and shinersurfperch (80% caught at the deep eel grasssite in the first year) were down 97% frmthe first year to the fifth. Our initialexpectation was that species that spentmost of their time on the bottm wouldrespond very strongly to the new, finetexturedbottom. We expected thosespecies (California halibut, didmond turbot,staghorn scul pin) associated withSite 4, the muddiest area during the firstyear, to prosper, and those associatedwith a much sandier area (California

Total catchlo00SPLCKUD IANDDADlAMOND TUffOOTITAOHQIN SCULPlNSHINtl SURrPERCHCtWIPOUMtATQWOYllrtSnarr PlrtFtrnFigure 35. The 5-year average rtrcrnthly fish catch at Mugu Lagoon, arranged by month ofpeak abundance, from earliest at Lop to latest at bttam.

ddving ducks (mainly mol lusk eaters, 15%) ;large, long-bi1 led shorebirds (probingfeeders, 13%); gulls (11%); wading, diving,and aerial fishing birds (6%); anddabbling ducks and geese, (mainly planteaters5%). The category "other" containedmostly strays plus the Americanbittern (seen mainly in the marsh, feedingon insects), ki 1 ldeer (seen mainly supratidallyon the sandspit shore of thelagoon, feeding on insects), and Northernphalarope, a shorebird relative that feedson plankton.Figure 36. Changes in mean monthly fishcatch and mean number of species caughtfrom 1977 to 1981.kil li fish, longjaw mudsu~ker) to suffer.If sediment type had any role in determiningnumbers and distribution, it was overwhelmedby the effects of depth and coverby eelgrass.4.4 THE BIRDSNo quantitative bird census data havebeen published for Mugu Lagoon. The NaturalResources Management Office, Pt.Mugu Naval Air Station, CAY has compiled a1 ist of 198 species found on the Air Stationin both wetland and upland habitats(unpubl.). The following analysis of thedistribution and abundance of waterrelatedbirds in space and time is basedon censuses of 21 areas conducted at 20-day intervals near the predicted time ofthe daylight low tide from October 1977 toSeptember 1982 (Quammen and Onuf, unpubl.data). Census areas were limited topermanent open water and intertidal flatsand were located in the western arm andcentral basin, as we7 1 as in the easternarm.An average of 2,700 birds was countedper census (Table 7). In a1 1 , 73 specieswere seen during the study; 8 species wereobserved at more than 100 per census andaccounted for more than 70% of the total;and 16 were observed less than once in 10censuses. The general ly small, surfacefeedingshorebirds were the most abundantcategory (33%); followed by coots (16%);There is a strong seasonality in thetotal abundance of birds in Mugu Lagoon,as indicated by the monthly averages forSites 1 through 20 (Figure 38). In Mayand June, 100 to just over 200 birds werecounted per census. From July through'ieptember, numbers were close to 1,000 andfrom October through April were between2,000 and 4,000. December, January, andFebruary were the months of highest abundances,yet only coots and diving ducksreached their maxima in this period. Apparently,Mugu Lagoon is a southern tenninusand overwintering area for thesemigrants. The fish-eating birds showedspring or fall peaks, and in the extremecase of the aerial fishers, had theirlowest numbers in the winter. This isconsistent with the much higher abundancesof fish in the spring and fall (Figure35). The wading and diving fishers, however,go elsewhere in the summer when fishare most abundant.The remaining groups had varied seasonalpatterns. The probing shorebirds weremost abundant in winter and least abundantin May and June, but varied less over thewhole year than any other category. Therelatively high numbers of surface-feedi ngshorebirds and dabblers present in midwi n-ter suggest that some overwinter in MuguLagoon; on the other hand, the appearanceof some in early autumn and greatest abundancein March or April indicate thatothers migrate through to overwinterfarther south. The fa1 l-spring asymmetryof abundance suggests that the southwardmigration is much less synchronous thanthe return north as has been noted forsome of these species by Recher (1966) andPage et a1 . (1979),

Babie 7. Abundance ranking and mean number of birds seen per censusaveraged over all seasons, 1977-82, for 21 census sites (see Figure 39)in Mugu Lagoon. abundances are given by species and functional category;species are listed in decreasing order of abundance within a category.Rank and site where most commonly observed are a7 so listed.Rank in abundanceCategorySpecies1 SURFACE- FEEDING SHOREBIRDS2 Dowitchers spp.3 Western sa9dpi per7 Sandpipers8 American avocet13 Dunlin21 Least sandpiper22 Sander1 i ng28 Black-bellied plover36 Stilt39 Semi pal mated plover47 Snowy plover52.5 Red knot57.5 Wilson's ploverBlack turnstoneRuddy turnstoneSurf bi rdWandering tattlerNumber seenper censusSitewhere mostoften seenPROBING SHOREBIRDS 354.45 Marbled godwi t 200.89 Willet 140.533 Long-bil led curlew 9.342.5 Greater ye1 1 owl egs 2.254 Whimbrel 0.61 COOTS 428.0DABBLING DUCKS & GEESE10 Northern shoveler18 Northern pintail19 American wigeon31 Cinnamon teal37 Green-winged teal50 Mallard52.5 Canada goose55 BrantGadwallDIVING DUCKS4 Ruddy duck11 Susf scoter(continued)

Table 7.(Continued),Rank in abundance'CategorySpec1 esDIVf NG DUCKS (continued)15 Canvasback16 Greater scaup27 Whi te-wi nged scoter35 Buff leheadRed headGo1 deneye9 WADING FISHERS34 Snowy egret41 Great blue heron48 Great egret8 DIVING FISHERS24 Western grebe25 Double-crested cormorant30 Red-brested merganser40 Eared grebe46 Pied-bil led grebe49 Horned grebe56 Common loon57.5 WhJ te pelicanArctic loanRed-throated loonAERIAL FISHERSBrwn pelicanForster's ternCaspian ternRoyal ternElegant ternLeast ternBe1 ted ki ngflsher5 GULLS6 Ring-hi1 led gull12 Calffornia gull17 Western gull26 Heemann's gull32 Bonap$rt@ gull38 GullsGI aucous-wd nged gu? 1Nu~iber seenper censusSitewhere :nostoften seen10 OTHER 3,042.5 Northern phalarope 2,251 Ki1 ldeer O.abAmerican hi ttern

Table 7. (Concl uded) ,Rank in abundanceCategorySpeciesNumber seenper censusSitewhere mostoften seenOTHER (continued)bWhite-faced ibis ~0.1Black oystercatcherFlamingo (sp. ?)Roseate spoonbill:seen from too far away to identify the species.Species seen ~0.1 per census not ranked.Bird abundance varied among sites de- Then characteristics of sites were soughtpending on functional category, yet we that were shared in common within thehave been largely unsuccessful in explain- group but differed from other groups.ing the abundance patterns based on sitecharacteristics. Instead, we turned theprocess around here, as with the inverte- The census sites formed six distinctbrates. Groups of sites were defined by groups according to the criterion of >60%>60% similarity in their densities of the similarity in the densities of ten catecategoriesof birds designated in Table 7. gories of birds (Figure 39; Table 7).4000200Probing shorebirds"Aerial fishers100n500J A S O N D J F M A M JFigure 38. Five-year average abundances of water-related birds by month at censussites 1 through 20, Mugu Lagoon (Figure 39), arranged according to month of peakabundance from earliest at top left, to latest at bottom right.

Group #: 1 2 3 4 5 6Coots 18.2 10.1 0. 1 0,1 (1.8 1.1Surface-feeding shorebirds 29.2 10.9 1. 3 3. tj 5 1Dabbling ducks and geese 4.3 1. 2 1.9 2 0.8Prabi ng shorebirds 6.0 3.8 5.0 10.8 7 4 4.1Wading fishers 0.2 0.1 0.1 0 2 0 ? 0 2aivi ng ducks 5.5 1.3 Y 0.2 0 4 3 9 u. 6Diving fishers 0 5 1.3 0.1 0.3 0 9 0.2Aerial fishers 1.6 0 5 1.3 0 6 0 1 0.1Gui Is 2.2 Q. 9 6.4 1. H 0 6 0.1Others 0.1Total birdslhaFigure 39. Bird census sites grouped according to >60% similarjty in their densitiesof the indicated categories of water-related birds and the rnean densities (no./haj ofeach category in the different groups of sites.

According to these site associations,the salient features of habitats are asfo1 lows for the different categorSes ofbi rds. Coots and surface-feeding shorebirdstend to correspond in their selectionof habitats and favor sites withlarge expanses of mudflats and shallowopen water, Presumably, the coots aresomewhat more closely tied to the water inthe mudflat-open water habitat and feedprimarily on the sometimes thick mats ofEnteromorpha; the surface-feeding shorebirdsare [nore strictly confined to thetidally exposed portions and feed exclusivelyon small invertebrates on and justbelow the surface of the mud, The lowdensities of invertebrates that we documentedfor the extreme eastern end of thelagoon may explain the relatively low density of surface-feedi ng shorebirds inGroup 1; however, this is speculation onlysince a l-mm screen is too coarse tosample the prey of the birds satisfactori1 y.The dabblers were most abundant at sitescontaining islands covered by marsh vegetation.Their distribution deviatesstrongly from that of the coots, whichalso dabble most of the time.The large, deep-probi ng shorebirds andthe wading fishers (egrets and herons)were similar in their relatively evendistribution throughout the lagoon (Figure39). Both categories are birds of thewater1 ine. Apparently, whether a shore issteep or flat is of little consequence tothese birds since they spend most of theirforaging time close to the water's edge.The probing shorebi rds are therefore di s-tinct frm the surface-feeding shorebirdsin terms of a more linear vs. more arealdispersion. In addition, they are preeminentlythe birds of sand flats andsandy shores. While most other feedingtypes are rare here, the probing shorebirdsare at their most abundant, as arelarge, deep-living infauna, their preferredprey.The largest expanses of open water attractedthe greatest numbers of divingducks and diving fishers (Figure 39). Thediving ducks feed mostly on invertebrateson the bottom. Ducks such as meryansersthat dive for fish in the water colurnn oron the bottom are classified with theother diving fishers (the grebes, loons,and cormorants). Gulls and the aerialfishers (mostly pelicans) were most commonroosting on sandy islands near the tidalinlet. These they shared with hauled-outharbor seals. The aerial divers, in thiscase mostly terns, a1 so roosted on anothersmall island in Site 17 and a sand bar inSite 7 (Figure 39). Although terns, pelicans,and gulls feed inside the lagoon, wedo not know how much foraging is doneel sewhere.There is little indication of long-termchange in the total number of birds uti-1 izi ng Mugu Lagoon based on our 5 years ofrecords, a1 though numbers were somewhathigher in the last 2 years than in previousyears (Figure 40). Within categories,much larger changes are evident.For example, in the lagoon as a whole thenumber of coots has declined every yearsince 1977-78 (59% in 5 years). In contrast,the surface-feedi ng shorebirds haveincreased in every year since 1977-78 (96%in 5 years). Changes for other categorieshave been much less or, in the case ofdabblers and gulls, erratic enough that itis impossible to determine whether the lownumbers of the fifth year are part trendor merely fluctuation. The major sectionsof the lagoon contri buted di fferentl y tothese overall changes in number. Surfacefeedingshorebirds, for example, were ha1 fas abundant in the last 2 years as earlierin the eastern am, increased twofold inthe western arm, and increased fourfoldin the central basin (Figure 40). Cootsdecreased by almost a factor of three inthe western am, but changed little elsewhere.The abundance of gulls has increasedsubstantially in the eastern armand fluctuated in the central basin.A1 though few censuses were conductedbefore the major storm of February 1978,there is no doubt that the filling of mostof the central basin at that time wasresponsible for the increase in surfacefeedingshorebirds there. Since probers,diving and wading fishers, diving ducks,dabblers, and coots were less abundant i~1977-78 than in any of the succeeding 4years, it is possible that a shallowercentral basin has provided more satisfactoryhabitat for them as well, However,this is a suggestion, based on the limitedsampling of the very large Site 21 before

Whole lagoonEast-.JV)GgullsCalF2al DD dlvlnq ducksPall catogor~i*s ofl:sh eat~ng b:rd:,PSCDCentral-;~SObirl~ shoreb~rdssur?act?.feedintj shorcb~rcj.;COO!Sdabbl:ric,! ducks and qeesoFigure 40. Changes In bfrd abundance over time at kgu Lagoon.June 1978, and not a conclusion. Thepartial shift in gulls probably had rnareto do with the extreme eastward migrationof the tldal inlet In 1980 and 1981 thanwlth the filling of much of the centralbasin, since gulls were rnost abundant onthe shifting sand bars or islands associatedwith the inlet. In the western arm,the cmpenratory changes between coots andsurface-feedl ng sharebfrds are cons1 s tentwlth the passfbility that sedimentationmjght favor the tidal flats element, i .e.,surface-feeding shorebirds of the tidalflats-shallw open water couplet,The addftional year of censuses (1976-77) in the eastern ann before February1978 allows more rigorous tests there forstom-ref ated effects, Numbers of probingshorebirds were down In all 13 of thepossible pair-wise compari sans betweenfa1 1 abundances before and after the stamof February 1978 (October - December 1976and 1977 vs. 1938, 1979, 1983, 1981) andwinter through sumrner abundances beforeand after (January - Septmber 1977 vs.1978, 1979, 1980, 1981, 1982). The divingFishers were down in 12 of 13 possiblecmparisons, whereas the dlving ducks increasedin a1 1 13 comparisons. It is un-1 i kely that these outcomes are chanceevents. The former two are consistentwith the known decreases of large invertebratesand fish after the storm.This analysis af Eugu Lasoon birds hasbeen 1 i mi ted to ccdnmon wa ter-relatedspe~ies classified into functionally

elated categories or g~ailds: the birdsthat play important roles in the estuarineecosys tern. Other species are unimportantin the ecosystem because of their extremerarity, but the ecosystem is critical fortheir survival, most notably the liqhtfootedclapper rail (Ra7 lus- longirostris1 evi es) , Be1 ding 3 Savannah sparrowf- Passercul us sandwichensi s be1 di ngi ), andto a lesser extent the brown ~elican(Pel ecanus occidental is) and the' leastf-na a1 bi frons). These endangeredspecies are nmre appropriately discussedin Chapter 7.In addition to the water-related birds,at least 100 species of more terrestrialbirds have been sighted around the lagoon(Macdonal d 1976b; Natural Resources ManagementOffice, U.S. Naval Air Station,Point Mugu, California; unpubl. list).Some commonly use aquatic habitats; forinstance, swal lows often are conspicuouseither pursuing flying insects over waterand marsh or gathering mud from creekbanks for nests. Other species have anaffect on the estuarine ecosystem. Forexample, large birds of prey could beimportant predators on the water-relatedbirds. Nevertheless, the interactionsbetween the more terrestrial birds and theestuarine ecosystem are assumed to be weakand have been ignored.4.5 THE HERPETOFAUNA AND MAMMALSAmphibians and reptiles appear to haveeven less of a role in the Mugu Lagoonestuarine ecosystem than the land birds.Eleven species have been reported (NaturalResources Management Office, U.S. NavalAir Station, Point Mugu, California;unpubl. 1 ist). Observations of westernfence l izards (Scelo orus occidental i s)and side-blotche*~ (U& stansburiana)are limited to adjacent uplands-Conservation Service 1983). SouthernPaci fic rattlesnakes (Crotal us vi ridi she1 leri ) have been encountered in themarsh,1978.particularly after the flooding ofProbably these animals were raftedinto the lagoon on debris washed out ofthe watershed during the February 1978storm.Forty-one species of mammals are recordedfor the Naval Air Station adjacentto Mugu Lagoon (Natural Resources ManagementOffice, U.S. Naval Air Station, PointMugu, California; unpubl. list). Ofthese, four species, the western harvestmouse (Rhei throdontmvs meaalotis -. -.-1 imicola) , kal i fornia s ( ~ i c r o t u ; cal i-fornicus stephens i) , orna te-YXEiT(Sorexornatus sal icornicus) . and black-tmjack rabait (Lepus californicus), areresident in the hiah marsh (Coulombe1970). Hoof prints -bf mule deb (Odocoileushemionus) have been seen along-esandspi t shore of the lagoon (Onuf, pers.observ.), and a variety of terrestrialcarnivores including the coyote (Canis(Vulpes vul es), grayci nereoargenteus 97 , andti s mephitis hol zneri)freauentlv make forays into aauatic habitats.~rbbabl~ the activities'of the terrestrialmammals have minor effects on theMugu Lagoon estuarine ecosystem. Coyotesand red fox den in the high marsh andbeach ridge areas of the marsh. They areactive resident predators and may havesignificant impacts on ground-nesti ngendangered bi rds.The harbor seal (Phoca vi tulina) is conspicuouswithin t h e o o n proper. Over100 seals can be seen hauled out on sandbars near the mouth of the lagoon. Thenumber of harbor seals fluctuates withtides and time of year and averages around40 (R. Dow, pers. comm.). This populationis the only resident seal colony along themainland shore of the Southern CaliforniaBight. Presumably, the isolation of thelocation from human disturbance is cri t-ical for residence by seals. Elsewherealong the mainland, shore sites may beused seasonally as rookeries or for haulingout, but not for year-round residence.4.6 SUMMARYThe spatial and temporal patterns of thebiota of Mugu Lagoon are anything butsimple. The 10 to 20 species dominatingeach major division of the aquatic biota--plants, invertebrates, fishes, and birds--were distributed among several functionalcategories. Most taxa were found in atleast a few physiographic units, butachieved maximal densities in a smallsubset of one unit. The exceptions werethe marsh plants, which were confined to

one physisgraphic unit, but were quitegenerally distributed therein, The microfloralfilms or mats, however, werepresent and important in a1 1 physiographicunits.Elevation appeared to be a minor determinantof distribution for most invertebrates(except that the salt marsh isdistinct frm the rest of the lagoon),since nearby intertidal and subtidal sitesusually resembled each other closely bothin kinds and densities present. Distancefrom the muth of the lagoon had a greatereffect on determining the distributian ofdifferent Functional categories of invertebratesand was perhaps related to hydrodynamiccharacteristics. Only the Cal I-fornia ki1 lifish exploited intertidalflats at high tide; the other fishes weremore canmonly associated wi th the subtidalareas. Canversely, the activities of thebi rds tended to concentrate in intertidalareas: the surface-feeding shorebirdsfeed on exposed flats almost obligately;gulls and most of the aerlal dlverr rooston intertidal sand bars; the problngshorebirds and wading fishers feed nearthe tidal ly migrating waterl ine; and cootsand dabble= feed in the very shallowwater just beyond the tfdal ly migratingwaterl ine. Only the birds that dlve forfish or invertebrates fran the water surfaceand the aerial flshers (when feeding)concentrated their actfvities in deeperopen water areas.Only a few categori es of organisms appearedta be sensillve to sedlment textureand stonn-caused changes in sedf~nent texture.Probf ng shorebirds, large infaunaljnvertebra tes, and eel grass had obvious,strong aff i nlties with predominantly sandyareas, whi5e the opposite was true forsurface-feeding shorebirds, New or previouslyrare tdxa of small infaunat invertebratesbecam very abundant when truemuds first appeared In the eastern arm; atthe saw tfme, the previously daninanttaxa were el imi nated. The blue-greencomponent of the benthic mi crofloraJncreased in response to the same change,A1 though major changer in response tothe storms were evident in many other taxaand categsrJes, changes in elevation ordepth general ty seemed rnore Important thantextura changes. Examples include thelarge decline in the total catch of fishesin the eastern arm, mast evident in speciesassociated with deep areas; the shiftin the distribution of salt marsh plantbiomass; the increase in su rface-feedi ngshorebirds (intertidal) and complementarydecrease of coots (subtidal ). Indirectchanges a1 so were important; for instance,the changes in shiner surfperch partlywere in response to changes frt eelgrass.The decline in the probing shorebirds inthe eastern am almost certainly resultedfran the reductions in the densities oftheir large infaunal prey.The final feature of note is the apparentlyintricate orchestration of the cmingsand goings of migrating blrds andfish, Mugu Lagoon is dominated bybirds in the cold half of the year andfish in the warn half. Domlnant fish speciesor categories of birds with similarfeeding habits vary month by month. It isnot known whether this time-sharing isonly a secondary consequence of some moreimportant aspect of life hfstory or whetherIt Is a consequence of selection forexploiting a Ifmlted resource by a widespectrum of short-term users.The range of environments in Mugu Lagoonis such that only a few species or categoriesout of the small total pool areabundant In any one habftat, but those feware dl fferent between habitats and perhapsbetween times. Even though specles overlapbroadly, they mst overlap in differentportions of their respective toleranceor resource spectra to account for thelarge variety of dfstlngulshable assemblagesof organisms, each cmposed of sucha small number of species,Most of thls descriptjon of the distrlbutionand abundance of the biota of MuguLagoon is based on data cot lected in theeastern am, The description of innerlagoon organ1 sm-habi tat re1 at fans probablyapplfes to large areas of the western armand central basin. Except for the portionof the tidal delta In the central basin,there are no counterparts elsewhere in thelagoon of the sandy environments that areso prominent a part of the eastern arm,The consequences for birds have been described,Fish do not appear ta be stronglyinfluenced by this habitat parameter;however, many of the large invertebrates,

espectal ly the bivalves, are intimately brackish water in the eastern arm. Conassociatedwith the sandy-bottom, subtidal sequently, possibly extensive areas alongchannel, Consequent1 y, large inverte- the Cal leguas Creek channel in the centralbrates probably are much less important in basin and at the western extremity of thethe rest of the lagoon than in the eastern western arm may not be represented in thisarm. There is no persistent fresh or profile.

CHAPTER 5. THE BIOTA:DYNAMICS AMD 1NPERACTlONSMillicent L. QuammnandChristopher P. OnufMany relations of organisms with theirphysical environment inevitably were considzredin Chapter 4 in the discussion ofdistributions. While some of those relationswill be developed in more detailhere, the emphasis will be on haw groupsof oyani sms Interact. The di scusrionwill generally follow the trophic structureof the lagoon.The abundance and rate of chdnge ofabundance of any unlt in the food webrespond to factors at three levels: (1)food availability, (2) intra- and interspec1fic campet1 tion, and (3) predation.Of course, all these reldtjons are modifiedby extrinsic variables such as tmperature,substrate, habitat availabi 1 i ty,dnd storms. A1 though identification ofthe lfnkayes among the jmportant organisrnsof any particular habitat is relativelyeasy, the determination of importance ofthe linkages, and measurement of the ratesof change associated with those linkagesare considerably more difficult.Various researchers have taken threeapproaches to distinguish the effects ofindividual lfnkages or other factors onthe dyrrarnfcs of the Mugu Lagoon estt~arineatcosysten, One rnight be called the blanketapproach: tneasurment of a wide arrayof factors that could conceivably influencethe rate at which a key process proceeds(the independent and dependent vari-ables, respctivelyf . Statistical proceduresare applied to determine how mucheach irrdeperidertt vdrTabf e "'explains" thevardation in the dependent variable. Thesecond method is opportunistic and nmredirect. It capitalizes on extrinsical lycaused major alterations, such as by thestoms of 1978 and 1980, that affect oneor a few factors hut not others, or someareas but not others. This isolates theeffects of one factor or at least narrowsthe consideration to a Pew. The thirdapproach is direct and planned. Manipulationsare speclfical ly designed to a1 teronly one factor while not affecting othersor to a1 tes two or even three Factorsfactorially. The latter allows not onlythe direct assessment of the effects ofthe df fferent factors, but also deternineswhether they interact In any way,5.1 PRIMARY PRODUCTIVITYShaffer and Onuf (1985) and Onuf et al.(1973) compiled preliminary estimates forthe annual productivity of the differentcategories of plants in Mugu Lagoon (Table8). The primary praductivi ty of phytoplankton,benthic m~croflora, and submergedrmcrophytes was de termi ned by di s-solved oxygen techniques (Shaffer 1982).In simul taneous incubations of watersamples and sediments submerged with filteredseawater at the same location, thebenthic microflora were more than twice asproductive as the phytoplankton in thewater colurnn over a similar area of bottm,Submerged i~crophytes were ten timesas productive as benthic microflora.The distributtons and life histories ofthe salt marsh vascular plants at MuguLagoon were such that net changes over agrowing season simply could not express

Table 8. Primary productivity in Mugu Lagoon: estimates of annual productivity fordifferent sources, the conditions to which the estimates apply, and conversions tosimilar units. GPP = gross primary productivity, NPP = net primary productivity, NAPP= net aerial primary productivity.SourceEstimate ofprimaryproductivityas measuredNP!(g C m- y-'1Factor tounderconvert-io conditionsAppl ies to g C m-' y NPP measuredPhytoplankton%70 g C m-2 y-' GPPa Subtidal NPP = 0.77 GPP~areasBenthicmicroflora 170 g C m-' y-' GpPa Intertidal NPP = 0.77 GPP~ 130flats whenflooded +subtidalareasSubmergedmacrophytes $1,700 g C m-* GPP~ 2.10% of NPP = 0.77 GPPa 1,300intertidalflats whenflooded +2.10% ofsubtidala reasSalt marsh290 g dry wt m-* y-l NAPP~ Low marsh g C = 0.25 g dry wtC 70macrophytes 730 g dry wt m-' y-l NAPP~ High marsh g C = 0.25 g dry wtC 180much of the production. Therefore,monthly measurements were made on 50 - 300tagged shoots of each of four species asthe most direct measure of growth, turnover,and production (Onuf et al. 1979;Onuf, unpubl. MS!. To give an idea howimportant the turnover component of productionis, more shoots of Salicorniavirginica died during the period of increasein the green parts of plants fromJanuary to August than the maximum numberof shoots that were alive at any one time(Figure 41). Over the whole year thistranslated into a production of 2.3 timesas much biomass as could be identified bynet increase. The result was similar forthe three other species to which themethod applied. Production estimated fromtagging was 3.7, 1.8, and 2.9 times thenet change over the growing season forJaumea carnosa, Limonium cal ifornicum, andBatis maritima, respectively (Onuf et ale1979).Only the most general comparisons arewarranted among the productivity estimatesfor the different kinds of plants (Table8) because of the difficulties involved inconverting the various estimates into the

5000accumulated deadfI5 hours. High in the intertidal zone (theupper parts of the salt marsh), where exposurecan last for days, productivity ofexposed microalgae is bound to be muchsmaller than productivity of submergedmi croal gae .oJL ' M ~ RCI_LL-__L-".I-__LL-.J' MAY JuL sEP Nov JANFigure 41. Density of shoots of x-cornia vir inica in the lower marsh of~ L a h v at e different timesduring the growing season and accumulateddead since January.same units and applying estimates to conditionsother than those under which themeasurements were made. For instance, themeasurements of submerged macrophytes andbenthic microfloral productlvi ty were madeunder submerged conditions, yet bothgroups of plants occur intertidally aswell as subtidally and are exposed to theair at least some of the time. Productivity probably is d'ifferent in air than inwater, especially at higher elevationswhere the sediment surface can dry completely,but we don't know how different.Using high marsh sediment collected atMugu Lagoon, Holmes and Mahall (1982)measured gaseous GO2 exchange from initfally flooded sediments as the sedimentsdrfed fn an airstream. Photosyntheticrates of the benthic microflora increased,coinciding with the disappearance of avisible water film on the sediment surface,and remained higher than the submergedrate for 1 and 4 hours in twotrials, Respi ration exceeded photosynthesisafter 3 and 6 hours of desiccation,at which times the water contents of thesediments were 85% and 75% of saturation,respectively, These results qua1 i tativelysuggest that exposed and submerged productivitymay not differ greatly low in theintertidal zone (the sand and mud flats)whew daytime exposure seldom exceedsThe main caveat about the productivityestimates for the salt marsh vascularplants is the uncertainty arising frommeasurement techniques and calculations.The monthly estimates are imprecisebecause of the high spatial heterogeneityof the marsh. These errors arepropagated in the mathematical manipulationsused to generate the annual estimates.Bearing in mind tbese essential qualificationsabout comparisons between kindsof plants, extrapol ations to conditionsnot sampled, and shortcomings inherentin the techniques themselves, the contributionsof various sources to theannual production of the eastern armof Mugu Lagoon are indicated in Figure42. A1 though the submerged macrophytes(mainly the green algae Enteromorpha andUlva) are the most productive plants-where present (Table 8), they cover arelatively small area in the lagoon onaverage over the year and make a relativelysmall contribution to the primaryproduction of the entire system. Theemergent vascular plants of the saltmarsh and the benthic microflora of theflats and subtidal areas are, in comparison,only moderately productive; but byvirtue of the large areas that they occupy,they heavily dominate total production.Shaffer and Onuf (1983) sought to explainvariation in benthic microfl oralproductivity by relating every determinationof productivity to correspondingmeasurements of chlorophyll 2, solarradiation, water temperature, communityrespiration, sediment composition, andinitial dissolved oxygen for each sample.The multiple regression performed on theentire data set accounted for only 38% ofthe observed variation. When the multipleregression analysis was redone monthby mnth and for sites grouped accordingto similar substrate history (similarresponses to the major storm that occurredhalf way through the study; see

.-0)Subtidai 21% of areaIntertidal flats 11% of areaLow marsh 25% of areaHigh marsh 44% of areaEntire eastern arm5.2 THE AVAlLABlLfPY OF PRIMARYPRODUCTION TO CONSUMERSMost of the plant material produced inMugu Lagoon is separated spatially andtenporal ly from most of the potential consumers,since most production is in thesalt marsh and most consumers occur subtidallyor in the intertidal flats, Thebiomass of some of the sources is tootough for most primary consumers of theecosystem,+increasingly so fran the macroalgaeEnteromor ha anh through thesubmerge vascu ar plants Zostera andRuppia to the emergent v a s c u l ~ t of sthe salt marsh. esoeciallv those withwoody parts such- as ~ aicorhia l virginica,The nutritional quality of some of thesources is low for most consumers. Inmany cases this is strongly correlatedwith toughness. The high proportions ofstructural carbohydrates (e.g., lignin,cellulose) that make for toughness inplants require that too much bianass mustbe processed to obtain other necessarymaterial s for maintenance, growth, andreproduction. For many aquatic consumers,amino acids are in critically short supplyin these sources of primary production(Russel 1-Hunter 1970). A1 so, animal s maylack the necessary enzymes for digestion,or palatability may be low." Phyto- Benthic Sub- Emergentplankton micro- merged rnacrofloramacro- phytesphytes0Estimates based on few measurements orextrapolated from other conditionsEstimates based on many measurements underindicated conditionsFigure 42. Contributions of differentsources to the total net primary productivityof the eastern arm of Mugu Lagoon.Figures 15, 16), the variance explainedwas much higher (60% of the average)than for the whole data set. In themonthly categorization, each of the sixindependent variables was most importantduring at least lmonth. Thus, theintuitively important factors were moreimportant than the pooled analysis indicated,but not in the same way at alllocations or at all times.There is almost no direct consumption(eating of live or recently dead plants)of the vascular plants of the salt marsh.The exceptions are (1) rare infestationsby an unidentified scale insect and anunidentified moth larva on Salicorniavir inica (Onuf, unpubl. o b s e mdb- ee inq - bv - Be1 dins's Savannah s~arrows onthe succulent tips of ~alicornia andSuaeda plants when insects are rare-Y 19791, and (3) uarasitization bydodder (cuscuta sal'ina), presumably asmuch an h m e as S~D-suckins scaleinsect. Thus, the primary ' consumption ofmost of this material is only after ttsdeath along a detrital pathway. Althoughmacroinvertebrates often play a major rolein the breakdown of this material, thereis little or no indication that they directlyassimilate the organic material o#the plant. Rather, they assimilate theorganic matter of the microbial decmposerson the surfaces of the detritus(Adams and Angelovic 1970). Perhaps thestrongest evidence that the activities of

the micrabi a1 decomposers de teni ne thenutritional value of detritus for detsitivorescmes from Tenore's (1980) grswthexperiments on the deposi t-feedfng polychaeteCap1 tel la capi tata, provided dietsof detr~ tus of different ages and fromdifferent sources, Growth was much morestrongly correlated with microbial respirationthan age or source,The consequence of this intermediatestep in plant utilization by macroinvertebratesis a decreased efficiency oftransfer of carbon or energy from primaryproducers to the upper levels of thelagoon's trophic web. It also increasesthe time required to complete the transferfrm prlmary producer to macrofauna. Thisincreases the chance that something elsemight happen to that organic material producedwithin the system before utilizationoccurs within the system. The most likelyalternative fates are export From theestuarine ecosystem to coastal waters byebb tides or export in the opposite directionto the upland transftion zone bysprjng high tides, especially when accornpartiedby strong winds, surf, or stormflows that can raise the stand of thewater In the lagoon far above the normaltidal extreme. In this case, the productivityof the niarsh is utillred mostly byterrestrial consumers, The physfcalseparatfon of the potential subtidal estuarfneconsumers from the salt marsh sourcei ncreaser the li kel i hood that an@ of thesealternatfve paths may be followed, apeciallywhen it is considered that rmst ofthe consunrers are in or on the bottan,while mrch of the material in transit cnaybF3 floatlng on the water surface.The characteristics of phytoplankton andthe benthic microflora that define theirtrophic relations are alimst di&netrlcal lyapposed to those just described for thevascular plants of the salt marsh (Table91, These microbial plants are jntlmatelyassocf at& wi tR numerous consumers and arereadf ly ingested and presumably assimilatedl.However, they probably leak theircontents faster in life and after deaththan the salt marsh mcrophytes, and thisdecreases their availability to macroconsumers.Also, they decrease in nutritfonatquality very rapidly after death,while the salt marsh macrophytes slowlyincrease, kspi te these restrictions,the net result is that the trophic efficiency(proportion of the h-iornass OF theplant converted into mitcrofauna! bj0iniissjwithin the estuarine ecosysterti;l is ruchhigher for phytoplankton and benthicmicroflora, and mrlch less is exported tosome other systm than for salt 1~3ar;hmacrophytes.The differences in the availability ofbenthic microflora and phytoplankton toconsumers are a consequence of mode ofpresentation (adhering to a surfacc vs,suspended in water). These tli fferencesprobably affect the kind of conrumer (depositfeeder vc,. suspension feeder) inorethan the amount that is available for consumption,a1 though the gelatinous sheathon some f i ldrnentous cnlonial epiphyticfornis of benthic microflora light be anobstacle to herbivores as it can be inmany freshwater systermrs (Porter 1977).Also, the difference in surface to volumeratios between planktonic and benthicoccurrence shou'i d affect leaching rates.Plnally, when benthic mats lift off thebottotn en masse and float on the surfaccof the water, hayed up by oxygen bubblesduring perfods aF active photarynthesis(see Chapter 41, they are more lfkely tobe stranded in the high-tide wrack thanrnateridl suspended in the water col urnn,Nevertheless, phytoplankton and the henthicrnicroflora are trophical ly very simllarin thfs system.The submerged rnacrophytes are intennediatein their trophic characteristicsbetween the extremes posed by salt marshvascular plants and the rrlicroflora. Submergedtnacrophytes and the bulk of themacrofaunal primary consumers of theestuarine ecosy%tm are in close proxiniity. The subrrrerged macrophytes are notimtwdiately accessible to the infauna, butare only centimeters away and actuallyserve as the substrate for sane surfacedwellingfarms. They [nay be out of reachor too refractory for sane or most consumerswhen alive but rapidly becorw nioreavailable after death (at least judging bytheir rapid rates of loss compared tomarsh plants [Figure 431). As a result ofthese characteri stics, submerged rtlacrophytes;re likely to De tis& wit9 ;wderatetraphic efficiency wl thin the estuarineecosystetn, and trmderate quantities wi 11 be

Tabie 9. Factors reducing the util ization of d source of primary production by macroconsumerswithin the Mugu Lagoon estuarine ecosystem,FactorBenthicmicrof loraP hy to- (including Submerged Salt marshpiankton epiphytes) macrophytes macrophytesPhysical or temporal None None Small Largeseparation betweensource & consumerLive ti ssue unmanageabl emechanicallyNoSt ightly Moderately Ve ryLive tissue low in nutri- N o No Moderately Verytional qua1 i tyAging requi red before N o No Brief Longconsumpti on as detritusExport to coastal waters Moderate Moderate High HighExport to upland edge No Slight Slight ModerateLeaching of di ssol ved or- High Moderate Moderate Lowganic matter from 1 ivingto lowplantsLeaching of di ssol ved or- Very high Very high Moderate Moderateganic matter from deadplant materialexported to adjacent terrestrial andmarine systems.There is one possible qualification inthis analysis of the trophic status of thesubmerged macrophytes. The very highlevels of production that are possiblelocally and rapid decomposition can be toomuch of a good thing. The mats of decomposingseagrass or macro1 agae can becomeso thick that the lower layers go completelydnaerobic, turning the surfacelayers of the sediment into a black,hydrogen-sul fide-produci ng flocculentlayer. A1 though some benthic invertebratescrawl into the overlying a1 gae, theinore sedentary organisms are probablykil led (Onuf and Shaffer, pers. observ.) .Clearly this will decrease trophic efficiency.In summary, the characteristics and distributionof the phytoplankton and benthicmicroflora make them immediately availableto a wide variety of macroconsumers. Mostconsumption of these plants probablyoccurs while they are still alive. Relativelylittle of the organic matter producedis exported beyond the productionsite. Therefore, phytoplankton and benthicmicroflora are probably used withhigh trophic efficiency within the estuarineecosystem.Submerged macrophytes are immediatelyavailable to some consumers but localproductivity can be too great to be entirelyconsumed. Some, perhaps most,submerged macrophytes are consumed asdetritus, soon after death. Some

the lagoonal fauna, Consklering the re1 a-tively high availability of benthic microfloraand very low availability of saltmarsh vascular plants, it is likely thatthe benthic microflora is the most importantfood for primary consumers in thelagoon, fol lowed by submerged macrophytes,salt marsh vascular plants, and phytoplankton.In contrast, salt marsh vascularplants contributed most of the totalestuarine primary production, fol lowed bybenthic microflora, submerged macrophytes ,and phytoplankton (Figure 42).5.3 PRIMARY CONSUMPTION00 100 200DaysFigure 43. Decomposition in water ofmacrophytes that occur in southern Californiacoastal wetlands (adapted fromNixon 1982 with values for ?partinafol i osa and Sal i cornia bigel ovi i fromWJnfl'eld 1980).submerged macrophyte biomass is exportedout of the estuarine ecosystem.The salt marsh macrophytes are unavailableto most consumers until considerableaging as detritus has occurred. Much oftheir biomass probably is exported tocoastal waters and to the terrestrial edgeof the estuary. Consequently, salt marshmacrophyte biomass is used with lowtrophic efficiency within the estuary,The preceding is a conceptual analysis,supported only by qua1 i tative observationsin Mugu Lagoon. Nevertheless,differences in the availability of themajor primary producers to macrofaunalcowimers will have major consequences forthe trophodynamics of the Mugu Lagoon estuarineecosystem, No quantitative estimateof the effect of differential plantavailability on trophodyna~nics is possible;however, the di fferences in avail -ability seem so large that primary prodnctionby itself is a poor indicator of theimportance of a plant type in support ofTypically, a food web is composed ofseveral distinct groups of organisms atany trophic level. A major determinant ofthe structure of the next higher level isthe separation among consumer groups accordingto which of the available foodresources they exploit. The primary consumersof the Mugu Lagoon estuarine ecosystemare differentiated according tofood source only to a limited extent. Forinstance, in the salt marsh, the snailMelam us 01 ivaceus usually is associatediiETi%kense accumulations of Limoniumcalifornicum leaf litter, and judging-bythe feeding preferences of its similarlylocated congener M. bidentatus in Atlanticcoast salt mars-jies, it feeds on thatlitter (Rietsma et al. 2982). On theother hand, Ceri thidea cal ifornica, theother common snail in the marsh, grazesthe sediment surfaces and the stems of themarsh plants. Although it also consumesfragments of the marsh plants, benthicmicroflora is its main nutritional source(Whi tl ach and Obrebski 1980). Final ly,the crab Pach ra sus crassipes scrapesthe sediment -=-!5h surface en it feeds in themarsh (Onuf and Quammen, pers. observ.).Certainly it ingests the benthic microfloraon the surface, but the detritus andorganisms in the sediment immediatelybelow the surface are likely to be muchmore heavily exploited than by Ceri thidea.In other parts of the ecosystem, nicheseparation according to source of primaryproduction is less evident. The onlyobligate grazers on the submerged macrophytesare the California brown sea hare(Aplysia cal i fornica) and brant, and theyare found only occasionally within the

lagoon. Coots and dabbling ducks feedupon submerged macrophytes, brat also takesmall invertebrates in the sediment. Thecrab Hemigrapsus oregonensi s certainly iscapable of shredding 1 ive macrophytes andwill grow well in the laborator~y providedsolely with Enteromorpha (Kvris and Mager1975); however, in nature it feeds on diatm~sas we1 l (Morris et a7. 1980) and is ascavenger and a predator (Chapman et al,1982). As for the rest of the primaryconsumers, they depend mostly on the samefood: small organic particles, probablywith little discrimination as to origin,whether they are true phytoplankton,benthic microfl ora, fragments of submergedmacrophytes, or detritus derived form sal tmarsh vascular plants, Also, a widevariety of organisms are, to a limitedextent, capable of upta1.e of dissolvedorganic carbon (Stephens 1.982). Bacteriaand other microbial decotnposers are importantnutritional sources and are consumedmainly in association with detritalparticles.Apparently, loca tional factors and thephysical characteristics of habitats aremuch more important than plant type inexplaining the relatively great variety ofprimary consumers in the Mugu Lagoon estuarineecosystem. Thus, very differentorgani srns will use the same fine-particledorganic material, and they will do so invery different ways depending on whether:(1) it is suspended in the water column,adhering tu surfaces, or mixed in sediments;(2) the sediment is sandy or muddy;(3) the location is never exposed to airor seldan flooded; (4) water movements arefast or slow; or other factors.The bivalve mollusks and ghost shrimpprovide the best illustration of how theprimary consumers of Mugu Lagoon arepartitioned in the apparent absence ofdifferent food sources. Peterson (19771,following Warme's (1971) analysis, describedthree distinct assemblages in theeastern arm according to the substratetype with which they were associated, Thesand community (95%-98% sand, i.e., particles50.06 mm) occurred in the subtidalchannel, which connects the subtidal pondsof the eastern arm to the mouth of thelagoon (Figure 13). The "mud" cmmuni ty(actually 50%-90% sand) occurred in thewestern subtidal pond, and the muddy-sandcmmuni ty occupied a narrow trans1 tionafzone between the other two communities,extending especial ly a1 ang the south shoreof the subtidal pond beyond the entry ofthe subtidal channel (Figure 13).The three communities were characterizedby very high volumes of rnacroinvertebrates,dominance by five or six species,dominance of suspens ion-feedi ng, andstrong stratification among species accordingto their depth in the sediments(Figure 44). Ordinarily, several speciesexploiting the environment in the same waywould not be expected to coexist in thesame place (Gause' s cmpeti tive exclusionprinciple). There are three general explanationsfor how similar organisms cancoexist. Their densities can be heldbelow the level at which competitive exclusionsoccur by: (If physical disturbance(temporary extreme condi tions thatcause mortality), or (2) losses to naturalenemies (predators, parasites, or pathogens),or (3) resource partitioning (nichedifferentiation).The very high volumes of organisms(6,000 to 8,200 cm3 of organisms/m2 ofbottom) that are continually present suggestthat populations are at or nearcarrying capacity , thus el iminating explanations(1) and (2). However, tests sofar have failed to demonstrate the necessaryselective feeding among fi 1 terfeedingbivalves (Vahl 1973) to make partitioning of the food resource a possibility. These considerations, together withthe clear evidence of depth stratification,led Peterson (1977) to infer thatcompetition was the main factor responsiblefor the organization of all three canmunities, but that space, rather thanfood, was the resource in short supply.According to this interpretation, organismsshould be much mare sensitive tochanges in the densities of organisms inthe same depth than to changes in thedensities of organisms in other strata.Several independent 1 i nes of evidencebear on this hypothesis. The ghost shrimp,Call ianassa cal i forniensis, over1 apsbroadly in depth in the sand communitywith the clam' Nuttallia (San uinolaria)nuttall i i ( F i g u r m o w e b -vidual samples, where one is abundant, theother tends to be rare, Thus, whereas

a SAND MUDDY SAND e "- Protothaca Protothaca-MUD'IFigure 44. Stratification in the depth of living position of the abundant shelledinvertebrates in sand, muddy-sand, and "mud" habitats of Mugu Lagoon, based on hand-dugsamples (adapted from Peterson 1977).niche overlap is broad in the horizontalplane for many inhabitants of the community and narrow in the vertical dimension,the opposite is true for Call ianassa andNuttallia. After Peterson (1977) eliminatedmCallianassa from part of an areawhere they had been abundant, juvenileNuttallia were 60 times more abundant thanwhere Callianassa had not been removed.Apparently, Call ianassa 's intense reworkingof the sediment (all the sand to adepth of 50 cm in a few months, accordingto MacGini tie's [I9341 calculation) ki 1 lednewly settled Nuttallfa by burial or perhapsingestion. Alternatively, Nuttallialarvae may have selectively settled in theremoval area, respondi rig to physicochecnicalchanges in the sediments, such as increasedanoxi a.The mechanism that seems to determineNuttallia's abundance and size in themuddy-sand community is almost the exactantithesis of that just described for thesand community. Here, its depth range isoccupied by two very large clams, Tresusnuttal li i and Saxidomus nuttall i i , threeto four times as large as Nuttallia, withlarge siphons extending to the surface.When Nuttallia were introduced to themuddy-sand community in the presence ofdifferent species of the natural communityand in isolation, their growth was unaffectedby the surface dwellers (the clamProtothaca staminea and the sand dollarDendraster excentricus). But growth wasdepressed -80% by the presence of theoccupants of their preferred depth stratum(Tresur and Saxidomus) (Peterson and Andre

1980). Also, there was an increased tendencyfor Nuttallia to emigrate in thepresence of Tresus and Saxidomus.In an additional experimental treatment,in which live Tresus and Saxidomus werereplaced by she1 1s filled with sand andfitted out with surrogate siphons madeout of wood, the growth of Nuttalliaalso was reduced significantly. In contrast,surface-dwell ing Protothaca werenot affected by the Presence of eitherNuttallia or ~resus and Saxidomus, eventhouah all four s~ecies are sus~ensionfeed

sand where they occurred* 3udging fratthe low sediment carbon values in Warme's(1966, 1971) analyses for the sand channel,filter feeding may be necessary atMugu Lagoon as we7 1.The blol ogy of other primary consumersin Mugu Lagoon is not well studied, Thefour small crustaceans that have beenabundant at least sporadically in theeastern arm between 1977 and 1982 areassociated with compacted sediments andhard surfaces (the gamma ridean anphi podGorophium acherus icum), the surfaces ofmacrophytes (another gammaridean amphi pod,and unconsol idatedcaprel lid amphSpodand the cumacean. They eitherss loose particleson a surface or suspension feed (J.W.Chapman, EPA, Newport, Oregon; pers.cmm.). Only Pontogeneia is likely toexploit other f~snurces in add1 tion tothe small particf e mix of benthic microfloraand detritus, Encrusting animals aswell as macroalgae are prminent Anhabitantson the surfaces of rnacraphytes andmay be eaten by . Thus, locatlonnlfactors amore importantthan diet in niche differentdatlon for thesmall crustaceans as well as for thebl val ves and yhos t shrimp.No one has studded the feeding habits ofthe soft-bodied invertebrates at MuguLagoon in detail ; however, general iza tionsmay be made based on studies elsewhere onthe same or related species.There are three modes of primary consumptfon among the saf t-bodied ?nvertebrakesaF Mugu Laqoon: suspensionfeebfng, surface-deposi t feeding, andsubsurface-deposl t feeding dl1 e hrrowing,A17 are based on fine particulateorganic matter. As with the clams andCall Sanasza, the distinctions among feedingmdes are blurred, For Instance, in astudy of feeding in three species ofspionid warns nomally classified assurface-deposit feeders, Taghon et al.(1388) denrons t~ated changes between deposft feeding and suspension feeding, dependingon the flux of particles grassingby in the water column, Alternatively,Jumarr, et a1. ((182) reported an abruptswitch to "a decidedly macrophagous, predatorymode" when small crustaceans warminto the tentacles of two os thesespecies, These Findings almost certainlyare of significance in Mugu Lagoon, Halfof the '"mall worm-like" taxa listed inTable 4 are spionids. Furthenore, theanimals used in the studies citrd above,collected on San Juan Island, Masklington,were in the sarile shallow-watev, softbottomenvi romnent as in Mugu Lagoon.As with the other major grouos of primaryconsumers, spatial separation ofsof t-bodied invertebrates ir co~spicuaus,Depth stratification is iinplici t in thenarnes of trophic groups that exhibit suspensionfeeding, surf ace-deposi t feeding,or subsurface-deposi t feeding (above, on,and atnder the sediment surface). In aifdltion,Whi tlach (1980) documented verticalstratifjcdtion within the sediments in hisstudy of the deposit feedlng conrirluni tiesof Barnstable Harbor, Massachusetts, aswell as horizontal differentiation, Inparticular, he observed that many morespecies co-occurred in samples rich inorganic matter than in sarnples that werepoor in organic matter. Furthernore,those that were abundant across the wholerange of sediments sampled overlappedless with other species in depth distributionand particle size utilization t.hanthose that occurred only where organicmatter was abundant. Whi tlach (1980)inferred frm these patterns that cmpctitive interactions were important determinantsof the organization of the depositfeedingguild. When food was meager, onlythose few species that were distinctlydl fferent in their feeding characteristics,especial Iy feeding location, couldco-occur. When the organic content of thesediments was high and presumably food wasabundant, these species were joined byothers that over1 apped broadly wi th eachother and with those already present inboth the1 r vertical distributions andparticle-size utilizations. Densitydependentpredation, interference amongconspecifics at high densities, or sotneother factor may have to limit the specialistswhen food is abundant, Otherwise, why don' t the speci a1 i sts increaseta the point that food again is too irreagerfor generalists, regardless of the rate ofsupply?

Despite uncertainties about the precisemechanism of interaction amng the softbodiedinvertebrates, biof ogical interactionsare major determinants of the organizationof this group. Spatial differentiationis one manifestation of thoseinteractions. Although the analysis offactors invof ving the relations among thesof t-bodi ed invertebrate primary consumersrelies on information collected in othergeographic regions, concl usions aresimilar to those from the detailed studiesof the shelled invertebrates at MuguLagoon, Namely, a high level of spatialsegregation al1ow.s a varied assemblage ofconsumers to subsist on essentially thesame food resource,5.4 PREDATIONIn Mugu Lagoon, secondary consumers areconfronted with a wider choice of possiblefoods than the primary consumers. Ofcourse, the secondary consumers are confrontedwith the same challenges posed bythe physical environment as are the primaryconsumers. Secondary consumers canexploit their food resource selectively bykeying in on a specific prey (for instance,ambush predation by halibut oncrustaceans or other fish) as well as bykeying in on a specific physical environment(for example, shallow-feeding shorebirdsfeeding on a mudflat).Birds and fish, the two most obviouscategories of secondary consumers and probablythe most important, are constrainedfirst by characteristics of the physicalenvi ronment. Shorebi rds are 1 imi ted tointertidal areas and can use them onlywhen they are exposed at low tide. It isequally obvious that fish and diving ducksare limited to areas covered by water.Although this does not preclude their useof intertidal areas, it reduces the availabilityof those areas compared to areasthat are always submerged. As describedin the previous chapter, there was nodiscernible difference in the speciescmposi tion or abundances of invertebratesbetween intertidal and subtidal benthicsamples in the same general area of thelagoon. This suggests that, at least atthe grossest level, differentiation of thephysical envi ronment is more importantthan differentiation of the food supplyIn determining the organization of thesecondary-consumr trophic I eve1 . (Thisanalysis may not apply to the small crustaceans,because they were not adequatelysampled by the techniques used.)The most conspicuous predatory activityin the Mugu Lagoon estuarine ecosystem isthe scurrying about of shorebirds on themudflats, sticking their bills into themud every few seconds and presumablypulling out something to eat much of thetime. Since small worm-1 i ke invertebratesare usually the abundant organisms nearthe surface of the mud, it is reasonableto infer that they are the principal preyof the shorebirds. Given the abundance ofthe shorebirds, it is likely that theyconsume many worms; however, that is asfar as reasonable inferences can go. Itcannot be said whether predation substan-tially reduces the densities of worms,a1 ters the relative abundances of differentspecies or, if either of these occurs,whether the shorebirds are responsible forthe effect (rather than fish that can forageon the mudflats at high tide).A number of field experiments at MuguLagoon and Upper Newport Bay, Cali fornia,have elucidated the predator-prey re1 a-tionships between shorebirds and softbodiedbenthic invertebrates (Quammen1981, 1982, 1984). At a muddy (8% sand)site studied by Quammen, benthic invertebrateswere much more abundant in summerthan in winter (Figure 45a), when surfacefeedingshorebirds were abundant (Figure45b), and their feeding activity wasintense. At a muddy-sand (80% sand) site,densities of the same invertebrate specieswere higher in summer than in winter (Ffgure45a). The differences in seasonalabundance were explained by both predationand site characteristics. When shorebirdswere experimentally excluded at the muddysite, infaunal densities remained highthroughout the year, clearly pointing topredation as a major factor in controllinginfaunal abundances. Quammen found, however,that the addition of a thin layer ofsand to muddy sediments reduced shorebirdfeeding activities by more than ha1 f, Theadded sand did not after the mud surfacevisually, nor the density of the worms inthe top 2 cm of sediment, suggesting thatcoarse particles at densities higher than8% in surface layers of mudflats deter

the crabs were not present, densitiesinside and outside the exclosures weresimilar. Thus, crabs, not shorebirds,were the major predators on the invertebratesin the muddy-sand sediments, However,even here, shorebirds (in this case,the large probing shorebirds rather thanthe small surface-feeding shorebirds) maybe ultimately responsible for the seasonalpattern of abundance in infaunal invertebrates.Large shorebirds, especial lywillets, preyed heavily on the crabs whenboth were present on these flats for abrief overlapping period in the latesummer (Figure 45c). Thus, the absence ofcrabs, perhaps in response to the relativelyhigh densities of willets, togetherwith the low abundance of surface-feedingshorebirds, accounted for the high winterpopulations of the soft-bodied invertebratesin "sandy" mudfl ats.MonthFigure 45. The abundances of worms,surface-feeding shorebi rds, and crabs andwillets through the course of a year attwo locations varying in sand content ofthe substrate. Crabs were not present atthe muddier site.shorebird feeding, probably by interfering~4th prey capture.Predation control led the infaunal abundanceat the muddy-sand site, but in adifferent manner. Use of the site bysurface-feeding shorebirds was much lowerthan at the muddy site (Figure 45b), perhapsin part due to the interference ofcoarse-grained sediments described above.Another predator, the lined shore crab( crassi es) was abundant duriiT-#k- e site (Figure 45c),but was absent at the mddy locations.When the crab was abundant, infaunaldensities were low. When crabs wereexcluded, densities of the benthic inver-tebrates increased re1 a Live to those outsidethe exclosures, In the winter, whenIn sumrnary, predation, especially byshorebirds, is a major influence on thesmall sof t-bodied primary consumersinhabiting mudflats. The influence is astrong seasonal effect on abundance becauseof the migratory habit of shorebirds.Predation may produce oppositepatterns of seasonal abundance on intertidalflats, depending on the amount ofsand in the substrate and whether theshorebirds prey directly on the worms ofthe mudfl a ts (su rface-feedi ng shorebirdswhere little sand is present) or on thecrabs that prey directly on the worms.A1 though not explicitly stated above,another important characteristic of theseinteractions is that there is no obviouseffect on the relative abundances of preytaxa; i.e., apparently there is littleselection among prey or differentialresponse such as might be expected forprey with different life histories subjectedto the same intensity of predation.Changes in the relative abundances of differenttaxa are more common in other systems.Physical factors seem to be muchmore important in defining the characteristicsof the trophic interaction thanwhat prey are eaten.Peterson's (1982) exhaustive study ofthe population biology of the similar andre1 ated bivalves Protothaca staminea andChione undatella provides a strong contrastto the preeminence of physical factorsover characteristics of the prey in

determining the features of the 1 i nkagebetween primary and secondary consumerlevels, Here, despite similar position inthe substrate, shape, and to a lesserextent size, Protothaca suffered re1 a-tively high mortality, mostly attributableto a variety of predators, In contrast,mortality in Chione generally was low, and1 iitle or no mortality was caused by predation.Apparently, Chione's sf ightiybigger size and heavier she71 at all sizesmade it essentially immune to predation.In complement to these survivorship patterns,recruitment by Protothaca was overan order of rnagni tude higher and less variablefroin year to year than recruitmentby Chione.For the most part, fishes in Mugu Lagoonare not major consumers of infauna. Apartial exception is sipt ~n-nipping (partialin the sense that the victim survives,unlike the victim in most predatorpreyinteractions). For Protothaca, theeffect of siphon-nipping can be considerable,depending on location.Peterson and Quammen (1982) observedthat the growth of Protothaca in the cleansand environment at Mugu Lagoon was overtwice as great inside cages that excludedlarge predators (6-mm openings) as in cagecontrols or open areas, but that there wasno difference in the muddy sand environment.This suggested that the presence ofpredators affected growth in one area butnot the other. Observations of Protothacafn aquaria eliminated the possibility thatreduced growth was the consequence ofclosing up for protection in the presenceof potential predators. Protothaca fedjust as actively in the presence of a varietyof predators as in their absence.Clam siphons were common in the guts oftwo fishes, the staghorn sculpin (Leptocottusarmatus) and the diamond turbot(Hypsopsettaguttul ata). Reducedqrowth would be an expected cost of reqen-Grating the siphon. Also, feeding effjciencyis likely to be lower until the feedingorgan is fully replaced. Therefore,the cropping of siphons by fishes probablyaccounts for the enhanced growth of Protothacawithin exclosures in the clean sandenvi ronrnent.The interesting thing is that there isno such reduction in growth in the muddy-sand envi ronment, despite higher densities(2,3x) of the two important croppers andsiphons occurring more frequently (1.8~)in their diets. The explanation issimple. Not only was Protothaca muchdenser in the muddy sand site than in thecl ean-sand site (2,7x), but a1 so anotherbivalve, Macoma nasuta, was even denserthan ~rotothaca 'm-. The net resultwas that Macoma bore the brunt of thecroppins [ T i n this environment asdeternined'by identification of siphons inguts to species, The remainder was distributedover a bigger population of Protothaca,such that the cropping rate perm u a l was at least 40% lower than inthe clean sand. Thus, in this case, thepresence of an alternate prey accounts fora difference between locations in the outcomeof a trophic interaction.We know the other feeding activities offishes froin analyses of their gut contents(Table lo), but the effects on lower trophiclevels have not been worked out insuch detail as the cases described above.Some species concentrate on a narrow rangeof food. Large California halibut, forinstance, feed mainly on other fishes,while large topsmel t contain (feed on?)plant material and mud (or the diatom filmassociated with it?), and large shinersurfperch eat mainly small crustaceans(gammarid and capre11 id amphipods, andcumaceans). However, the diets of theselatter two species change ontogenetically.The smaller sizes of both species eat zooplanktonalmost excl usively. The otherspecies listed in Table 10 have more varieddiets, For instance, small crustaceansand gastropods were most importantfor California kil lifish, whereas polychaetes, moll usk siphons and large crustaceanswere most important for diamondturbot.Despite the variety of foods consumed bythe fishes of Mugu Lagoon, two commontrends are evident. First, the feedingactivities of the fish tend to be focusedat sediment or submerged plant surfaces orin the water column rather than in thesediment. Only the sixth most abundantfish, the diamond turbot, commonly con-sumed buried prey (po'lychaetes), and eventhen other items were at least as important.In this characteristic, the ffshare almost rfian~etricaliy the opposite of

Table 10. The gut contents of fishes in Mugu Lagoon, February 1977-January 1478,all stations (see f'igure 34) and rllonths comblnd. See fable 4 for the taxonortriccmpas'llion af mst prey categories. 0 = overwhelming predo~inance, k( = veryimportant, I = Important, G -. cwfilrrron, P = present.Food typesI-.E t a ,-3 m u arV) ck i w 5 2 C,D 6 u m u ICrRT w Co w 4.- UL 0.r- .,-Shiner ourf~~rch4 100 mn 133Cal Ifornf d ha1 ibutclQO mnr 3 1. P CdPan togeneia1-1 ":kGta~~ shrimpm GobyoFish mbryosFish fry, ernbryos, and pipefish,

the shorebirds, the other irnportantsecondary consumers of Mugu Lagoon, sincethe shorebirds consume polychaetes andother invertebrates living Sn the sedimentsto a greater extent than speciesthat 1 ive on the surface or in the watercolumn. Thus, the two groups of secondaryconsumers are complementary in what theyfeed on as we1 1 as where and when (seasonallyand during a tidal cycle) theyfeed,The other trend is the prevalence ofcrustaceans in the diets of the fishes.This is especially true of the small crustaceans,important at some stage of lifeto a1 1 fish species except the topsmel t.The converse does riot appear to be true,however: important as ssral 1 crustaceansmay be to fish, fish do nct appear to havemuch effect on the popuiations of smallcrustaceans, This is the tentative interpretation of the fol I owi ng observations.Chapman et a], (1982) generated relativemeasures of the intensity of predation byfish on small crustaceans from analyses ofthe gut contents of a1 1 the common fishesof Mugu Lagoon combined with monthlydeterminations of fish abundances. Therewas no indication of responses by the preypopulation even under the particular conditionswhen an effect of the fish wouldseem most likely. Amphipod and cumaceanpopulations did not decline when the rateof their consumption by fish was highestrelative to the density of small crustaceansany more often than when the consumptionrate was low relative to preydensity,Of course, the importance of predationcan be expressed in another way. A behaviorof a prey that can be demonstratedto reduce its losses to a predator islikely to be an evolutionary adaptation topredation. Predation still might be amajor factor in the biology of an animal ,even in the absence of losses to predatorsat present, if the present immunity hasresulted from behavioral adaptations thatreduced predation. Vertical migration(nocturnal forays from the bottom or fromthe surfaces of plants into the watercolumn) by the small crustaceans of MuguLagoon (Figure 46) could be a case inpoint. Because the time spent in thewater column is always during the night,investigators el sewhere have proposed thatvertical migration could be adaptive foravoiding diurnal visual predators such asfish, Experiments conducted in MuguLagoon do not support this hypothesis,There is no clear evidence of a major rolefor predation in the biology of the smallcrustaceans in Mugu Lagoon.5.5 HIGHER TROPHlC LEVELSWe have almost no information on thetrophic interactions beyond the secondaryconsumers. Higher-1 eve1 predators areprimarily piscivorous birds and fish.Spatial segregation is obvious among themajor groups of high-level predators. Thewading fishers (Table 7), mainly heronsand egrets, confine their activitiesalmost exclusively to shallow water nearthe waterline. The aerial fishers, mainlypelicans and terns, prey on fish in thesurface layers and visible frm the air.The diving fishers, mainly grebes, mayexploit bottom-dwell ing fish in the deeperparts of the lagoon. The most importantoiscivorous fish is the Ca1 ifornia ha1 ibut(Para1 ichthys cali fornicus) (Table lo),which spends most of its time on thebottom.Observations about the feeding of thetop level predators in Mugu Lagoon aredifficult to obtain. In most cases theprey are consumed too fast to identifywhat is being eaten. We know that earedgrebes eat diarnond turbot because thebirds have such a hard time eating them;however, we know nothing about the meals(if any) that went down easier. Also,gulls and terns obviously eat topsmeltbecause they stick so far out of thebills, but we know nothing about thebi rds' predation on other fishes.One possible indication of an overalleffect of top predators on populations ofthe most common species of fish is thenumerical decline of fish in our catchesin the few months after their peakabundances (Figure 351, Assuming thatmortality is the major source of numericalchange (an untested assumption) and thatpredation is the major cause of mortal i tyin this period, fishes big enough to becaught with our seine decline %20% permonth (Figure 47). With the exception of

Figure 46. Plankton samples col Iected in the eastern arm of MuguLagoon at: approximately hourly intervals on 7-8 August 1978. Tideheight was rneast~rcd frorn low water in the eartern ann. Reduced abundancesbetween 10 p.m. and 2 a.m. correspond to increased tide currentvelocl ties (from Chapman et a1 . 1982).staghorn sculpfn, the rates af mortalj tiesappedr to be constant frm rnonth to monthand simflar between species.The two major categories of predators -bf rds and Fish - have a cornlrBn high nlobilitythroughaut life and relatively long1 ives, These character1 stics free thepredators frmn controls that the es tuarineenviromnent vtould impose if they wereconstrained to be full -ti~tte residents.k4uwcvcr, here the resefnbl ance ceases. The1dgout-i is at oppasite teni~ini for bird andFish r~iSgrations. The Arctic imposesstrcict searonali ty on the birds. It yrovfdesincredibly rich Food far the rearingof young but prohlblts the presence ofbirds in the winter, A1 though prey tendto be more abundant and airnost certainlyinore productive during the surnrwr in lvluguLagoon, the even greater rfchness of theArctSc during this season is a sufficientinducement for bird.; Lo rps~ that env'nrorimentwhen it can tr@ used, As a result,larger popul atlons are rnaintained, and thebirds are a rnajor influence on the structureof the Mugu Lagoon estuarine scosysternwithout befng obviously subject to itscanstraints.In contrast, Mugu Lagoon rmy be for thefishes what the Arctic is for the birds:~wch better than the adjacent ocean forsurv'lval and growth of young during thesurnnEr ht worse in the winter. Probablythe lagoon is at its most Inhospitable Forfishes during major winter stonns becauseof temporarily low salinity, high turbid-I ty and occasional ly wf despread ~nortal i tyof invertebrates ; however, the prevalenceof Ffsh-eating birds could be a majorfactor as well, If predatian by birds isresponsfble For much of the 20% per monthlosses suggested by populatian changes inthe sumr (Figure 47), fish might haveample cause to vacate the lagoon in win-ter, hen the fish-eatSnbirds are evenngre aburidartt {FSgure 38 4 . Whatever thecause, ~atches were an order of mgnitudeless in Decmkr, January, and February

California killifishCalifornia halibutrBgbz - 20°/0 \A M J J A S O N 5 JFigure 47. Monthly changes in fish abundances in the eastern arm ofMugu Lagoon after the month of peak abundance for five of the commonspecies. Based on the 5-year means for all stations combined.than they were in June, the month of peak Predators are relatively scarce, (3) Temabundance(Figure 35). peratures are high (see Chapter 2).Except for temperature, comparable datafor adjacent coastal waters are not avail-In the summer, three factors probably able; however, invertebrate abundances aremake the lagoon superior to the adjacent unlikely to be as dense outside as inslde,ocean as an environment for fish (at least and large piscivorous fish certainly aresmall fish): (1) Food is abundant, (2) present outside the lagoon but almost

nwer inside, lower predatjon on earlystages will dllow a higher proportion of apopulation to survive these vulnerablelife stages. Higher food densities wj13increase growth rates. Higher tcmperatureswill further increase the rate ofgrowth and developinent, Individuals maybe larger than they would be wdthout theirstay in the lagoon, Presunrabfy they willk less vulnerable to many kinds of yredatorsin coastal waters kcause of their'larger size. They rnay also siarvlvcl a periodof low food better,In Pktgu lagoon less than 1% of tilc fishcaught are greater than 20 crn long (Qnufand Quamm~n, unpubl. data). The onlyrelatively catnon species caught as large5ndividuals is the shovelnose gui tarfish(Rhinoba tos ) a fascinatings-cdreat the end of thissection, The ten most cmrtun speciesaccount for over 481 of the total catchand use the laaoon to varvfrin deurees.The Cali fornfa

Table 13. The utilization of the eastern am of Hugu Lagoon by the 10 most cmmnlycaught fish species in 5 years of sampling (Onuf and Quammen 1983; see also Figure 35).Rank order byUse of Mugu Lagoonabundance in PermanentSpecies total catch residence Use consistent with a nursery functionTopsmel t 1Shiner surf perch 2Staghorn scul pin 3Large adults spawn in early spring, smalladults spawn in summer, young of yearreach catchable size in autumn.Adults give birth in the lagoon and leave,young stay only briefly.Only young of the year present in thelagoon,California killifish 4Gal iforna ha1 ibut 5Diamond turbot 6Long jaw mudsuc ker 7Bay pipefish 8California tonguef ish 9Speckled sanddab 10xYoung of year predominant in the lagoon(,80%).Apparently, adults only leave the lagoonbriefly to spawn and die.Only young of year present in the lagoon,Only young of year present in the lagoon.are found in the lagoon only as very largeadults (Onuf et ale 1979; DuBois 1981).Several hundred individuals enter theeastern arm of Mugu Lagoon in April eachyear, where they congregate in densegroups for several months and then depar~in September. Of 370 different individualscaught in 1979, 335 were females(90%) and were much larger than individuals typically encountered offshore (Baxter1974). Of 335 females tagged in 1979,136 were recaptured in less intensive samplingover the next 2 years. Almost allfemales were carrying developing embryos ;however, the embryos were fewer and muchlarger than reported for pregnant femalescaught offshore. Finally, the guts of a1 1females examined were virtually empty, regardlessof time of capture, nor were anyeffects of predation detectable in anexcl osure experiment run where the guitarfishwere observed most frequently.The guitarfish, then, does not use theestuary either as a haven for its youngor as a feeding ground. The explanationfor its puzzling behavior may be thatthe higher suinmer temperatures in thelagoon than in the ocean are beneficialor even necessary for the development ofembryos (Onuf et al. 1979). Observationsof distribution and movement of shovel -nose guitarfish were consistent withthe hypothesis that they were in thelagoon during the summer to take advantageof higher water temperatures there( DuBois 1981). Temperatures were higherinside the lagoon than immediately outside,dnd within the lagoon the guitarfishshifted from shallow areas in the

day to deeper areas at night in accordancewith higher water temperatures(Section 2.41. However, no informationis available on whether the rates ofdevelopment of embryos are tmperatureorsi re-dependent.5.6 NUTRIENTSSince no research on nutrient supply,availability, utilization, or cycling hasbeen conducted in Mugu Lagoon, features ofthe nutrient regime must be inferred fromother character-i stics of the ecosystem.Consequently, consideration of nutrientshas been deferred until most of the otherinformation about the ecosystem has beenpresented, and the di scussion is necessarilyspeculative.The major sources of nutrients to theprimary producers of the estuarine ecosystemare inputs from the watershedcarried primarily by freshwater, inputsfrom the ocean carried by tidal movementsof coastal waters, and regeneration ofnutrients from the organic matter producedwithin the system or by organisms movinginto the estuary. Much of the high biologicalproductivity of other estuaries isattributed to the nutrient subsidy fromfreshwater input. The climate of theregion and the geometry of Mugu Lagoon actto reduce any nutrient subsidy from thewatershed. Precipitation (Figure 5b),streamflow (Figure 7), and consequentlythe potential for freshwater inputs to theestuary are concentrated in the coldest(Figure 5a), darkest (Figure 9) monthswhen the smal lest amount of photosyntheticbiomass is present (Figures 24, 26, 29).Thus, the timing of freshwater inputs iswhen the ability for uptake by plants islowest, In addition, slnce the long axisof the lagoon is perpendicular to theinlet stream, and the mouth of the lagoonis immediately opposite the mouth of thestream (Figure lo), the freshwater and itsload of nutrients bypass most of the ecosystema1 together.Nutrient inputs to Mugu Lagoon fran theocean may be low too. Characteristically,the waters of the continental she1 fsustain much higher levels of primaryproduction than oceanic water. In thevicinity of Mugu Lagoon, the shelf isnarrow (5 - 15 km), and a submarinecanyon cuts across most of it, so thatthe water is 180 m deep only 2.5 kc) fromthe mouth. The clarity of water thatenters Mugu Lagoon on rising tides indicatesthat the water comes from thiscanyon much of the time.The remaining major nutrient inputs forprimary producers in Mugu Lagoon resultfrom the activities of consumers. Thesame physical and microbial processes thatbreak down macrophytes into detritus ininteractions with primary consumers areresponsible for most of the regenerationor fixation of nutrients as well. Thelarge number of seals and birds that usethe lagoon as a resting place but feed inother shore or aquatic environments (Chapter4) could import substantial quantitiesof nutrients into the lagoon. Both ofthese sources are concentrated in subtidalareas and intertidal flats.In many coastal wetlands, high biomassand production of salt-marsh plants areassociated with ample tidal flushing. InMugu Lagoon, low biomass and production ofsal t-marsh plants are characteristic ofthe well-fl ushed eastern arm, while saltmarshvegetation is denser, taller, andmore luxuriant in the we1 1-fl ushed westernarm (pers. observ.). This may be due to acombination of both less flooding by saltwaterand higher freshwater input andnutrient enrichment from sources in thewatershed. An additional explanation ofthe difference may be that nutrient-pooroceanic waters are sapping the salt marshof its nutrients in Mugu Lagoon, whilericher coastal waters provide a nutrientsubsidy to salt marshes in many otherareas. No measurements of dissolvedmaterials have been made to determinenutrient fluxes; however, the virtualabsence of a litter layer in the marshesof the eastern arm suggests that particulatematter is rapidly removed. Consequently,the nutrients regenerated bydecomposition of marsh litter are firstmade available and probably used in otherenvironments, such as the intertidal flatsand subtidal areas of the lagoon. Presumably,more of the litter decomposes inplace in the western arm. Where a1 lochthonausnutrient inputs are low, proximi tyto regenerated nutrients would then resultin higher biomass and production.

According to this conceptual model oft$e nutrient regime of Muyu Lagoon, allinputs to the saf t it~r-sh are si~lall inthe eastern ann, whereas at least nutrier>tregeneration, and perzrh~ps importsby animiis that feed outside the lagoon,cons iderahi y augment the avail abil i ty ofnutrients to primary producers in subtidaldv-eas and on intertidal flats. Thus,riutrient availability could account fortile ginding of Dnuf et al, (1979) thatsal t-.ilarsh productivity in vie eastern an?of Rugu Lagoon Mas low cornpared to othersites at similar latitudes, whrle benthicrnicrot 17v'dl productjvi ty was similar.41 thoucjn the few ava it able ot\serva tionsare cons 1 stcnt with our corlterltion thata1 lochthonous nutrient 1 nputs 'ire low andthe importance of reg en^^-ated nutrientsfor plant growth is corrrsporld~ngly high,a1 1 interpretdtions dbo the nutrientceyinle of Mugu 1-aqoan a untested hypotheses.5.7 AN ECOLOGICAL OVERVIEWThe diversity of biotic interactions inthe f9ugu Lagoon estuarine ecosystm istruly irrirnense. Earlier we alluded to thevariety, steepness, and variability of thephysicdl gradients that intersect withinestuaries to account for their bioticrichness. In this chapter we have examinedin detail how organisms in the sameand different trophic levels interact withsometin~es subtle di fferences in the physicalenvi ronrnent to produce di f ferent outcanes.These specific case histories andthe Inare general patterns extracted fromthan provide the fullest appreciation ofhow the ecosystem actually functions; however,the detail is overwhelming. It precludesobtaining a sense of the structureof the whole. Were we su;nmarize only themost proininent features of each trophiclevel.Total primary product ion is relativelysimilar across the major physiographicunits of the estuarine ecosystm, fransubtidal areas and intertidal flatsthrough a1 1 but the highest part of thesalt marsh. However, primary producersdiffer enormously in structural characteristic

diversity results. In any small area,different primary consumers will be in thewater column, on the surfaces of plants,on hard surfaces, on loose sediments, orat different depths in the sediments.Those species studied that coexist withinthe same narrowly defined spatial environmentinteract strongly, and thus, tend tobe separated horizontal ly, Physicalinterference commonly is the mechanism bywhich one species excludes another withinthe same stratum. Species in differentstrata have little demonstrable effect oneach other, even though they consume thesame kind of food.A greater variety of food is availableto the predators than to the primary consumers,and this is reflected in greaterdifferentiation of diets. Nevertheless,spatial relations continue to be veryimportant, often not correlated with thedistribution of prey. Thus, neither substratetexture (over broad 1 imits) nor thedistinction between intertidal flats andadjacent subtidal areas appear to influencethe polychaete prey of shorebirds(directly), but both are critical factorsin determining the effect of the shorebirds,The outstanding characteristic of thetop predators is their timing. Whereasconsiderable feedback between trophiclevels was evident lower in the food web(primary consumers eat plants, consumersregenerate nutrients for plants), thepredators operate outside the control ofother trophic levels within the ecosystemby migrating. This allows much heavierexploitation of food while predators arepresent than would be possible if theywere dependent on the lagoon all of thetime. The periodic relaxation of predationand recovery of prey populations hasthe effect of increasing the like1 i hood ofan abundant food supply at the beginningof the next period of residence.

CHAPTER 6. COMPARISONS6.1 GEOGRAPHIC VARlATlON IN COASTALCLIMATE AND TOPOGRAPHYThe principal natural characteristicsof the coastal regions of the UnitedStates that most influence estuarineecosystems are coastal topography, theamount and timing of precipitation, temperature,and sunlight. For its entirelength, the Pacific coast is very steep,with small coastal watersheds (except fornorthern San Francisco Bay and the ColumbiaRiver, into which are funneled watersfrom extensive areas of high elevationinland of the Coast Range) (Figures 1,48a). The continental shelf is narrow.Precipitation is heavily concentrated inthe coldest months of the year and increasesnorthward from 26 cm per year atSan Diego, California, to greater than250 un in three coastal locations betweenthe Oregon-Cal i forni a border and thenorthern tip of the Olympic Peninsula(Figure 48b). The timing of river runoffis closely correlated with precipitation,except in the drainages of the ColumbiaRiver and northern San Francisco Bay,where much of the precipitation is storedas snowpack and released much later (Figure48b). The growing season is longalong the whole coast (Figure 48c), butthe Pacific Northwest receives one-thi rdless solar radiation than southern California(Figure 48d), and evaporation isless than one-ha1 f (Figure 48e).With the exception of similar southnorthgradients in solar radiation andevaporation (Bal dwin 1974) and therugged topography of New England, thenatural characteristics of the othercoastal regions of the United States thatinfluence estuarine ecosystems di fferdrastical ly from those just described.Most importantly, precipitation isgreater than 100 cm per year frm easternTexas to the Canadian border and evensouthern Texas received at least twice asmuch precipitation as southern Cal i fornia(Bal dwi n 1974). Furthermore, the preci p-itation is either concentrated in thewarm months or evenly distributedthroughout the year. River runoff ismaximal in the spring and remains substantialthrough midsummer (van derLeeden 1975). A long series of barrierislands buffer the effects of the openocean on inner coastal waters. Here thewhole coastal region behind the barrierislands is an estuarine ecosystem. Thecontinental shelf is broad fran Mexico toCanada, and the coastal plain is broadfran Mexico to New York. By opening ontobroad expanses of shall ow coastal waters,eastern estuaries are linked to a greaterextent than is possible on the Pacificcoast.The net effect of these factors insouthern California is as described indetail for Mugu Lagoon. Estuaries hereare small and discrete, separated fromothers by sometimes 'long distances ofopen coastal waters with a strong oceanicinfluence, rather than shal low waterlying above a broad continental shelf.Precipitation and river runoff, includingthe river's supply of nutrients, virtuallycease before the period of highplant growth in May through August; atthe same time, evaporation rates arehigh. The combination of low nutrientsupply and high and increasing soilsalinities when maximal growth should beoccurring probably reduce the productivityof the fringing marshes considerablycanpared to what otherwise might be possible.These constraints on plant growthdo not exist on tidal flats and in subtidalareas. However, the virtualabsence of a sal i ni ty gradient duringmost of the year restricts some uses of

id RELIEF MAPcm10Mr104Columbia River0 0mpqua River0Sacramento andSan Joaquin RiversSan Joaquin RiverLos Angeles Rivernormal monthlyprecipitation (cm)mean monthly7. river dischargeFigure 48. The Pacific coast of North America from 30" to 50°N. (a) Physical relief,showing the rugged topography of the coastal region and the narrow continental shelf.(b) Normal rnonthly total precipitation (cm), mean monthly river discharge (m3/s) forthe estuary and the presence of somekinds of organisms. Most importantly, norefuge from natural enemies is availablethrough differential tolerance to lowsalinitywaters, one imputed source ofthe high value of estuaries as nurseryartas for some species (Douglas andStroud 1971).Despite a somewhat similar topography,the climatic differences of the PacificNorthwest lead to differences in estuarinefunctioning. Since evaporation ismuch less than in the south (Figure 48e),stressful soil salinities are less1 i kely, but less light (Figure 48d),lower temperatures, and maximal plantgrowth out of phase with nutrients suppliedby river runoff, as in the PacificSouthwest, suggest that the productivityof the salt marshes may not differ appreciablyin the north. Since river runoffdoes not cease a1 together in the summer(Figure 48b), an enhanced nursery functionis possible canpared to the south,but the rugged topography stif 1 assuresthat the estuaries are small and discrete.

C GROWING SEASONd SOLAR AADlATiON\ 1Frost-free oeriods Idavs) Solar radiation (Langleys) Pan evaporation (cm)different drainages, and mean annual total precipitation (cm). (c) Growing season(frost-free period in days). (d) Mean daily solar radiation (Langleys). (e) Meanannual pan evaporation (cm). (a-adapted fral U.S. Geological Survey 1974; b toe-Baldwin 1974; b-Kahrl 1978 and van der Leeden 1975.)As noted previously, the biologicalcharacteristics of northern San FranciscoBay and the Columbia River estuary arenot constrained by the timing of freshwaterinput, which occurs in spring andsummer when reduced salinity would contributemost to plant growth and use ofthe estuaries by juvenile stages of fishand invertebrates.On the east coast, topographic factorsgreatly expand the influence of estuarineconditions. In add! tion, the timing ofprecipitation and river runoff coincidewith the period of maximal plant growth.Therefore, stressful conditions of soilsal ini ty are minimized, and nutrientsfrom terrestrial sources are made availableto marsh plants at the most appropriatetime.This suggests that the increases in thelength of the growing season and theamount of solar radiation from north tosouth will result in relatively high productivityof sallt marsh plants in thenorth and very high productivity in thesouth, compared to other regions. The

shorter growing season (frost-free period)of New England, as compared to thePacific Northwest (Bal dwin 1974), mayresult in somewhat lower productivity ofMew England sa1 t marshes, but the differencein the length of the growing seasonis partly canpensated by very low lightearly in the growing season and low temperatureat the peak of the growingseason in the Pacific Northwest. Thenursery function is great by all criteria,including some not discussed inthe rest of this inter-regional canparison:abundant food supplies, high temperature,and protection from naturalenemies ,Despi te simi 1 ar long growi ng seasonsand solar radiation, the productivity ofsalt marsh macrophytes is much lower inthe arid Southwest than in the moistSoutheast (Zedler et a1 . 1978; Onuf et a1 .1979; however, a1 so see Ei 1 ers 1981).South to north gradients in salt marshproductivity on the two coasts also pointto an important effect of the lack offreshwater input to account for the conditions observed in southern Gal ifornia.On the Atlantic coast, where freshwaterinput varies little fran the southernmosttip of Florida to the Canadian border(Baldwin 1974; van der Leeden 1975),a strong decreasing gradient in productivitywith increasing latitude has longbeen recognized (Turner 1976). In contrast,on the Pacific coast, where precipitationincreases from less than onefourthof that of the Atlantic coast nearthe Mexi can border to substantially morethan anywhere on the Atlantic coast fromnorthern California to the Canadian border,sal t-marsh productlvi ty decreaseslittle, if at all, at least from southerrmost;California to central Oregon(Macdonald and Barbour 1974; Onuf et al.1979; Ellers 1981; Josselyn 1983;Seliskar and Gallagher 1983). This suggeststhat greater freshwater input mightk cwensating for lower light and temperaturegoing northward on the Pacificcoas t ,Zedler (1982) stated we1 1 the reasons tobelieve that the high soil salinities ofthe long summer drought period are responsiblefor limiting growth and productivityin southern Cal i forni a sal t marshes;however, the observa t.i ons presented abovedo not dl'stingui sh &ether another consequenceof 1 ittle freshwater Snput duringthe growing season 4s nutrient limitationof growth. Nor do those observations testthe imputed importance of timing. As itstands, we can be quite certain thatfreshwater input is an important determinantof how salt marshes functionin southern California and the mstimportant determinant of differencesbetween salt marshes in southern Californiaand other regions of the UnitedStates. The mechanism- behind this, however,is unknown.6.2 COMPARISON OF MUGU LAGOON TOTHE OTHER SOUTHERN CALIFORNIAESTUARIESThe great variety of coastal wetlandsin similar natural environmental settingsin southern California has three obviouscauses: size, connection with the ocean,and man-caused a1 terations . Perhaps mostimportant is that the setting is nolonger natural (Zedler 1982). Probablyevery estuarine ecosystem in southernCal i fornia has undergone major a1 terationsas a result of human activities.Portions of many have been dredged toprovide ports and marinas, while otherportions have been filled to provide airportsand space for real-estate development.Marshes have been diked for amu1 ti tude of reasons, ranging from exploitationof petroleum reserves to manage-ment of waterfowl populations. Channel shave been deepened and realigned, primarilyfor flood control and navigation.Highways and railroads have been builtacross most coastal wetlands, perhapspre-empting little area, but always alteringcirculation and often restrictingthe location of the mouth. Dams havebeen built on many of the inlet streams,intercepting sediments, diverting water,and altering the timing of water deliveryto the estuary. Land-use practices,particularly agriculture, have acceleratederosion and, through drainage of waterused in irrigation, altered the timing ofthe delivery of water to estuaries.The other two factors, size and communicationwith the ocean, undoubtedly ledto great differences among estuariesunder natural conditions, but also are

affected by human modifications. Thephysical environment (Carpel an 1969), thefloras and primary productivity (Zedler1982), and the faunas (Mudie et al. 1974)are very different depending on thefrequency, timing, and duration of asurface-water connection between theestuary and the ocean, The reason thatestuaries differ in their water connectionsto the ocean is that the longshoredrift of sand (described in Chapter 3 inthe context of inlet migration) happensalmost a1 1 of the time and tends to fillin any opening to an estuary. Unlesssufficient flow into or out of the estuarycounteracts this filling, the mouthwill close. The two sources of flow aretidal currents and river or creek discharge.Estuaries with a large areasubject to tidal change in depth willa1 ways remain open, hence the importanceof the size of the estuary. Somewhatsmaller estuaries may be open most of thetime, but, once closed, probably requirethe winter high flow of inlet streams toreopen them. Smaller estuaries willdiffer among themselves and within andbetween years, depending on their relationsto freshwater sources. They canrange fran being fresh almost all of thetime to being brackish at the time ofclosure and then becoming hypersaline asevaporation proceeds.Detailed canparisons are possible forsome important features of structure andfunction between Mugu Lagoon and threeother small southern California estuarinesystems: Anaheim Bay, Upper Newport Bay,and Tijuana Estuary (Figure 49). Althoughall have been modified by humanactivities, they have in common continuous,or close to continuous, connectionswith the ocean, relatively large size byregional standards, a variety of littledisturbedsubtidal and intertidal habitats,and natural associations betwctenmost habitats (for instance, broad flatsbetween mergent marsh and shallow openwater). Comparisons among these es tuariestest the validity of the analysisof estuarine ecosystem function developedin this profile, based on Mugu Lagoonalone, and extend the analysis to situationsnot specifically studied in MuguLagoon.Tijuana Estuary (Figure 49h) is theonly site in southern California besidesMugu Lagoon where an integrated efforthas been made to assess the contributionsof di fferent sources of primary production(Zedler et al. 1978; Zedler 1982).The two systems are similar in therelatively 1 ow productivity of the vascu-lar plants of their salt marshes (comparedto other regions) and the proportionatelygreat contribution of thebenthic microflora to total production.The two systems differ in the virtualabsence of :partina from Mugu 1-agoon andits domination of the lower marsh atTijuana Estuary, the very low productivityof vascular plants in the l~wer marshat Mugu Lagoon, and in the relativelybroad continental shel f contiguous toTijuana Estuary, rather than the narrowshelf cut by a submarine canyon as atMugu Lagoon. A1 though dredging el iminatedmost of the cordgrass that once waspresent in Mugu Lagoon (Macdonald andBarbour 19741, this activity did notaffect the areas studied in the easternarm. There, the absence of major freshwaterinputs until recent times, and theshort duration of these inputs even now,probably preclude the establishment ofcordgrass, because germination and earlygrowth appear to require reduced salinities(Zedler 1982, pers. cuinm.).In Chapter 5, the submarine canyon cuttingacross the already narrow continentalshelf at Mugu Lagoon (Figure 13b) washypothesized to del iver nutrient-poor oceanicwater into the lagoon during tidalexchange to account for the low productivityof the marsh in the well-flushedeastern arm. Instead, Ti juana Estuary(Figure 49b) is flushed by water fran amuch broader segment of continental shelfand consequently may be richer in nutrients.The twofold difference in lowmarsh productivity between the two estuaries(Figure 50) is consistent with thispresumed difference in their nutrientregimes.Six species accounted for 94% of allshel 1 ed macroinvertebrates col lectd byPeterson (1975) during 3 years of samplingin the sandy subtidal areas of MuguLagoon (Table 121, The same six speciesaccounted for 83% of all individualscollected in similar habitats at Tijuana

Figure 5Q. Priindry product ivi ty as~nc?ac;urcd by August hiornass of the lowerrqnrshes at fijuana Fstuary (from Zedler1982) and Mugu Lagoon.Estudr-y dirring the same period, H~wever,the two llrtost common species at PfuguLdsoon (the cmmensal s Cal lianassa cal i------ forniensis and-califor*)were very rare at Estuary. Dwringthe study of the invertebrates, andctive bait fishery For the ghost shrimp-- Call ianassa was in progress, using pumpspowered tsy gasal ine engines to flush Calljaridssaout of its burrows (~ete';.sonP1537gr-of course, the rernoval of Cal lijinassaalso doomed its canrnensal~egnrYptanla. There were greater densitiesof-deep-dwelling Nuttallia andTagelus (in the same stratum of the sedirlentsas Cal lianassa and Cr tm a),cotijiled withi-rightly l o e l -ties of shallow-dwelling Protathaca andDendraster at Tijuana Estuary cmpared toMunu taooon. This aattern is consfstentwi ih ~kcrson's (1477) hypothesis thatconlpetitjan For .;pace is instrumental indeternilning the structure of this benthlccanmunity, and that bioloylcal interactlonsare stronyct.;t wlthin the same depthstratum (see Chapter 5).Table 12. The mean densities (numbcr/m2) of the canmonshelled ~nacroinvertebratcs and their percent of totaldensity in subtidal sandy areas.of Mugu Lagoon and TijuanaEstuary sampled at 4-month intervals between July 1969 and,July 1972 (adapted frtm Peterson 1975). C = crustacean, E =echr"nodemr, no notation = bivalve.------- --."MacroinvertcbratcTi juanaMugu Lagoon Estuarynensi ty X Density %Cr tom a cdlifornica&'iT?n~ftnsir *- (c)TFZZGaC-stam1nea-Nuttallid (Sanguinolaria) --nuttal li S--- ifendraster excentricus -( ~ jTagel us cai i fornianusA1 1 othersTotal

Although the methods of collection differedbetween locations, sufficient dataexist to compare the fish faunas amongthe four large, permanently open, notcomplete1 y artificial estuarine systemsof southern California (Table 13). NuguLagoon, Tijuana Estuary and Anaheim Bayresemble each other closely. Topsmelt isthe numerical dominant in a1 l three wetlands,and staghorn sculpin, Californiakillifish, California halibut, and diamondturbot are all abundant in each wetland.Probably the lack of wide expansesof permanent open water in Tijuana Estuary(Figure 49b) accounts for the rarityof shiner surfperch there. The diamondTable 13. Ranking of abundances of common fish species in four large southern Californiacoastal wetlands.Speci esUpper Newport BayMugu a Tijuanab Anaheim Li ttoralLagoon Estuary Bay 1974-75d 1978-7ge q1974-75Topsmel t(Atherinops affinis)Shiner s u r f o e r r2(Le tocottus armatus)3Ca , ~ I w(Fundulus parvipinnis) 4California ha1 ibut(Hypsopsetta gut tula ta ) 6Arrow goby(Clevelandia -) *Striped mu1 let(Mu il ce halus)Deep -$s+ o y anc ovy(Anchoa canpressa)Slough anchovy{Anchoa delicatissima) 3~os-i: h(Gambusia affinis)81 a m e r(Efirbiotoca jacksoni ) 2Round-+stingray(Urolo hus halleri)White sur perch5(Phanerodon furcdtus f-- 6abOnuf and Quamrnen (1983).White et al. (unpubl. rep.).CLane and Hill (1975).d~i len ( 1976).e41 len (1980),*Probably much mre abundant than any other species, but inadequately sampled by gearused,

turbot is relatively more common atAnaheim Bay than at the other locations,but the reasons for this are not known.Two features distinguish Upper NewportBay from the other locations. The bay islarge enough that the fish fauna of itsopen-water areas is distinctly dl fferentfrom that of its littoral areas (Figure49c). Surfperch and flatfish characterizethe former, while topsmelt, killifish,and sculpin typify the latter. Anchoviesoccur in both areas. Although some ofthis differentiation can be detectedat Mugu Lagoon (Tables 5, 6) and in AnaheimBay (Lane and Hi1 l 1975), the spatialseparation between open water and littoralareas is rather small, and topsmel t is nota 1 i ttoral species. The cther distinctivefeature of Newport Bay is the abundance ofmosquitofish (a primarill freshwater species)in the littoral zone in 1978, one ofthe major storm years that figured soimportantly in the analysis of ecosystemfunction for Mugu Lagoon. At UpperNewport Bay, shiner surfperch and staghornsculpin were more abundant in the dryperiod sampled (1974-75) than the wetperiod (1978-79). Shiner surfperch a1 sodeclined at Muqu Laqoon in the 1978-79wet period; however, -staghorn scul pin didnot decline, and no freshwater fisheswere caught there in the wet period,Whether both differences arise frm agreater freshwater influence in UpperNewport Bay is uncertain. Eggs andlarvae of staghorn sculpin in TomalesBay, California cannot survive salinities

more extravagant extrapol a tions requi red ences should a1 1 ow the extension of theto synthesize a complete analysis for basic analysis to a broader array of con-Mugu Lagoon. Furthermore, those differ- di tions, as out1 ined above.Figure 51. Smaller estuaries of southern California, always open butonly indirectly connected to ocean or with altered relations betweenhabitats ~sithin the estuary: (a) Agrra Hebionda, (b) Upper Botsa Bay(the State Ecological Reserve), (cf Carpinferia Slough, and (d) GoletaSlough; or unpredictably open to the ocean: (e) Los PeWasquitos Lagoon.

CHAPTER 7. MANAGEMENT CORII$IDERABIOMSIn southern California, encroachrnentson estuarine systems have been so severethat we cannot really know what thesesystems were like and how they functionedbefore the appearance of rnan in theregion. In that sense, the remnants ofestuaries are not "natural" (i.e.,intactexamples of a whole ecosystem). On theother hand, the estuarine realm wherefreshwater, marine, and terrestrialinfluences cmmingl e a1 ways has beensubject to a wider range of fluctuatinginputs and conditions than almost anyother ecosystem. Consequently, many ofthe alterations caused by human activitieslie within the range of conditionsexperienced by the natural system. Thus,many of the remaining parts of estuariesin southern Cal i fornia today probably hadcounterparts in estuaries before hunaninfluence.Unfortunately , the proportionate contributionsof different parts of estuarineecosystems in southern Californiahave been altered so drastically that wecan not even guess what the naturdl proportionsrnight have been. Some parts ortheir connections to the rest of theestuarine ecosystem have been a1 mos tentirely el iminated. Functions thatdepended on those parts or connectionsinevitably have been elimindted or drasticallycurtailed. The most obvious ofthese are the elimination of most freshl~atermarshes, the separation of most ofthe remaining freshwater marshes fromtidal wetlands by levees or roads andrail road embankments, and the consequentelimination of brackish water habitat$.For waterfowl, part of this loss has Szenrllade good by purposeful manageinent ofimpounded areas of freshwater for theenttance~:eat of yam bi rD popul ation5 .However, if a nursery function everexisted based on a gradual transitionfran freshwater to seawater, it has beenlost in its entirety. Clearly, the wholeis not what it once was. Nevertheless,the remainder continues to be a densemosaic of natural habitats, all the rnoredeserving of protection and carefulmanagement for educational , scientific,and aesthetic purposes because of theirproxirni ty to densely populated areas (Onufet al. 1979), in addition to their incalculableprimary value in support of endangeredspecies and as habitat islands forother sensitive wi1 dl ife.The main concerns in managing the survivingsmall rennants of estuarine ecosystemsin southern California are protectingthose remnants from the impactsthey can not tolerate (for instance, highlevels of sedimentation), restoringdegraded areas, and responding to theneeds of endangered species. The Navy'srole in protecting the natural resourcesof the Mugu Lagoon estuarine ecosystem issummarized in the next section. Somespecific concerns about management thathave arisen in this report are then addressed:(1) sedimentation, (2) otherwater-borne contar~inants, (3) a1 tera tionof tidal flushing, (4) endangered species,and (5) infornation gaps.7.1 PROTECTIONBecause it is enclosed by a militarybase, Mugu Lagoon is well protected fromfurther development pressure. Pub1 icaccess to sensitive natural areas isquite restricted for mil i tary securityreasons, and even scientific researchrequests are carefully screened by a reviewboard to avoid potential impacts tothe ecosysten. in 1963, the Havy enteredinto an agreei~ent with the Fish and Wildii fe Service and the Cal i fornia Department

of F2sh and Game to fonnulatc n fish sr!dwildlife ndnaqement pt&n to allow dndprmote pres2rvation of the ecn(3y~trn andIts speclcs arzzwblatje. Thl% Cooperdti~c.Plan w updated in 1976 wftk tkaa,csdoption of a Fdrh and Hildlife ManaqcmcntPlant for the Navy bnse and nearby5an Nictllas Island. With the recentestabljskment ag the Siantd t"donlca %untadns Natlona l Recr~ntlon Area, the Ihvyand the Park ServCbc entered into dninternyency dgreetnent for ndndqeinent ofthe edstern am1 and ctrrrtral 1.~5511. Thecs~parti af the lagoon are IncIudwf 4n theNatlonal Recreatfon Ar~a t ~ l l renaln Navyproperty dnd under Navy control,MJlilfLary rriandyemrv~~t hds czansir;t~d ofact%vc* corrservatf on of the naturdl resourcesof the 1 aycrun and t t~ ntat t dnds ,wf th pronjatfon of rc.c;e.nrch fnPn the ccslogfcal strbcctt~re and functioning of thelag~sn and fts PrOncj"lnc) wctlandr, by N~vybfslagist~, and other %cfenCfstc;. tdowever,much of the tnanaqeinent af the estuarymjyht be better tr?nn& ar; pawfve,that Jx, maintafnmf in Its odttirdl ~tati~.The Navy successt.ully prevented openlrtcj ofthe barriara beaches Ea, develeptwnt frr theI$&B's, snd cant i nucs to prmio ta rty fsrraldevelop~nt: corrsIg,te:nL wlth rninlinizfngSrtlpects to the laq~an, Cont tnued developmentof the wdtershlrcl otrtrftjct thp &tea oftnjl i tary or Hallofla1 Paark Scwrce cuntrtslposes the tttost pt.obdk?la tpnd %ub% trxntf $1'rmpaxctt to the e"ltfary tllrotigh thi~ threatof Incredsecl sedintr?rotdt5on, df%cuscPci f ~ nthe la1 Inwirirj wct for?.7.2 SEDIMENTATEOMck~annels drt? Plaliked by levcer, andlildjor stcrnas ln 1978 and 1gRO cdused coarse reditnents are removed in rfebrirlargeand lang-lra~tinq ct~dr~yte% Jn th~ retcntiocr basins Before enter-iny themorpt-rol oyy of the i.ctrLt-a1 i ~ t rr s dtrd east- clouyh ~harrtiet s. Thus, $nost serliirl~ntf;ttrrt dnn of Muqu Ldqoon. The t:~fltrdl bypas*% Ihr slouqhs,barlo wirs trdrtsfonned Crtnr ;r wldr rxpnn5Psf prrrfnanent open wd ter Into a pr~tdas~l- At iituqu Lnqaon, blarrlnij failure ofnentiy fnta?t.tidal arpa Sn 291R, drils ttle levees ups trcaa!, aln~ost the enti re par-tnezta Cieptt.~ dP low water 111 the easterr1am dfmfi,"thed by 159, %he decycll aareaqdec~easd irrcasl '!rt depth. Ira i980, thedeyorr i tlon sf nkw ssc3dic!rt?ntr decreasrddeptl~ of low water r\notEl~~* 17% {Figure181, 16: not for the breach'ing of d leveeon Calf eguas C~eck and thc deglcr5 f t ;I>~I oithousands uf eubfc yards of 5rdirnent.i onsad fields, the deposi tlon tbf ~edilnerrtsin the edstern ama would have kr.n cgnridernbly greater.Thr relations of tkiesr physical Smpactcon the lagoon rith chdracteristics of bRelagotw and watesshed, land use wS thin the~atershed, and the c: iir~atic cycle havebeen described earlier, The? kiolaqicalconsequences of thegc physical cbanqcshav~ k8crn a key them tiqrouqh rrwt nf C , ~ Ppreceding analysis of eco.;ystclr function,The inp1IcatJcafls for manarjw~ent are"itdrk.In fact, the cnajor ston% that fdus~dthe al terntian? desrr-ib& In thir reportarc not rare events, Four such stomsuccurr& cfithirr 20 ycarr hetwcen 1941and 1980, Judginy hy the evidence for101ig-tern: hydrrsloajiedl cycles in thcPacific Soutlwest (Figure 6) crnd thetndicatlonr that a filoi~t period has justb~cyxin (Figure 2U), It, sems very likelythdt r,tnrtrts wlitXr effects at least asscvcrc ds those of 1'1958 and IWRQ wil locmr in the near future.lhcic nk%s,rv~! tirsns ~jucjqe~i t thdt MUQUlacloon wr'll not perr,ist rwch luriger as wenow know it. As the central basin and~d.r,trm dm ffll further, I suspect thatthpy wwll l take on the fonn of a floodpfdinrdttter thdn a slough cystern, suchdxi at Cat-pinterfa and Goleta. At thoselacat ions the natural alluvial fans areat tk'rr41dndward extr~lrfiities sf the netfand5 whrra s trcatrrs orxe di sctrsarcjed, hutnow those streaiw pas5 throtrgh the wtlanrfsin rtlannels that have heen artificr'al ly wider~ed and deepened for floodcuntrol f,urpos~~,. /n most cases, theticulate load of the inlet strearns dischnrrjer;into the heart af the wetland.R~cda~%r? flood flows with their sorretimeshcilvy hux-denr of sur,pr"nded yarticulatc?merterfal and b~iedload are not canfindwfthin a'lairroiv thdnne?, they ~$11 spreadnu-r;, slow

and interactions with seawater thatcause flocculation and hasten depositionof fine particles. Therefore, ratherthan passing through a relatively longlivedintermediate stage resernbl ingCarpinteria and Goleta Sloughs, where atleast the salt marsh part of the coastalwetland ecosystem persists, I foresee therapid development of an a1 luvial fan thatengulfs the rnarsh as well as the lowerelevations of the lagoon. Because of theartificially restricted contact betweenthe western arm and the central basin,filling will be much slower in the westernam. According to projections of theSoil Conservation Servl'ce (19831, theonly wetlands that will exist by the year2030 will be a thin finger extendinginto the eastern arm and narrow corridorspassing through what now is the centralbasin to the western arm and the terminationof the channelized portion of CalleguasCreek (Figure 52).A consequence of the central and easternparts of lvlugu Lagoon prograding intoa floodplain is that the threat offlooding to the developed parts of theNaval Air Station will increase. Bydefinition, a stream overtops itsFigure 52. Topographic maps of (a) Muyu Lagoon in 1980 and (b) ds projected s'n 2030assuming present rates of filling continue for the next 50 years (from Soil ConservationService 1983).105

previous channel in its Floodplain zii,~~?riclmajar storms, When the floodplairi 4. a",elevations that exceed 5 ft *I) 145:as projected in Figure 52, ddjstcrnt developedareas at elevations 810 ft (3 iq)MSL will be in jeopardy. Thts incltrrl~smost of the facilities at Point FPi~giiNaval Air Station,I fnfer on the bdsis of these consjdsrationsthat channelfaatSon of CallegiidsCreek nil 1 be required before the conditionsdescrfbed above have been real 'r'z~d.If future containment is fnevitable, at Ihave just postulated, the wooer it isundertaken the better. Now re1 a tivcl ylarge and diverse areas of wetland habitatstill exfst fn the central bdtin dndeastern arm of Mugu Lagoon. The soonerthey can k separated frm the atonnClaws of Cal leguas Creek, the hfqger andthe more varied the area of aquatic hdbitatswill k that can k sustained (salvagedmight he rrlore apt) in the MIJ~JI~Lagoan estuarine ecosyr tern. Thcrcfore,evillua tian uf aptions to fntercept rctfimentsupstrean of Filugu Lagoon dnd %adivert floodwaters around the laqocrn(Figure 53a) should btz the highest griorftyof rwnagment OF the Mugu I,ratjoonestuarlnlz ecosystm. Even chanrrel irdtlonstrtlfght through the rntddle of MugtiCagson (P3gure 53b), If done soon enough,4s preferable Lo takfng no action untilflooding of the Navy base con~pels action.tbr? "'nzltirrdl!' "131 low wa trr enui rowlent;of t"P? lagoon, the dnvialtinc~ of thernarirle c,annectil)n #as. re-e:taljl i $bed inthe rcrk of the lagoon f~lapnrirtily. Unfortunaloty, the amount and character ofsljkbsequpnt devcl opr~ent in tho upf~eswa terr !ial probah? y akrbrcvia ted tire if fp-?pan of the Rr~1e t:onsiderahly and~5myrnrtisrrd the utfl i ty of dredqedbasins here a5 managemrnt tools in thefuture.Ttie problem of seriinlentatinn is themost: rer-lour coclccrn of nanaqprgent 1nrwst of the coastal w~tlands of soutlzernCalifornia. Unfortunatrrly, thr sources~f the prol)len lie far away frm theaffect& wetfanifs and far beyond theauthori 6-y of the dqerlcy or agencf~src~panstble for thc ritanagenent of thewetlands. Certrtinl y, nruch of the erosfanin coastal wdterrhcds that suppi 4es t h ~redirnentc; that flll coastdl wtlands $5avoidable by proper znnfnrj and institutinqland-use practices appropriate to a particularqcologfcdl srttlnq. Also cpr-Ialnly, 13n)e hrieflts would Iro realfzedIn the wntershmd as well aa Cn the wetlandif tire best practices of watershed wnaqe-!-lent were carrld out, Fertile topsoilwould tltp conserved, property n~ in tennnce(incf urffnq roads) woultl k less expensfvt?,and retentfan OF groundwater could beenhanced,The recaf~wndation to preserve wet1 dnr3resources by making naasslve structurdl The ituin nbrtdclcs to dc31itrving thesea1 Ceratlons wi thin the estuary runs sa mutually beneficial outcotrEr; are that thecounter to any perccptlon sf natural ins ti tu tiontml mchanisiqs, do not ex$ st tohabf tat ref 4 t f uns t1.m t I reyu 1 res imp1 emcnt stich nanarjertPelnr Ijragrams, andfurther explanattan. The point fs that cnfurcment wufd be dl fficul t in asqypast alteration of the inlet ~tredm SF case, Djckert et dl. (19881) developed athe fundamntal viol atiarr of na turaJ pflot pracjrm for El khorn Slough Inrelatfurrs. Cal leguas Creck wnul d not Mnolercy County. Evalui9t Son of that prodischargethe t~icajori ty of its burden OF qrm ljnd development of wafershd rmnagepart"rcui&tcttlatter irlto Fhrgt~ Lagoon if it ment programs far oth~r wetlands shauldwere not constrafniaf to do so by he undertaken as coon as possfble, fnart 1 f icf a1 levees, as the brcactle

7.3 OTHER WATER-BORNE COMTAMBsdlNANTSInformation on the water quality of theinlet streams and within Mugu Lagoon l's1 imited. In a study of Revolon Slough(Figure 53a) from October 1980 to July1981, Incan concentrations of four pol lutantswere at or above hazardous levelsfor a marine environment according to EPAcriteria: lead (approximately equal tothe EPA standard) , mercury (%?Ox), sil ver($10~)~ and methoxychlor (%20x) (SoilConservation Service 1983). RevolonSlough is the tributary of Calleguas Creekthat drains most of the intensively cultivatedpart of the Oxnard Plain, The flowof Cal leguas Creek is -3x that of RevolonSlough. Si_nce the former drains lessintensivelycultivated land, the pollutantsmay be diluted befor,? they enter thelagoon. The only determir~ations of waterqua! ity within the lagoon were confined toone location in the western arm (eightdates sampled, autumn 1974) and one in theeastern (two dates sampled, autumn 1974).Scans for 50 organic pesticides were negative,and elevated levels of heavy metalswere not detected (Baker 1976).Effluents from five sewage treatmentplants discharging into Cal leguas Creekprovide significant sources of freshwaterduring non-rainfall periods. Apparently,the only times in recent years that sewagehas been a problem followed breaks insewer mains upstream. Ordinarily, effluentsare treated to acceptable levelsbefore discharge into the Calleguas Creeksystem. Nutrients from these sources arecontrolled by the State, whereas agriculturalimpacts are not control led.These data suggest that poll utants area minor problem compared to inputs ofsediments. However, the part of thelagoon [nost susceptible to the inputs(the central basin near the mouth ofCall egua s Creek) has not been sampl ed.Also, spills upstream, such as breaks insewer mains, could affect the lagoon.The absence of sport or commercial exploitationof the lagoon's 1 iving resourceseliminates most of the human healthhazards associated with pollutants;nevertheless, the potential for waterqua1i ty problems exists and has Seen insufficientlyinvestigated.7.4 AhTERATlQN OF TIDAL FLUSHINGThe estuarine ecosystems of southernCal ifornia are differentiated first andforemost according to their extent of contactwith the ocean. The permanentlyopen, least modified wetlands are varied,usual ly densely populated ecosystems.Without doubt, tidal flushing is the mostimportant property in determining therichness of the associated ecosystem.Tidal flushing is essential to the establishmentof a broad spectrum of substratetypes. Tidal flushing produces a widevariety of exposure-inundation regimes.Tidal flushing assures that some of thephysicochernical stability of the marin,environment is imparted to this protected,shallow water environment, thusbringing the wide variety of physicalenvironrnents within the thermal, osmotic,and respiratory tolerances of many organismsexcluded from enclosed wetlands inthe southern Cal ifornia coastal region.Tidal flushing moves materials around,enabl i ng organi srns to exploit resourcesfrom areas from which the organisms areexcluded, and removes wastes that mightaccumulate to harmful 1 eve1 s.Because of the obvious benefits oftidal flushing and because of the starkcontrasts between open and closed wetlands(or the same wetland when it isopen as opposed to when it is closed),any alteration that reduces tidal flushingusually is assumed to degrade theaffected wetland. Conversely, any a1 terationthat augments tidal flushingusually is assumed to enhance the naturalresources of the affected wetland, andsuch alterations commonly are proposed torestore degraded wetlands.This was the logical basis for electingto open up the western arm of Mugu Lagoonto increased tidal flushing in compensationfor the loss of wetland habitat to amil i tary construction project. Indeed,the much earlier construction of a roadhad reduced the connection between thewestern arm and the central basin from150 m wide to five 1.5 m x 1.5 m culverts.After the augmentation of theculverts by a 32-ft single-span bridge asspecified in the restoration plan, the"normal diurnal tidal fluctuation"increased from 0.2 m to 0.7 rn, and an

additional 100 ha of sal t in;ltmih wereflooded "during man high tidal slate"(Woi f e et a1 . 1979).Little was known about the natrirai resourcesof the western ann prior to theaugmentation of tidal flushing beyi rlningin January 1979, and doubt remains as towhat was enhanced and ether anythingsuffered. One federal ly 1 isted andangeretfspecies, the salt mrsh bird'sbeak (Cord lanthus rnarititnus), occurredto tida ateration only in thewestern arm on the upper periphery of thebefore and after implmentation, so thatprior --+l critical aspects of the performance of theproject can be evaluated. Ideally, tilemarsh, and one species listed as endan- pre-project inventory should be initiatedgered by the State of California, Beld- soon enough to provide Input for the finalin9 's Savannah sparrow (Passerculus design of the project, Realizing that the+sandwichensi s beldin i ), was heavily concantratedZn t e upper part of the saltmarsh surrounding the western arm. Bothendangered species are stil l present andperhaps in greater numbers (R. Dow, pers.canm. ).The light-footed clapper rail (Rallus) historical 1-in the eastern dndcentral parts of the lagoon and farseveral years had not been observedanywhere In the lagoon. The rail wasagairi observed at hgu Lagoon starting in1983 and in increasjng numbers since then,All recent sightings have hen Sn thewestern am f R. Dow, pers. comi.).Management consideral-fons for endangeredspeclcas are discussed further in Section7,5. Unfortunately, observations on thcnlore colntrwn organi sins before tidal f 1 us h-ing in the western arm was augcnented wereinadequate to draw any concl usions aboutcf fectr of the mod4 flcation.It is clear that wc do not yet knowenough about the function of the coastalwetland ecosysteins of southern Cal i fornlato accurately predict the consequences ofdl tera tionr, Therefore, we should approachrestoration and enhancement activ i-ties wf ti) great circumspection andhuiri l i ty. Each project mrs t be treated asan experinlent at thr's early stage in thepractice of coastal wetland restoration insouthern California, with the most valuableproduct being better understanding toapply in future rnanagment rather thannecessarll y and unequi voql ly the enhancementof natural resources (Josselyn 1'482;Zedfer 1982, 1484), At the very least,the planning s$creild include a systewtirevaluation (Ijst of @ducat& CJLICSSPS) ofthe re5p;crnses of edch catqor-y rrf nahiralresources (t~ajur Functional gz-oups ofwetland oyanisms and endangered rpeei ec,' ,as we77 as the explicit identification ofthe expected prime knef iciaries of tvlea1 teratian.All future restoration projects rwst includeinventories of natural wsourcescanmiwent to project evaluation has to hecon~mwnsurate with the sire of the projectitself, the option of performing adetailed evaluation of one or a few issuesshould tx, considered and wrhaps encouragedIn small projects, when a generalassessment could only be prfunctory.Finally, tests of speclfic ideas aboutwetland function that are Rfghly relevantto restoration but are Snadequa tely documentedshould k incorporated into restorattonproject designs. For example, thelmpted Ilrn4 tatfon of salt rmrsh probuctivityby hypersalinity could be tested bypurpose1 y confining freshwater drainage tospecific parts of an othewSrre sirnflarlyconfigured restoration. Mere possibleoutcornes are controversial, bet-hedgingrnay be warranted. For instance, In arestoration plan for Cos Gerri tos wetland,bracki st) water impoundnlents were includedfor their presunted benefits to waterfowl ,but because the concmi tant increases inroosqui tos might k unacceptable inadjacent residentlal areas, a fail safe wasbuilt in. The impoundiwnt could beconverted to a rnarine intertidal area byremoving a single barrier (CaliforniaState Coastal Conservancy 1982).7.5 ENDANGERED SPECIESFive endangered species occur in MuguLagoon, One species is a plant, the saltmarsh bird's beak (S-lantRus mri timusssp. riwritinrus), and four specfes arebirds: the light-footed clapper ra?l[Ral lus fongirostris levipes), Be1 ding's

Savannah sparrow f Passerculus sandwichensisbeldinqi), California least tern-(37%6na3m marurn brwni), and Califs brown pel i

Fiaure 55. Salt marsh bird'r beakmaritirnus spp. maritimus),sy3 rJ. S, Navy.)colonies arc separated from any tidalinfluence. Tests at Mugu Lagoon indicatedthat gemination is canpletelysuppressed at salinities exceeding 12ppt, but increases after pro1 onged exposureof se@ds to cold and is greaterafter 2years of storage than whenfreshly cot lected (Murphey et al. 1981).Thus, the plant appears to be adapted toa highly variable soil salinlty regdrnethat excludes. most other plants. Presumably,the suppression of geminationexcept at taw soil salinity and enhancementof geminatton after prolonged coldbath increase the probabf 1 f ty of conr(11crtivlgdevelopment before sal fni tfes becoinetw high for even the mature plants. Qiabflityfar at least 2 years provides foravoiding a1 together growjng sedsons Inwhfch Insufficient freshening occurs.The capab31ity to parasitize other speciesmy fnsure survival under condl tionswhen salt rnarsh bf rd's beak would be competltively el iminated otherwise (abnormalpersistence of 1w soif sd'linf ties, F Q ~1 ns tance) .status is hwan disturbance of it-, highmarshhabitat, either For r~al +state~ ~ T s ~pi?erlt; ~ P J or by tramp1 i ng. The highmarsh seems to be a favors! habitat ofthe dune higgy and the dump truck, aarfthe brittle salt marsh blrd's beak isill-sui tcd to survive these invasions,even &en transient. Its vast st"ri01.1~nablraf enanies dillring observations atMugu Lagoon were leaf roller larvae(Murphey eet al. 1981), The depredationsof this herbivore might be coacenlratedon salt marsh bird's beak, abecause otherannuals of the hl'gh cnar5h habitat havevery short life cycles, whfch IMY riota1 low the lepidopteran larvae to completetheir life cycler.Sirice 1978, the kntwn mpulations ofsalt rnarsh bird's beak have been mannedeach year, and since I980 total co&r,densi ty, vigor, growth, and fnortality havebeen nloni tored himorrthly an pemanenttransects, along with wdter depth andsalinity and sail ts~pcrature, moisture,texture, and sallinity (R. now, per%.canm, ). Togc ther with ongoing laboratoryr tudies of propagation, these activitiesshould provide dn excel lent and essentf altechri-ical foundation For attenptjng torehabi 1 i ta te an endangered species, andthis augurs wet 1 For the salt marshbird's beak.The primary hahi tat sf the Ifqht-footedclapper rdil (Figure 56) is the low marshAdaptatf an to a phyys ical errv i ronr~ientthat eliminates most competitors and thehmiparasitic habit are not er~nugh toinsure a secure exi stenue, hcrwver, TIlcmain reason for the plant? sendangereiiFig~rg Ijg, tight-footed clapper- rail(ms Ionyiratitris - levi~). (USFWSphatn,r

:paytjna fo-iiota :one in four of the five,ocat~o~s &ere nlore than ten ,-ails werecounted during censuses in 1980 and 1981:Tijuana Estuary and Mission Bay Marsh inSan Diego County, and Upper Newport Bayand Anaheim Bay in Orange County (Zembaland Massey lY81a, b), Zedler (1982) providesa recent summary of the status ofthe clapper rail in these areas, whichjustifiably emphasizes the crucial roleof cordgrass for nesting and cover.Sightings of rails in Mugu Lagoon havebeen few and far between. The virtualabsence of cordgrass undoubtedly is partof the explanation, but another part issimply that systematic efforts to lucatethe birds were concentrated in the easternarm where historically they had beenrnost abundant (R. Dow, pers. cmm.). Instead,the only sightings in recent yearshave been in the western arm. In spring1983 a single rail was seen in the vicinityof a patch of freshwater marsh at theupper edge of the salt marsh, approximately400 m from the tidal flats of thelagoon, In spring 1984, at least threepairs of rails were located (R. Zembal,U.S. Fish and Wildlife Service, LagunaNiguel , Cal i fornia; pers. cmm.) . A1 1were seen near the western end of thewestern arm - on an isolated section ofold berm in the middle of Salicorniamarsh and along a tidal creek.This information is meager; however,the association with freshwater marsh maybe germane for future manageiiient. Astatewide census of light-footed clapperrail populations in 1982 showed 22% ofthe State's souulation nestinq in fresh-upland edge, since the rail's preferredhabitat of tall, dense Spartina is sorare,The other direction to look forguidance in promoting the rail populationof Mugu Lagoon is toward CarpinteriaSlough in Santa Barbara County, the fifthof the sites that supported more than tenpairs of rails in 1980 and 1981. S artinadoes not grow in Carpinteria S l o band urobabf v did not historicallv(W. ~eiren, -~niversi ty of ~al i fornia",Santa Barbara; pers. comm.). The attributesof this marsh that provide such goodhabitat for rails in the absence of Spar-- tina have not been analyzed but should be.This most northerly site in the currentdistribution of the rails probably wouldserve as a more valuable model for managementat Mugu Lagoon than the more southerlysites where Spartina is so important.Patches of freshwater marsh interdigitatewith the upland edge of the salt marsh atCarpinteria Slough, and rails are in thepatches or on their edges (pers. observ.).Also Carpinteria Slough has a welldevelopedsystem of tidal creeks, incommon with other sites where rails arerelatively abundant (Zembal and iilassey1983). More detailed comparisons shouldbe made.The Be1 ding's Savannah sparrow (Figure57) appears not to be in so perilous astate as the clapper rail, presumablybecause its preferred habitat is muchmore widespread than the rail 's. Thesparrow is found mainly in the middle andupper parts of the salt marshes, especially &ere pickleweed (Sal icorniaLaqoon should include the "Pansion aid Figure 57. aelding's Savannah sparrwprotection of patches of freshwater narsh (Passerculus sandwichensis be1 ding? j.within the salt inarsh and "ringing its (Photo court2sy of U,S. ~av~,)113

) predominates, It eats insects,seeds, and Scal icorrltg tips,19791. C a l i f o r n n snake5have been observed to be a significantpredator on sparrow eggs in the easternarm of the lagoon (S. Davls, PeppertjincUniversity, blibu, Cali fornia; pers.cm.). Massey (15179) provided an excellentaccount on most aspects of its bio-1 ogy*Mugu Lagoon supports one of the twobiggest surviving populations of theBelding 's Savannah sparrow, cons istentwith the large expanses of Sal icorni,a-marsh surrounding the lagoon. The cantrastbetween the high densfty of sparrowsIn the western arm and the low densityIn the eastern ann 4s the feature ofgreatest interest for nanagement, T~Pvalue of tYI1 s contrast for manaqer:#lntlies in the contradiction bekeen thecomtnonly perceived "degradedt' status ofthe western am (for instance, 4j.S. Fisiland WJldlife Service 1979) and the ab-vlous nuch higher carrying capacity ofthe western ann than the eastern ant1 furthis endangered species. It ranains tot>e determine$ why occurrence of theBe1 ding's Savannah sparraw violates perceptionsof degraded wetland at MuguLagoon and el sewhere (Massey 1979).7 6 IPJFORMATIBN GAPSblugu Lagoon probably has been ctudiedrrlore intensfvely than any other estuaryin southern Cal i fornla. However, irtforrnationgaps raqain, as not& throughoutthis profile, The mast imwrtant gapsare the lack of infornation ahout nutrientsand the paucity of infomation aboutthe w~rtern am, except for birds. Thelack of infomation ahout nutrientsnecessi tatd a speculative analysis ofthe influence of nutrients on the structurednd function of the rest of the eco-ryst@~?rrl, which re1 ied on inferences drawnfran the physical characteristicr of thesystm and the characteristics of primaryproducers fn different parts of the rystern.The analysis led to a series ofhypotheses ~itggestdng that ample tidalflushing might be responsible for lowsalt rrrarsh productivity in the rtdsternan11 of Mugu Lagoon. This interpretationis consistent with available tnfomationas far as that Infonnatjon goes, but isat odds with the findings in most othersystm~, Therefore, the whale topic ofnutrient supply, availability, and usemust be studled 1~Fore we can understandfunction4ng dt the base of the ecosystem.Phc andlysir Zn this profile should ktreated as a set of hypotheses, provocative[rut ds yet untested.The paucity of knowledge about theEndangered s peci es pose sorm ser 1 otls western dnn of' the lagoon 1s a criticalifil@~ms, The serfou~ strdits that they concern for the future ~nnnayetnent of theare in seem to demand that we take in- estuary for a rrurnbvr of reasons: (1) Thentczdfate actlon, yet we lrkly understand western ann and the central hasin are thetheir needs so itrrperfectly that our parts of the lagoon thdt have ken itmstactions could we1 1 prove to be detri-- impacted by past human a1 terations.tnental. Our ignorance argues for Therefore, remedial actions should beintensfvt? study, yet intensive study rr~y focused Sn these parts, (2) The ongoingnctcess 9 tate disturbance that causes Lcndc- operations of the naval base around theceptable hann to an atready btcdguered westerrz am will necesf i take other a1 terspecies,Even when an alteration is ations fn thfs part of the lagoon in theclearly knef fcial for one endangered Future, (3) If the Soil Conservationspecies, it may he detritrrenlal for Servir:e's (1983) predi ctions about sedianotherendanger& spec? es, Sf nce so aentatfon in the rest sf the estuary holdmany endangered species are concentrated true, the we~;tern arm wilt be the onlyinto the fragwnts of coastal wet1 ands part of the lagoon where estuarine habirm.r"n4ngIn southern California, these tat% will persist. (4) The activities ofconflicts are lIkely ta be frequent: and four of the five endangered species resiserious.Therefore, when a1 tera tf ons are dent l"n or using Mugu Lagoon are cancenmade,they should be conducted as cxperi- trated in the western am (salt marshmtrts, and their o$tcO:ntS sft~)ald be Sird's be&, Belblnt;'s Saua~nat: sparruw,close1 y scrut inired before the same kf nd 1 igltt-footed cf apper rail, and Cali fornf aof alteration is impl@inent& again,least tern), Since the needs of present

and future mnagement will k concentratedin the western am of the lagoon,yet little of what we now know applieswith certainty to this part 3f the ecosystem,a high priority of managementshould be the support and encouragementof ecological research in the westernarm. Although any information about thebiota and the environmental regime of thearea would be valuable, the needs of theendangered species certainly should bestudied, including comparisons with othersystems that might serve as models fordesigning habitat improvements. Currently,the Navy is supporting valuableresearch on endangered species in thewestern arm. Trade-offs for differentsegments of the biota should be evaluatedfor increasing tidal exchange. Increasedtidal exchange may mean more completedrainage of areas which could be detrimentalfor organisms dependent on surfacewater. This applies to areas that areseasonally flooded because of road bermsor dikes, as well as areas where tidalexchange is only restricted.Although considerable information hasbeen gathered on the use of the lagoon byfishes, three aspects of fish biologyrequire more attention.(1) Use of tidal creeks. No informatfonis available for Mugu Lagoon.Studies in El khorn Slough (Barry andCaill iet 1981) and Ti juana Estuary(Nordby 1982) indicated heavy use byjuveniles and especially larvae of somespecies. Thus, retention of some waterin tidal creeks should be insured whena7 tera tions to increase t ida7 exchangemight result in drainage to lower elevations,as has occurred in the westernarm.(2) Halibut nursery. The possibledependence of Caf ifornia ha1 i but, prizedby sport and commercial fishermen alike,on estuarine areas as nursery grounds(Plummer et a1. 1983) and the abundanceof halibut in the eastern arm of MuguLagoon (Chapter 4; Onuf and Quammen 1983)suggest that better information abouthabitat requirements and distribution inthe rest of the lagoon is desirable.(3) Shovelnose guitarfish nursery.The southern California fishery forsharks and other el asmobranchs hasexpanded greatly in recent years and nowincludes the taking of shovel nose gui tarfish(M. Love, Occidental College, LosAngeles, California; pers. comm.). Theconcentration in Mugu Lagoon of verylarge females, carrying large eggs andembryos (Chapter 5; DuBois 19811, indicatesthat Mugu Lagoon and other southernCalifornia estuarine systems usually opento the sea might be important to thestock. Therefore, the unusual characteristicsof the shovelnose guitarfish's useof the lagoon merit more study.This list of information gaps is indicativerather than exhaustive. The mostimportant function that this profile canser-ve is to provide the framework forefficiently fil ling those gaps and othersthat become evident later.

REFERENCESAdams, S.M., and J.W. Angelovic, 1970.Assiinilation of detritus and its associatedbacteria by three species ofestuarine animals. Chesapeake Sci. 10:249-255.Allen, L.G. 1976. Abundance, diversity,seasonality and co~nmuni ty structure ofthe fish populations of Newport Bay,California. M,A, Thesis. CaliforniaState University, Ful lerton.Bascorn, W. 1980. Waves and beaches: thedynamics of the ocean surface. AnchorPress, Garden City, N.Y,Baxter, J.L. 1974. Inshore fishes ofCal i forni a, Cal i fornia Department ofFish and Game, Sacramento.Biddle, K.T. 1976. Physical and biogenicsedimentary structures of a recentcoastal lagoon. M.A. Thesis. RiceUniversity, Houston, Tex.Allen, L.G. 1980. Structure and produc- Bradshaw, J., 5. Browning, K. Smith and J.tivity of the littoral fish assemblage Speth. 1976. The natural resources ofof Upper Newport Bay, Gal iforniae PheD* Agua Hedionda Lagoon. Coastal WetlandDissertation. University Southern Cali- Series no. 16. California Departmentfornia, Los Angcies. Fish and Game, U.S. Fish and WildlifeService,Andre, J.E., and H.W. Anderson. 1961, Variationof soil ero~ibi,i ty ,,,it.,California Department of Food and Agriculgeographiczone, elevation, and vegetationtype in northern California wildture.1978. Report on environmentalasses~ment of pesticide regulatory pro-1 ands. J. Geophys. Res. 66:3351-3358. grams.Draft.Ven tura County, Sacramento.fitwood, J .I-. , and D.W. I4insky. 1983. Least California State Coastal Conservancy.tern foraging ecology at three major 1982. Los Cerritos wetlands: alterna-Cal i fornia breeding colonies. Western tive wet1 and restoration plans report.Birds 14:57-72. Oak1 and, Ca1 i f.Baker, R.~. 1976. ecologicalstudy ofCalifornia Water Resources Control Board.parasitism in estuarine fishes. Ph.D. 1979. Water quality monitoring reportDissertation. University of California, No. 79-5, Mugu Lagoon to Latigo Point.Santa Barbara.Sacramento.Baldwin, J.L. 1974. Climates of the UnitedStates. National Oceanic and AtmosphericAdministration, Washington, D.C.Barry, J.P., and G.M. Cailliet. 1981, Theutilization of shallow marsh habitats bycoramercial ly important fishes in El khornSlough, California, Pages 38-47 in D.Koch, ed. Cal -Neva W i 1 dl i fe ~raxactions.Carpel an, L.H. 1969, Physical characteristicsof southern California coastallagoons. Pages 319-334 2 A.A.CastaEares and F.B. Phfeger, eds. Lagunascosteras, un simposia. UniversidadNacional Autonorna de Mexico.Chapman, J.W., C.P, Onuf, and M.L.Quammen. 1982. Effects of fish predationon peracarid crustaceans in MuguLagoon, Cal i fornia. Pages 274-285 &

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L R.eigl.nt's rlucrrr.lon No.f he Ecology of Mugu h3o~n, Cal ifornia : An Estuarine Profile$4. ewer€ antsJune 1987d.Christopher P.OnufAuthor's Affiliation:Marine Science InstituteUniversity of CaliforniaSanta Barbara, CA 93106ra hiactR.+(rmorr writ NO.11- Daa-(C) or Ib*nt(e) NO.02)12. Xpomonna Osy.nt+.Ploa Mdra~National Netlands Research CenterResearch and DevelopmentU.S. Fish and Wildlife ServiceWashington, OC 20240ra- rror or ~.a* s, -Id amaeQdMugu Lagoon is significant as one of the least dfstgrbed and best protected estuariesin southern Calffarnia; thus, this small estuasfne system can serve as a baseline modelfor the region. This report samarrizes and synthesizes scientific data on the ecologicalstructure and functioning of the estuary, includ+ng djscussions of cltmate, hydrology,geology, physiog~apby, btatic assmblages, and ecological processes and interactions.The estuary exhtbtts e~trme~uariability +n freshwater inputs, being at times totd'llymarfne and at ather times flubbed by stomwater cunoff frm the watershed. Major stonnsin I978 and 1980 resulted dn sedimentatton that drastically altered benthic cornmartitiesand resulted in changes in the< distribclf ion of submerged aquatic vegetation and benthos,and fish and shorebird use .of' bhese food resources.Mugu Lagoon is psrt of a nasal base and the~efore not subject to the development pressuresfacing many other southern Cali fornja estuaries. Storm-produced sedtmenttthonremains a management concern, as wll as closure of the mouth of the lagoon due &olittoral drift of sand along Dhe barrier spit.Estuaries, ecology, geology, hydrology, climate, nekton, a1 gae,biological productivityb. Ideritlfi~~/OWn-Endcd T~~~~wetlands, energy flow, nutrient cycl ing, emergent vascular plantsc COSATI FieldlGroupAgsrlrbsilty StatementUnl ini ted distributjonU S GWERNMEMPRIKT1NGOFFICE 1987-761-070 40014(Fcrmerly lfF1.S-35)~epsemwd at commm*