The Ecology of the Seagrasses of South Florida - USGS National ...

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Chemical Changes During Decomposition The two general processes that occur during decomposition, loss of plant compounds and synthesis of microbial biomass, can be incorporated into a generalized model of chemical changes. Initially, the leaves of turtle grass, manatee grass, and shoal grass contain 9% to 22% protein, 6% to 31% soluble carbohydrates, and 25% to 44% ash (dry weight basis), depending on species and season (Dawes and Lawrence 1980). Direct assays of crude fiber by Vicente et al. (1978) yielded values of 59% for turtle grass leaves; Dawes and Lawrence (1980) classified this material as "insoluble carbohydrates" and calculated values of 34% to 41% for this species by difference. Initially, losses through translocation and leaching will lead to a decrease in certain components. Thus, the organic carbon and nitrogen content will be decreased, and the remaining r~aterial will consist primarily of the highly refractive cell wall compounds (cell ulose, hemicell ulose, and 1 ignin) and ash (Harrison and Mann 1975b; Thayer et al. 1977). As microbial degradation progresses, the nitrogen content will increase through two processes: oxidation of the remaining ni trogen-poor seagrass compounds and synthesis of protein-rich microbial cells (typically 30% to 50% protein) (Thayer et al. 1977; Knauer and Ayers 1977). The accuslulation of microbial debris, such as the chi tin-containing hyphal walls of funci, may also contribute to the increased nitrogen content (Suberkropp et al. 1976; Thayer et al. 1977). Nitrogen for this process is provided by adsorption of inorganic and organic nitrogen from the surrounding medium, and fixation of atmospheric W,. For tropical seagrasses, in particular, there is an increase in ash content during decomposition because of deposition of carbonates during microbial respiration and growth of encrusting algal species, and organic carbon usually continues to decrease (Harrison and iSann 1975a; Knauer and Ayers 1977; Tkayer et 31. 1977). -- Chemical Changes as Indicators of Food Val uc Nitrogen content has long been considered a good indicator of the food value of detritus and has been assumed to represent protein content (Odum and de la Cruz 1967). Subsequent analyses of detritus from many vascular plant species, however, have shown that up to 30% of the nitrocen is not in the protein fraction (Harrison and Mann lS75b; Suberkropp et al. 1976; Odum et a1 . 1979). As decomposition progresses, the non-protein nitrogen fraction as a proportion of the total nitrogen can increase as the result of several processes: complexing of proteins in the lignin fraction (Suberkropp et a7. 1976) ; production of chitin, a major cell wall compound of fungi (Odum et al. 1979b); and decomposition of bacterial exudates (Lee et al. 1980). As a result, actual protein content may be a better indicator of food value. Thayer et a1 . (1977) found that the protein content of Zostera 1 eaves increased from standing dead to detrital fractions, presumably due to microbial enrichment. The role of the non-protein and protein nitrogen compounds in detri tivore nutrition is not presently well understood. Like many higher plants, tropical seagrasses contain phenol ic acids known as a1 1 el ochemical s. These compounds are known to deter herbivory in many plant groups (Feeny 1976). Six phenolic acids have been detected in the leaves, roots, and rhizomes of turtle grass, manatee grass, and shoal grass (Zapata and WcKillan 1979). In laboratory studies two of these compounds, ferulic acid and p-couwaric acid, when present at concentrations found in fresh leaves, inhibited the feeding activities of detritivorous amphipods and snails grazing on 2. alterniflora detritus. During decomposi ton the concentrations of these compounds decreased to levels that did not significantly inhibit the feeding activities of the animals (Val iela et a1 . 1979). Seagrass leaves nay also contain compounds that inhibit the growth of microorganisms; this in turn would decrease the usahta nutritfena? value cf the detritus. Water soluble extracts of fresh or recently detached 1. marina 1 eaves inhi hi ted the orowth of diatoms, phytoflauel lates, and bacteria (Harrison and Chan 1980). The inhibitory compounds are not found in older detrital leaves or ones that have been partially desiccated.
Re1 ease of Dissolved Organic Matter carbon than did the particulate carbon fraction (Robertson et a1 . 1982). Seagrasses re1 ease subs tanti a1 DOC may a1 so become available to conamounts of dissolved organic carbon (DOC) sumers through incorporation into particuduring growth and decomposition. The DOC late agaregates* Microorganisms attached fraction is the most readily used fraction to particles wilt assimilate DOC from the of the seagrass organic matter for micro- water column, incorporating it into their organisms and contains much of the so1 uhf e cells or secreting it into the extracellucarbohydrates and proteins of the plants. lar materials associated with the parti- X t is quickly assimilated by microorgan- cles (Paerl 1974, 1975). This rnicrohial ly ism, and is available to consumers as mediated mechanism also makes seagrass DOC food In sfgnl ficant quanti tles only after available for consumers. this conversion to microbial biomass. Thus, the utilization of seagrass DOC is In most marine systems the DOC pool functionally similar to detrital food webs contains 100 times more carbon than the based on the particulate fraction of sea- particulate organic carbon pool (Parsons grass carbon. Both epiphytes and leaves et al. 1977; references therein). The of Zostera are capable of taking up label- cycl ing of DOC and its utilization in deledTg8c compounds (Smith and Penhale trital food webs are complex. The highly 19130). labile nature of seagrass DOC sugaests that it may play a significant role in Experlrnents designed to quantify the supporting secondary productivi ty. release of DOC From growing seagrasses have ylelded a wide range of values, The Role of the Oetrital Food Wet? short-tern re1 ease of recently synthesized photosyntkatc from blades of turtle grass The detrital food web theory reprewas found to be 2% to la%, usfng radio- sents our best understanding of how the labelled carbon (Wetzel and Penhaf e 1979; unajor portion of seagrass organic carbon Bryl insky 1977). Losses to the water col - contri hutes to secondary productivity. The umn frat!! the enttre community, including organic flatter of fresh seagrasses is not belawground bi onass and decomposing par- cornnonly util ized by many animals hocatrse ltons, may &e much higher. Kirkman and of various factors, including their low Reid (1979) found that 50% of the annual concentrations of readily available nitroloss af organic carbon from the Posidon& gen, high concentrations of fiber, and the - &@st- seagrass community w a r t h e presence of inhibitory compounds. The par- form of: DOC, ticulate and dissalved fractions of seagrass carbon scan to become potential food Relcarse of DOC from detri tar leaves for animals primarily after colonization may a1 so be substantial. In freshwater by fnicroorganisfils. During decomposition macmphytes, leachlng and autolysis of DOC the chemical nature of the detritus is lcad ts a rapid 50% loss of weight (Otsuki changed by two processes: loss of plant and Wetzel 1974). fn laboratory experi- conpounds and synthesis of microbial prornents dried turtle grass and manatee grass ducts. 1 eaves released 13% and 20X, respectively, of' thetr organfc carbon content during The deconpaser ciomuni ty also has the teaching under sterile candi tions (Robert- enzyrratic rnechanis~vs and abil f ty to assimson et at. 3.982). ilate nutrients from the surrounding medium, leading to the enrichment of the detritus as a food source. As a result, the The carbon released as DOC is ex- decomposer comm?rnity represents a readily tt*c:?,cly 12b.fle and ir; rapfdly assfjnj jdted t,'sdBle tropkic level Bett!cer, the producby microorganl"sms (Otsuki and It!et.rel 1974; ers and [nost animal consumers. In this Gry'iinsky 19771, which leads to its immed- food weh, the consumers derive nutrition iate availabil ity aas food for second at*^ largely fran Ltte nicrohial coa~ponents of eonsumerr. In 14-day lahoratot-y incuha.. the detritus. This decornposer co~~uni ty tions, the DOC released by turtle grass 1s inFluenced by crnviront~ental conditions and ~anatee qrass leaves supported 10 and biological interactions, including the Limes rnore ~nkrobial biomass per unj t feed~ng activities of cansur?ers. 74
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F WS/O&S-82/25 September 1882 Repri
Page 3 and 4:
1 DISCLAIMER The findings in this r
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CONTENTS (continued ) Page CHAPTER
Page 8 and 9:
TABLES Number Temperature, salinity
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CHAPTER 1 INTRODUCTION 1.1 SEAGRASS
Page 15 and 16:
Key Went St Pstarobur~ Cedor Key Pa
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(4) The ability to complete their s
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in disturbed areas, and in areas wh
Page 21 and 22:
AVERAGE LEAF WIDTH I DISTANCE BETWE
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grass, and shoal grass in various 1
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Sediment Elevation (c m) Leaf Densi
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indication of a 1 ini tation on pro
Page 29 and 30:
CHAPTER 3 PRODUCTION ECOLOGY The de
Page 31 and 32: 1 isl;s conpdratiue Piorrlass value
Page 34 and 35: Net production measurements for ~10
Page 36 and 37: of seagrasses was bicarbonate ion,
Page 38: Currently the main 1 imitations of
Page 42 and 43: CHAPTER 4 THE SEAGRASS SYSTEN 4.1 F
Page 44 and 45: Figure 9. B1 owout disturbance and
Page 46 and 47: Keys waters. Where the continental
Page 48: 4.5 STRUCTURAL AND PROCESS SUCCESSI
Page 51: theft- h~ldfas t. Prirqary strbstrd
Page 54 and 55: Figure 15. Tha1 assia blades showin
Page 58 and 59: Fish I] lnver tebrates HEAVY THIN S
Page 61 and 62: Figure 19. Small grouper (Serranida
Page 63 and 64: 81 though crocodiles undoubted1 y f
Page 66 and 67: CHAPTER 6 TROPHIC RELATIONSHIPS IN
Page 68: I\iumcrous fishes ingest sor:e plan
Page 73 and 74: Table 1C. Continued. tlerbi vore Pa
Page 76 and 77: The herbivory of parrotfish and sea
Page 78 and 79: 1 eaves pl us their epiphytes avera
Page 80 and 81: the rate of biological breakdown of
Page 84: CHAPTER 7 INTERFACES WITH OTHER SYS
Page 87 and 88: Use of adjacent grass and sand flat
Page 89 and 90: etained in the bed to contribute to
Page 91 and 92: 1972). Sinilar habitat use by juven
Page 93 and 94: CHAPTER 8 HUMAN IMPACTS AND APPLIED
Page 95 and 96: Taylor and Sa1 oqan (1968) contrast
Page 97 and 98: on the &ach (Radeau and Rerquisrt.
Page 99 and 100: the closed systerq, however. Thorha
Page 101 and 102: 1981. The pit was created over 30 y
Page 103 and 104: with over 70% of gulf recreational
Page 105 and 106: ~bb~tt, #.P,, 3.C. Ogden, and 1.A.
Page 107 and 108: higher consumers in a seagrass com-
Page 109 and 110: shrimps (3ecapoda: Palaelqonidae).
Page 111 and 112: Ehrl ich, P.R., and A.H. Ehrl ich.
Page 113 and 114: Caribb. Res, Inst. t8ater Pollaat.
Page 116 and 117: crustaceans. Rec. Oceanogr. Uks., i
Page 118 and 119: tlayer, A.G. 1918. Toxic effects du
Page 120 and 121: Apalachicol a Bay, Florida US4. Gio
Page 122 and 123: antillarum Phil ippi : Formation of
Page 124 and 125: Prachaska, F. J., and 9.C. Cato. 19
Page 126 and 127: Sims, H.W., Jr., and R.M. Ingle. 19
Page 128 and 129: of know1 edge and research needs. P
Page 131 and 132: Wood, E.J.F., and J.C. Zieman. 1969
Page 133 and 134:
APPEMDI X KEY TO FISH SUPVEYS IN S0
Page 135 and 136:
L n 'u m (U m 'r .r > FVIL (U > El-
Page 137 and 138:
"l .^ -00 "l Q W O Z& n 0 "l m c 0,
Page 140:
... m h LI L Cn dC 3 Yu O 0 0 ox .-
Page 144 and 145:
List of fishes and their diets from
Page 146:
List of gishes and their diets from
Page 149 and 150:
LO) L O)= a, Oi D L & WOC C .- s g'
Page 152:
--C) h W wcn Old
Page 155 and 156:
C C +m" CX r .-- a * 'PI C7 C T 4 b
Page 160:
-. "-1 --- --- -- - ---- -- - - - .
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