The Ecology of Tijuana Estuary, California: An Estuarine Profile

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Table 4. Percent occurrence of the more abundant species in the transition from upland to wetland at the northernmost part of Tijuana Estuary. Data are from 0.25 rn2 circutar quadrats (numbers sampled in parentheses) taken per 40-cm elevation class (Zedler unpubl. data). Elevation classa 1 2 3 4 5 6 7 8 9 10 11 Species (29) (99) (52) (25) (33) (30) (31) (34) (22) (33) (8) Artemisia californica Eriogonum fascicula tum Haplopappus venetus Rhus laurina A triplex semibacca ta Cressa truxillensis Dis tichlis spicata Frankenia grandifolia Lycium californicum Monanthochloe littoralis Salicornia subterminalis Salicornia virginica Limonium californicum Atriplex watsonii aElevation classes each included a 40-crn (16-inch) elevat~on range, they are numbered from low to h~gh elevation at the uppermost elevations and the taller cordgrass (Sparl~na folrosa) at the lowest elevations helps to designate higher and lower marsh habitats. Unlike the drought-deciduous coastal scrub species, the plants of the salt marsh grow through the summer and early fall. Presumably, th~s is because the wetland plants have access to moisture from tidal waters throughout the dry summer and fail Figure 1 8. The wandering skipper. Body 14 mm long. Nlclntire collection, copyright 1986 by Zedler. The hlgher salt marsh (F~gure 20) is one of the most complex wetland communities, because it is subject to aiternating envi:onmental extremes of drought and inundation, because d~sturbance is frequent, and because its topography is sometimes mounded. Eighty-six mounds that ranged from 9 to 57 cm in helght and 5.6 to 18.6 m rn diameter were characterized in 1984 (Cox and Zedler, in press)
Each "island" of higher topography allows species diverse; the larger the mound, the longer the plant of the higher marsh to extend farther into the species list. In addition, the mounds provide wetland. The marsh periphery is thus patchy and habitat for several herbivorous mammals that in turn influence mound and Intermound vegetation. Cox attributes the mound formation to ground squirrels and other burrowing mammals that utilize the high ground. He suggests that over centuries, they gradually transport so~ls toward a central burrow opening until a pattern of mounds and intermound areas is created. Whether the concentration of squirrels on mounds is cause or effect, however, is hard to demonstrate in shortterm studies. What is clear is that the mounds of high ground, which are surrounded by wetter marsh, add small-scale hab~tat diversity to the wetland. Where adjacent areas have been filled or developed, these islands provide the only clue to the higher-elevation communities that might have occurred rn the transition zone. The invasion process can be seen in wet winters, such as 1983, when high spots are leached of their salts and upland weeds (e.g., the wild radish, Raphanus sativum) germinate and grow. Such salt-intolerant species rarely persist beyond the next dry season. Herpetofauna are l~kewise lim~ted to these areas of high ground. The San Diego horned lizard (Phrynosoma coronatum blainv~llei; Figure 21) is declining because of frequent collection, but a few remain in isolated areas. Snakes are not common, and their rarity partly explalns the abundance of rodents such as ground squirrels (Spermoph~lus beechyid and rabbits (Lepus californicus and Sylv~lagus audubonil sactidregil that populate the upper marsh Birds that nest in the high marsh include the white-crowned sparrow (Zonotnchia leucophrys), song sparrow (Melospira melodia), western meadowlark (Sturnella neglecia), and killdeer (Charadnus vociferus). Other birds use the area extensively for foraging. Raptors, such as the northern harrier (Circus cyaneus), Amertcan kestrel 1 (Falco sparverius), and golden eagle (Aquila chrysaetos), explolt the populations of small mammals; while Belding's Savannah sparrows, horned larks (Eremophila alpestris), and loggerhead shrikes (Lanius ludovic~anus) feed on Expisnation of X axis insects and other small prey (A. White, SDSU, pers. Cla~r~ Elevation Quadrats Class Elevation Quadrats comm ,, numbef (cm MSL) in crass number (cm MSL) in class " -- - . 3 30-39 7 8 80-89 35 Gharacteristic plants of the higher marsh are 4 40-49 f 2 B 90-99 30 the perennial glasswort (Salrcornla subterm~nalts), 5 50-59 22 10 100-109 39 the shore grass (Mananthochloe Iittoral~s), alkali 6 60-69 113 11 110-130 8 7 70.79 95 heath, sea lavender, and Atr~plex watsoni~. Ail of these specles are perenn~als that reproduce Figure 1% The frequency of occurrence of abundant vegetatively, and seedlings are rare. Only dur~ng Plant species in the salt marsh of Tljuana Estuary (from the long ralny season of 1983 were there Zedter 1977). conspicuous episodes of seedling establishment 2 0
Page 1 and 2: June 1986 I THE ECOLOGY OF TIJUANA
Page 3 and 4: The findings in this report are not
Page 5 and 6: CONVERSION TABLE Metric to U.S. Cus
Page 7 and 8: Page 4.5 Energy Flow ..............
Page 9 and 10: Number Page The channel fish cornrn
Page 11 and 12: ACKNOWLEDGMENTS The California Sea
Page 13 and 14: Figure 1. Lacatlcrn of 71juana Estu
Page 15 and 16: Figure 3. Map6 of Tijuana Estuary s
Page 17 and 18: FI(I(uPc$ 4. Wei&rahOt@ patt@rns of
Page 19 and 20: also limitrng Hot, dry desert winds
Page 21 and 22: 2.3 LAND USE HlSPQWV Through exami!
Page 23 and 24: The nearby bridge remained, and ext
Page 25 and 26: flushing until mid-December 1984. E
Page 27 and 28: with seawater. Even in years with s
Page 29: flats ~n winter but not in midsumme
Page 33 and 34: The vegetation and soils of the upp
Page 35 and 36: populations (Massey 1979) The brrds
Page 37 and 38: c~n~entrations of insects, especial
Page 39 and 40: Frgufe 29. The Ifght-footed clapper
Page 41 and 42: Figure 30. During winter (above) th
Page 43 and 44: anlmal footprints, In the hardpan f
Page 45 and 46: Tijuana Estuary salt marsh Such exp
Page 47 and 48: Frgura 36 The etraracrel an& tidal
Page 49 and 50: ^_ _I __"___I _-a_. -- fable 7. Inv
Page 51 and 52: Pre- 1980 (excluding Hosrner Rehse
Page 53 and 54: Table 8. Average density (number/m2
Page 55 and 56: changes in envlronment has not been
Page 57 and 58: was dominated by goby species, Cali
Page 59 and 60: compared the ,chthyoplankton commun
Page 61 and 62: Figure 43, Birds of the intertidal
Page 63 and 64: -" and that the community was compo
Page 65 and 66: Willet (1 73) i - Water Depth (cm)
Page 67 and 68: Table 14. Early information on dune
Page 69 and 70: Figure 48. Birds that nest on the s
Page 71 and 72: CHAPTER 4 ECOSYSTEM FldNCTlONlNG St
Page 73 and 74: were no? irght-saturated untri expo
Page 75 and 76: Table 17. Conceptual model of chann
Page 77 and 78: Table 19. Net aboveground productiv
Page 79 and 80: _I___ I__-~--- 4.4.1 Nitragen Fluxe
Page 81 and 82:
i i t 1 1 I Table 22. Standing crop
Page 83 and 84:
calculated from chlorophyll a measu
Page 85 and 86:
Dissolved Organic Biomass Carbon De
Page 87 and 88:
CHAPTER 5 THE ROLE OF DISTURBANCES
Page 89 and 90:
Table 25. Changes in elevation in t
Page 91 and 92:
Table 26. Change in pickleweed cano
Page 93 and 94:
Table 27. Occurrence (in circular 0
Page 95 and 96:
perennials can survive long periods
Page 97 and 98:
An experiment was designed to deter
Page 99 and 100:
CHAPTER 6 MANAGEMENT CONSIDERATIONS
Page 101 and 102:
Closely associated with the researc
Page 103 and 104:
c. Dredging at Tijuana Estuary will
Page 105 and 106:
Table 30. Predicted impacts of redu
Page 107 and 108:
footed clapper rails; the picklewee
Page 109 and 110:
overwashas, and slabiiizatran rs rl
Page 112 and 113:
REFERENCES Allen, L.G. 1980. Struct
Page 114 and 115:
Minsky, D. 1984. California least t
Page 116:
30272 -101 REPORT WUMENTATION 1. RE
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The Ecology of Tijuana Estuary, California: An Estuarine Profile

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