The ecology of eelgrass meadows of the Atlantic coast

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stand provides a continuous cover of vegetation throughout most of the year. 1.3 EELGRASS "WASTING DISEASE" The observations of Petersen (1891) and Ostenfeld (1905) initiated a period of relatively i ntense ecological surveys on eelgrass in Europe, particularly in Danish waters. In 1918, Petersen summarized the bulk of the Danish work and synthesized a trophic model of the Kattegat region of Denmark based almost exclusively on the production of eelgrass (1 i ttle scientific information was available at that time on phytoplankton production). His model, which postulated that cod and plaice were dependent on the eelgrass community for food resources, was put to the test in the 1930's during and following a natural catastrophy to eel grass populations along most of the Atlantic coast. Even with the publication of the hypothesis of Petersen, very little research on the ecology of seagrasses was carried out in North America prior to about 1940. Only after the nearly catastrophic decline in eelgrass stocks over most of its range along the Atlantic Ocean in Europe and North America in 1931 and 1932 did eelgrass systems again became a focus of research. Tutin (1942) reported that between 1930 and 1933 the "wasting diseasett, as it has been termed, had resulted in the destruction of 90% of all eelgrass throughout its range in the Atlantic. Perhaps no one natural event has centered so much attention on a marine ecosystem type. The demise of eelgrass resulted in an upsurge in scientific research in both North America and Europe that centered on diagnostic evaluations of changes in the plant and on attempts to trace down its cause. Much of the research was natural history observations and generally lacked quantitative information. These observations, together with studies on the decl i ne of associated faunal populations, particularly those related to fisheries, provoked emotional responses that may even be heard today. The cause of the massive decline remains unresolved. Initially Laoyri nthu i a macrocyst i s was suspected as the causitive agent since it was found associated with dying eelgrass blades (Renn 1934 and many others). This organism originally was considered a slime mold but is now listed in the phylum Gymnomyxia, subphylum Labyrinthulina (Lindsay 1975). Labyrinthula is a saprophyte that apparently penetrates eelgrass leaves only as the leaves become moribund (Porter 1967). Further, Labyrinthula is found commonly associated with heal thy stocks of eelgrass (Young 1938; Porter 1967; Phi 11 ips 1972). Bacteria, fungi, commercial harvesting of fishery organisms, pollution, and competing species have been imp1 icated as possible causitive agents in the decline, but they have never been conclusively shown to have contributed to the 'wasting di sease" event. More recently, Rasmussen (1973, 1977) presented evidence that the detline in Denmark (and possibly elsewhere) was associated with a period of warm summers and exceptionally mild winters. Whatever the cause, there is little doubt that the massive decline of eelgrass hadt both geomorphol ogical and biological consequences. Rasmussen (1973, 1977) discussed both aspects in detail. The most obvious effects were those associated with sedimentary and current regimes. After an eel grass meadow di sappeared, the substrate became coarser, depending on the prevai 1 i ng current regime, and long, permanent sandbars built up. Sandy beaches that once had been protected by eelgrass became rocky slopes (Figure 9). In addi- Figure 9. Typical subtidal-jntertidal zonation before (upper) and after the depletion of eelgrass from Danish fjords. (Redrawn from Rasmussen 1973.)
tjon, deposits of fine muds, which were adjacent to the eelgrass beds, changed from low oxygen, sulfidic oozes to OX i di zed sediments. Sediments that had been domi nated by burrowi ng, depositfeeding invertebrates became dominated by encrusting or fouling, filter-feeding species when there was no longer protection provided by eel grass meadows. Similar changes may have occurred in North America. Stauffer (1937, p. 429- 430) stated, "The disappearance of the mat of vegetation permitted increased scouring and hence changes in composition of the sediments. .. . Indirectly, the disappearance of the plant may have caused changes in the water circulation in the lagoon, changes in the amount of dissolved oxygen, in temperature, and in pH. The re1 at ive importance of the physi cochemi cal changes compared to the biotic changes remains to be investigated.. ." The role of eel grass and seagrasses in general in modi fyi ng sediment and current patterns, however, received 1 i ttle further attention until the 1970's. Along with substrate modifications that resulted from the loss of the seagrass meadow came changes in the faunal community. Near Woods Hole, Massachusetts, Stauffer (1937) noted that species living on or among the grass bF ades di sap peared and that overall species abundance decreased. Similar changes were not reported to have occurred in Denmark (Rasmussen 1973, 1977). The majority of literature on fauna uti 1 ization of eel grass meadows before the catastrophy is qualitative, but there is consensus among the scientific communit~ that f i sheries did change, a1 though slowly at first (Thayer et al. 1975b; Zieman 1982). Whether this change was the result of a loss of food resources (e.g. fauna, epiphytes, and detritus) or refuge is unknown, and present research efforts are attempting to unravel the many roles the System plays. Commercial fisheries did not decline to the degree predicted by Petersen's (1918) calculations, yet Milne and Milne (1951, p. 53) stated, perhaps Somewhat emotionally, that the eelgrass catastrophe (which they equated with the Black Death of the 1300's) undoubtedly caused a major decline in fisheries popul ations--"Fi shermen found that the abundance of cod, she1 lf ish, scal lops, crabs, and sea staples fell sharply." Dexter (1947) further reported that lobsters, eels, and mud crabs also declined in abundance. In general , however, decl i nes i n abundance of species important to major recreational and/or commerci a1 fisheries, if they occurred, could not be recognized quantitatively, except for a few species. For example, Patriquin and Butler (1976) reported that residents of the Kouchi bouquac region of New Brunswick, Canada, observed no major differences in fisheries between the periods of eelgrass presence and absence. Even though Petersen's calculations predicting large declines in fisheries did not materialize for most recreational and commercial populations (at least within the detection capabi 1 i ties of recreational and comercia1 harvest statistics of that time), two notable exceptions (one for waterfowl and one for a fisheries species) have been documented. One was the catastrophic decline of the Atlantic brant (Branta ber- -- nicla hrota), that fed at the timelmost exclusively on eelgrass, and the more limited decline of the Canada goose, 6. canadensis (Cottam 1934; Cottam et aT. 1944; Cottam and Munro !954; den Hartog 1977). The brant pcpulation almost disappeared following the decline of eelgrass. The decline in numbers a1 so coincided with a period of poor reproductive success which may have contributed to reduced populations (Palmer 1976). The brant population did not recover unti 1 the early 19501s, after which the brant's dietary preference shifted to widgeon grass and sea lettuce, Ulva lactuca. With the reappearance of eel grass, however, there has not been a concommitant return to an almost exclusive eel grass diet. Catastrophic population decl ines also were documented for the bay scallop, Argopecten irradi ans, following the decline of eelarass. The scallop depends on seaqrass blides for attachment of the post1 a&ae (Gutsel 1 1930; Thayer and Stuart 1974; Fonseca et al. in press). The Say scallop can use detritus derived from the decay of eelgrass leaves (Kirby-Srni th 1972; Kirby-Smith and Barber 1974), obtaining up to 30% of its body
Page 1 and 2: FWSlO BS-84102 July 1984 The Ecolog
Page 3 and 4: The findings in this report are not
Page 5 and 6: PREFACE ...........................
Page 7 and 8: FIGURES Page 1 Major geographic dis
Page 9 and 10: Number 3 9 40a Page Computer simula
Page 11 and 12: TABLES Number Page la lb Weight and
Page 13 and 14: ACKNOWLEDGMENTS The development of
Page 16 and 17: CHAPTER 1 INTRODUCTION 1.1 TAXONOMI
Page 18 and 19: mechanical support and absorptive t
Page 20 and 21: insolation and water clarity, is a
Page 24 and 25: carbon from detritus (Thayer et al.
Page 26 and 27: from interstitial water in the sedi
Page 28 and 29: oldest standing leaf meristem withi
Page 30 and 31: speci a1 i zation in eelgrass. Rece
Page 32 and 33: acd female flowers mature coinciden
Page 34 and 35: viability 7s iess than cerldin. Fie
Page 36 and 37: Popuiarion Gro~th As part of this e
Page 38 and 39: - Table 2. Instantaneous coefficien
Page 40 and 41: are pnotosynthetical lj important.
Page 42 and 43: JANUARY 29. 1980 LIGHT LEVEL (Percm
Page 44 and 45: coast locations and one Pacific coa
Page 46 and 47: Vp-7 --A f p4 q,7 LIIyI ,,, I y Y ~
Page 48 and 49: Table 3. (continued) Table 3. (conc
Page 50 and 51: iomass is lost rapidly. It is repla
Page 52 and 53: yield approiinately 50-182 g C yr-l
Page 54 and 55: Figure 24. Three-dimensional il lus
Page 56 and 57: U, cm/sec Figure 26. Velocity profi
Page 58 and 59: strcct2ri ng eelgracc meadows. The
Page 60 and 61: a? lochthonous material tra~ped by
Page 62 and 63: PERCENT ORGANIC MATTER (dry wt. bas
Page 64 and 65: WATER COLUMN -------- FLOCCULENT IN
Page 66 and 67: WATER COLUMN - SORBED FLOCCULENT PH
Page 68 and 69: phytoplankton and release DOM and i
Page 70 and 71: 3.4 A SCENARIO OF EELGRASS MEADOW o
Page 72 and 73:
Sedimentat~on /-f\ in bed J Prolife
Page 74 and 75:
Figure 40. (a) Wavelets refracting
Page 76 and 77:
that future studies be directed to
Page 78 and 79:
system is dominated by the plant co
Page 80 and 81:
eel grass leaf itself, and .its aen
Page 82 and 83:
in the e~';hytk conascity ;n of eei
Page 84 and 85:
observed a similar trend in one mea
Page 86 and 87:
Table 6. Partial list of epibenthic
Page 88 and 89:
elate to swarming behavior of the z
Page 90 and 91:
supply (Thayer et al. 1979). Seagra
Page 92 and 93:
ecorded as permanent residents of e
Page 94 and 95:
Table 10. !concluded) . Species nam
Page 96 and 97:
% sandbar shark (Carcharhinus umbeu
Page 98 and 99:
of their seasonally 1 arge numbers
Page 100 and 101:
when algal cover becomes sparse. Pr
Page 102 and 103:
(i.e., nearness to sources of terre
Page 104 and 105:
Table 13. Organi sms that reportedl
Page 106 and 107:
Tab1 e 13, (concl uded) . Herbi vor
Page 108 and 109:
not consider phytoplankton. Stable
Page 110 and 111:
-----------____ -. '. ---* '. . . .
Page 112 and 113:
Microbial Colonization and Activiti
Page 114 and 115:
allel ochemi cal s. These compounds
Page 116 and 117:
CHAPTER 5 INTERSYSTEM COUPLING Tida
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(Zieman et al. 1979). This export f
Page 120 and 121:
July wu8t I 1976 1977 Figure 55. Wr
Page 122 and 123:
Table 15. General sequence of event
Page 124 and 125:
CHAPTER 6 CONSIDERATIONS FOR MANAGE
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or from drift off the immedi ate im
Page 128 and 129:
-- Bittium varium (Figure 42) may h
Page 130 and 131:
in productivity have potential for
Page 132 and 133:
covered with seawater for transport
Page 134 and 135:
Table 16, Estimates of the average
Page 136 and 137:
japonica and Kuppia maritima, at Ro
Page 138 and 139:
Crosby, N.D., and R.G.B. Reid. 1971
Page 140 and 141:
Fonseca, M.S., J.J. Fisher, J.C. Zi
Page 142 and 143:
in vegetated aquatic habitats. J. E
Page 144 and 145:
Kirkman, H., and P.C. Young. 1981.
Page 146 and 147:
Roy, eds. Handbook of seagrass biol
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Orth, R.J. 1975. Destruction of eel
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Pomeroy, L.R., and D. Deibel. 1980.
Page 152 and 153:
Smith, G.W., A.M. Kozucki, and S.S.
Page 154 and 155:
Tubbs, C.R., and J.M. Tubbs. 1982,
Page 156 and 157:
systems. Ann Arbor Press, Ann Arbor
Page 158 and 159:
Masti ocoleus testarum h y n g b y
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-- S. ulna - S. undlildta iabell ar
Page 162 and 163:
Microdeuto~us . - - - - -~~ darnnon
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The ecology of eelgrass meadows of the Atlantic coast

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