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1.
The spatial arrangement of seagrass beds varies from scales of centimeters to meters (rhizomes, shoot groups), meters to tens of meters (patches), to tens of meters to kilometers (seagrass landscapes). In this study we examine the role of patch scale (patch size, seagrass % cover, seagrass biomass), landscape scale (fractal geometry, patch isolation) and wave exposure (mean wind velocity and exceedance) variables in influencing benthic community composition in seagrass beds at three intertidal sites in northern New Zealand (two sites in Manukau Harbour and one site in Whangapoua Harbour). Analysis of univariate community measures (numbers of individuals and species, species richness, diversity and evenness) and multivariate analyses indicated that there were significant differences in community composition inside and outside of seagrass patches at each of the three sites. Partialling out the spatial and temporal components of the ecological variation indicated that seagrass patch variables explained only 3–4% of the patch scale variation in benthic community composition at each of the sites. The temporal component was more important, explaining 12–14% of the variation. The unexplained variation was high (about 75%) at all three sites, indicating that other factors were influencing variation in community composition at the scale of the patches, or that there was a large amount of stochastic variation. Landscape and wave exposure variables explained 62.5% of the variation in the species abundance data, and the unexplained variation at the landscape level was correspondingly low (12%). Canonical correspondence analysis produced an ordination that suggests that, while mean wind velocity and exceedance were important in explaining the differences between the communities in the two harbours, spatial patterning of the habitat, primarily fractal dimension, and secondarily patch isolation (or some factors that were similarly correlated), were important in contributing to variability in community composition at the two sites in Manukau Harbour. This study suggests that spatial patterning of seagrass habitat at landscape scales, independent of the patch scale characteristics of the seagrass beds, can affect benthic community composition. Community composition inside and outside seagrass habitats involves responses to seagrass bed structure at a series of hierarchical levels, and we need to consider more than one spatial scale if we are to understand community dynamics in seagrass habitats.  相似文献   

2.
We sampled epiphytic and benthic macriinvertebrates in 20 beds of submersed vegetation throughout the Hudson River estuary to assess the importance of plant beds in providing habitat for macroinvertebrates and to determine which characteristics of plant beds affected the density and composition of macroinvertebrates. Macroinvertebrate densities in plant beds were 4–5 times higher, on average, than densities in unvegetated sediments in the Hudson. The macroinvertebrate community in plant beds was dominated by chironomid midges, oligochaete worms, hydroids, gastropods, and amphipods. Many species of macroinvertebrates were found chiefly on submersed plants, showing that plant beds are important in supporting biodiversity in the Hudson. Macroinvertebrates were most numerous in beds with high plant biomass and in the interiors of beds, whereas neither bed size nor position along the length of the estuary affected macroinvertebrate density. Community composition varied strongly with position along the river (freshwater versus brackish), habitat (epiphytic versus benthic), and position within the bed (edge versus interior). Plant biomass also influenced macroinvertebrate community composition, but bed area had relatively little influence.  相似文献   

3.
Three quarters of the global human population will live in coastal areas in the coming decades and will continue to develop these areas as population density increases. Anthropogenic stressors from this coastal development may lead to fragmented habitats, altered food webs, changes in sediment characteristics, and loss of near-shore vegetated habitats. Seagrass systems are important vegetated estuarine habitats that are vulnerable to anthropogenic stressors, but provide valuable ecosystem functions. Key to maintaining these habitats that filter water, stabilize sediments, and provide refuge to juvenile animals is an understanding of the impacts of local coastal development. To assess development impacts in seagrass communities, we surveyed 20 seagrass beds in lower Chesapeake Bay, VA. We sampled primary producers, consumers, water quality, and sediment characteristics in seagrass beds, and characterized development along the adjacent shoreline using land cover data. Overall, we could not detect effects of local coastal development on these seagrass communities. Seagrass biomass varied only between sites, and was positively correlated with sediment organic matter. Epiphytic algal biomass and epibiont (epifauna and epiphyte) community composition varied between western and eastern regions of the bay. But, neither eelgrass (Zostera marina) leaf nitrogen (a proxy for integrated nitrogen loading), crustacean grazer biomass, epifaunal predator abundance, nor fish and crab abundance differed significantly among sites or regions. Overall, factors operating on different scales appear to drive primary producers, seagrass-associated faunal communities, and sediment properties in these important submerged vegetated habitats in lower Chesapeake Bay.  相似文献   

4.
Structural equivalence between seagrass restoration sites and adjacent natural seagrass beds on the mid Texas coast was assessed six times between April 1995 and May 1997. Throw traps and corers were used for quantitative sampling. Restoration sites were 2.7 to 6.6 yr old when first sampled and 3.7 to 8.2 yr old when last sampled. There were few significant differences in water column, seagrass, or sediment characteristics, in fish and decapod (nekton) densities, or in nekton and benthos community compositions between restored and natural seagrass habitats at any time during the study period. Differences in densities of dominant benthic invertebrates were regularly observed, with greater densities of more taxa observed in natural seagrasses than in restored beds. Densities of Class Oligochaeta and the polychaetePrionospio heterobranchiata are proposed as potential indicators of structural equivalence in restored seagrasses. This study indicates that seagrass restorations in the vicinity of Corpus Christi, Texas, exhibit minimal quantitative differences in community structure (except for benthos) relative to adjacent natural seagrass beds after 3 to 5 yr.  相似文献   

5.
In nearshore ecosystems, habitats with emergent structure are often assumed to have higher ecosystem functioning than habitats lacking structure. However, such habitat-specific differences may depend on the surrounding environment. In this study, I examine the robustness of habitat-specific differences in ecosystem functioning for seagrass (Zostera marina) and adjacent bare soft sediments across varying environmental conditions on the Atlantic Coast of Nova Scotia, Canada, using secondary production as a metric. I also examine relationships of community secondary production and faunal structure with measured environmental variables (water depth, temperature, exposure, sediment, and plant properties). Benthic secondary production (invertebrates ≥500 μm) was higher in seagrass compared to bare sediments only at exposed sites with sandy sediments low in organic content, deep and cool water, and high belowground plant biomass. A regression relating community secondary production to the environmental variables explained 56% of the variance, while a constrained ordination explained 16% of the community structure. Important environmental determinants of community production were shoot density, temperature, depth, exposure, sediment organic content, and belowground plant biomass. Community structure was influenced by these variables plus sediment sand content and canopy height. This study shows that habitat-specific differences in secondary production may not be consistent across varying environmental conditions. Furthermore, seagrass beds are not always associated with higher ecosystem functioning than adjacent bare sediment. Both the surrounding environmental conditions and the presence of habitat structure should be considered for optimal management of nearshore ecosystems.  相似文献   

6.
Tidally driven flows, waves, and suspended sediment concentrations were monitored seasonally within a Zostera marina seagrass (eelgrass) meadow located in a shallow (1–2 m depth) coastal bay. Eelgrass meadows were found to reduce velocities approximately 60 % in the summer and 40 % in the winter compared to an adjacent unvegetated site. Additionally, the seagrass meadow served to dampen wave heights for all seasons except during winter when seagrass meadow development was at a minimum. Although wave heights were attenuated across the meadow, orbital motions caused by waves were able to effectively penetrate through the canopy, inducing wave-enhanced bottom shear stress (τ b ). Within the seagrass meadow, τ b was greater than the critical stress threshold (=0.04 Pa) necessary to induce sediment suspension 80–85 % of the sampling period in the winter and spring, but only 55 % of the time in the summer. At the unvegetated site, τ b was above the critical threshold greater than 90 % of the time across all seasons. During low seagrass coverage in the winter, near-bed turbulence levels were enhanced, likely caused by stem–wake interaction with the sparse canopy. Reduction in τ b within the seagrass meadow during the summer correlated to a 60 % reduction in suspended sediment concentrations but in winter, suspended sediment was enhanced compared to the unvegetated site. With minimal seagrass coverage, τ b and wave statistics were similar to unvegetated regions; however, during high seagrass coverage, sediment stabilization increased light availability for photosynthesis and created a positive feedback for seagrass growth.  相似文献   

7.
The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were investigated using a modified Nearshore Community Model (NearCoM). The model was enhanced to account for cohesive sediment erosion and deposition, sediment transport, combined wave and current shear stresses, and seagrass effects on drag. Expressions for seagrass drag as a function of seagrass shoot density and canopy height were derived from published flume studies of model vegetation. The predicted reduction of volume flux for steady flow through a bed agreed reasonably well with a separate flume study. Predicted wave attenuation qualitatively captured seasonal patterns observed in the field: wave attenuation peaked during the flowering season and decreased as shoot density and canopy height decreased. Model scenarios with idealized bathymetries demonstrated that, when wave orbital velocities and the seagrass canopy interact, increasing seagrass bed width in the direction of wave propagation results in higher wave attenuation, and increasing incoming wave height results in higher relative wave attenuation. The model also predicted lower skin friction, reduced erosion rates, and higher bottom sediment accumulation within and behind the bed. Reduced erosion rates within seagrass beds have been reported, but reductions in stress behind the bed require further studies for verification. Model results suggest that the mechanism of sediment trapping by seagrass beds is more complex than reduced erosion rates alone; it also requires suspended sediment sources outside of the bed and horizontal transport into the bed.  相似文献   

8.
Complex links between the top-down and bottom-up forces that structure communities can be disrupted by anthropogenic alterations of natural habitats. We used relative abundance and stable isotopes to examine changes in epifaunal food webs in seagrass (Thalassia testudinum) beds following 6 months of experimental nutrient addition at two sites in Florida Bay (USA) with different ambient fertility. At a eutrophic site, nutrient addition did not strongly affect food web structure, but at a nutrient-poor site, enrichment increased the abundances of crustacean epiphyte grazers, and the diets of these grazers became more varied. Benthic grazers did not change in abundance but shifted their diet away from green macroalgae + associated epiphytes and towards an opportunistic seagrass (Halodule wrightii) that occurred only in nutrient addition treatments. Benthic predators did not change in abundance, but their diets were more varied in enriched plots. Food chain length was short and unaffected by site or nutrient treatment, but increased food web complexity in enriched plots was suggested by increasingly mixed diets. Strong bottom-up modifications of food web structure in the nutrient-limited site and the limited top-down influences of grazers on seagrass epiphyte biomass suggest that, in this system, the bottom-up role of nutrient enrichment can have substantial impacts on community structure, trophic relationships, and, ultimately, the productivity values of the ecosystem.  相似文献   

9.
Seagrass beds provide important habitat for fishes and invertebrates in many regions around the world. Accordingly, changes in seagrass coverage may affect fish communities and/or populations, given that many species utilize these habitats during vulnerable early life history stages. In lower Chesapeake Bay, seagrass distribution has contracted appreciably over recent decades due to decreased water clarity and increased water temperature; however, effects of changing vegetated habitat on fish community structure have not been well documented. We compared fish community composition data collected at similar seagrass sites from 1976–1977 and 2009–2011 to investigate potential changes in species richness, community composition, and relative abundance within these habitats. While seagrass coverage at the specific study sites did not vary considerably between time periods, contemporary species richness was lower and multivariate analysis showed that assemblages differed between the two datasets. The majority of sampled species were common to both datasets but several species were exclusive to only one dataset. For some species, relative abundances were similar between the two datasets, while for others, there were notable differences without directional uniformity. Spot (Leiostomus xanthurus) and northern pipefish (Syngnathus fuscus) were considerably less abundant in the contemporary dataset, while dusky pipefish (Syngnathus floridae) was more abundant. Observed changes in community structure may be more attributable to higher overall bay water temperature in recent years and other anthropogenic influences than to changes in seagrass coverage at our study sites.  相似文献   

10.
Macroinvertebrates are a major food source for fish species and macrophyte beds are hypothesized to harbor a rich community of these organisms. Macroinvertebrates inhabiting the water column in two macrophyte beds and an adjacent open area were sampled in a small embayment of the tidal freshwater Potomac River. One macrophyte bed consisted of an almost complete monoculture ofHydrilla verticillata, while the second community was a more diverse mixture of plant species. In samples with substantial amounts of submersed aquatic vegetation (SAV), macroinvertebrate density was two orders of magnitude higher than and substantially more taxa were found than at the open water site. Total macroinvertebrate abundance was significantly greater at theH. verticillata site than at the mixed site in July, but no significant difference was observed in August. Taxa richness did not vary between the two vegetated sites in July but was higher in the mixed bed in August. While the two vegetated sites shared similar taxa, they differed in their abundance. TheH. verticillata site harbored more hydrobiid snails, and the mixed site was characterized by more chironomids and hydroptilid caddisflies. Differences between July and August collections were even greater than between sites. Numbers of hydroptilid caddisflies, baetid mayflies, and coenagrionid damselflies were substantially higher in August, while oligochaetes, hydrobiids, and chironomids were reduced. Results support the hypothesis that water-column macroinvertebrates are greatly enhanced in the presence of macrophytes. The ecological significance of the less substantial differences in macroinvertebrates between macrophyte beds requires further study.  相似文献   

11.
Functional trajectory models were used to assess the restoration of ecological functions in two transplanted eelgrass (Zostera marina L.) beds compared to three natural, reference beds in the Great Bay Estuary, New Hamsphire. Functional trajectory models describe the development of ecological functions over time in restored habitats relative to levels of function in natural habitats. We present the first application of trajectory models to transplanted seagrass and evaluate the utility of these models as a tool for assessing seagrass restoration. The project was an analysis of 9 yr of monitoring data, the longest monitoring of transplanted eelgrass to date. We used trajectory models to assess the time course of development of functions in transplanted beds by evaluating statistical trends, and to determine functional equivalence, defined as the time when functions in a transplanted bed reach an asymptote and are no more than 1 standard deviation below the reference mean. The functions modeled included primary production, 3-dimensional habitat structure, faunal use, and sediment filtering and trapping. Measured proxies for primary production and habitat structure increased logistically (sigmoidally) with time, reaching functional equivalence after 3 yr. In transplanted beds, trends in habitat use by infaunal invertebrates and fish were logarithmic, and values were functionally equivalent 2–4 yr after transplanting. We saw no trend in sediment filtering and trapping capacity of transplanted eelgrass over the 9 yr. Measures of function in both reference and transplanted beds fluctuated due to natural and anthropogenic disturbances. After reaching equivalence, measures of function in transplanted beds tracked those in reference beds, exhibiting long-term persistence and rebounding from disturbances similarly to reference beds. Trajectory models can illustrate the time course of eelgrass bed development, aiding the design of monitoring programs and the evaluation of ecological functional equivalence in seagrass restoration projects.  相似文献   

12.
We investigated the effects of differing spatial scales of seagrass habitat architecture on the composition and abundance of settling bivalves in a sub-tropical seagrass community. The density of newly settled bivalves was generally greater atThalassia testudinum grass bed edge (<1 m) compared to interior portions of the bed (>10 m). Deviation from this generalized pattern occurred when high densities of newly settled tulip mussels (Modiolus americanus) were recorded from the interior of the meadow, associated with aggregations of adult mussels. Bivalve settling densities appear to reflect settlement shadows of passively delivered larvae, bedload transport of newly settled individuals from unvegetated regions, as well as gregarious settlement among adult conspecifics. We also investigated the impact of seagrass patch shape and size on settlement by using artificial seagrass units (ASU) in separate short-term and long-term experiments. We found a positive relationship between ASU perimeter and bivalve abundance, suggesting that larval encounter rates with seagrass habitat may determine initial settlement patterns. Using ASUs we also investigated the relative role seagrass epiphytes play in determining the density of settling bivalves. Results showed greater settling densities where epiphytic secondary structure was elevated compared to controls, and bivalve density was significantly greater when ASUs were fouled with a natural community of epiphytes, suggesting that both microstructure and biofilms positively influenced bivalve settlement. We conclude that structural components of seagrass habitats increase bivalve settlement at multiple spatial scales, including epiphytic micro-structure, small-scale patch shape and size, and large-scale within habitat differences.  相似文献   

13.
Seasonal ichthyoplankton surveys were made in the lower Laguna Madre, Texas, to compare the relative utilization of various nursery habitats (shoal grass,Halodule wrightii; manatee grass,Syringodium filiforme; and unvegetated sand bottom) for both estuarine and offshore-spawned larvae. The species composition and abundance of fish larvae were determined for each habitat type at six locations in the bay. Pushnet ichthyoplankton sampling resulted in 296 total collections, yielding 107,463 fishes representing 55 species in 24 families. A broad spectrum of both the biotic and physical habitat parameters were examined to link the dispersion and distribution of both pre-settlement and postsettlement larvae to the utilization of shallow seagrass habitats. Sample sites were grouped by cluster analysis (Ward’s minimum variance method) according to the similarity of their fish assemblages and subsequently examined with a multiple discriminant function analysis to identify important environmental variables. Abiotic environmental factors were most influential in defining groups for samples dominated by early larvae, whereas measures of seagrass complexity defined groups dominated by older larvae and juveniles. Juvenile-stage individuals showed clear habitat preference, with the more shallowHalodule wrightii being the habitat of choice, whereas early larvae of most species were widely distributed over all habitats. As a result of the recent shift of dominance fromHalodule wrightii toSyringodium filiforme, overall reductions in the quality of nursery habitat for fishes in the lower Laguna Madre are projected.  相似文献   

14.
The fringing environments of lower Chesapeake Bay include sandy shoals, seagrass meadows, intertidal mud flats, and marshes. A characterization of a fringing ecosystem was conducted to provide initialization and calibration data for the development of a simulation model. The model simulates primary production and material exchange in the littoral zone of lower Chesapeake Bay. Carbon (C) and nitrogen (N) properties of water and sediments from sand, seagrass, intertidal silt-mud, and intertidal marsh habitats of the Goodwin Islands (located within the Chesapeake Bay National Estuarine Research Reserve in Virginia, CBNERR-VA) were determined seasonally. Spatial and temporal differences in sediment microalgal biomass among the habitats were assessed along with annual variations in the distribution and abundance ofZostera marina L. andSpartina alterniflora Loisel. Phytoplankton biomass displayed some seasonality related to riverine discharge, but sediment microalgal biomass did not vary spatially or seasonally. Macrophytes in both subtidal and intertidal habitats exhibited seasonal biomass patterns that were consistent with other Atlantic estuarine ecosystems. Marsh sediment organic carbon and inorganic nitrogen differed significantly from that of the sand, seagrass, and silt habitats. The only biogeochemical variable that exhibited seasonality was low marsh NH4 +. The subtidal sediments were consistent temporally in their carbon and nitrogen content despite seasonal changes in seagrass abundance. Eelgrass has a comparatively low C:N ratio and is a potential N sink for the ecosystem. Changes in the composition or size of the vegetated habitats could have a dramatic influence over resource partitioning within the ecosystem. A spatial database (or geographic information system, GIS) of the Goodwin Islands site has been initiated to track long-term spatial habitat features and integrate model output and field data. This ecosystem characterization was conducted as part of efforts to link field data, geographic information, and the dynamic simulation of multiple habitats. The goal of these efforts is to examine ecological structure, function, and change in fringing environments of lower Chesapeake Bay.  相似文献   

15.
Blue carbon initiatives require accurate monitoring of carbon stocks. We examined sources of variability in seagrass organic carbon (Corg) stocks, contrasting spatial with short temporal scales. Seagrass morphology and sediment Corg stocks were measured from biomass and shallow sediment cores collected in Moreton Bay, Australia. Samples were collected between 2012 and 2013, from a total of 77 sites that spanned a gradient of water turbidity. Environmental measures of water quality between 2000 and 2013 revealed strong seasonal fluctuations from summer to winter, yet seagrass biomass exhibited no temporal variation. There was no temporal variability in Corg stocks, other than below ground biomass stocks were slightly higher in June 2013. Seagrass locations were grouped into riverine, coastal, and seagrass loss locations and short temporal variability of Corg stocks was analysed within these categories to provide clearer insights into temporal patterns. Above ground Corg stocks were similar between coastal and riverine meadows. Below ground Corg stocks were highest in coastal meadows, followed by riverine meadows. Sediment Corg stocks within riverine meadows were much higher than at coastal meadows and areas of seagrass loss, with no difference in sediment Corg stocks between these last two categories. Riverine seagrass meadows, of higher turbidity, had greater total Corg stocks than meadows in offshore areas irrespective of time. We suggest that Corg stock assessment should prioritise sampling over spatial gradients, but repeated monitoring over short time scales is less likely to be warranted if environmental conditions remain stable.  相似文献   

16.
Quantitative suction sampling was used to characterize and compare the species composition, abundance, biomass, and secondary production of macrofauna inhabiting intertidal mud-flat and sand-flat, eelgrass meadow, and salt-marsh-pool habitats in the Nauset Marsh complex, Cape Cod, Massachusetts (USA). Species richness and abundance were often greatest in eelgrass habitat, as was macroinvertebrate biomass and production. Most striking was the five to fifteen times greater rate of annual macrofaunal production in eelgrass habitat than elsewhere, with values ranging from approximately 23–139 g AFDW m2 yr?1. The marsh pool containing widgeon grass (Ruppia maritima) supported surprisingly low numbers of macroinvertebrates, probably due to stressfully low dissolved oxygen levels at night during the summer. Two species of macroinvertebrates, blue mussels (Mytilus edulis) and to a lesser extent bay scallops (Argopecten irradians), used eelgrass as “nursery habitat.” Calculations showed that macroinvertebrate production is proportionally much greater than the amount of primary production attributable to eelgrass in the Nauset Marsh system, and that dramatic changes at all trophic levels could be expected if large changes in seagrass abundance should occur. This work further underscores the extraordinarily large impact that seagrass can have on both the structure and function of estuarine ecosystems. *** DIRECT SUPPORT *** A01BY070 00006  相似文献   

17.
We examined the rhizosphere structure of 14 seagrass meadows (seven mixed, three Enhalus acoroides, two Zostera japonica, one Thalassia hemprichii, and one Halophila ovalis) in the Philippines and Vietnam and tested their effect on sediment redox potential by comparing the redox potential in vegetated vs unvegetated sediments. The effect of seagrass photosynthesis on sediment redox potential was tested in an E. acoroides meadow during a short-term (2-day) clipping experiment. In all the meadows, the centroidal depth (i.e., depth comprising 50%) of seagrass belowground biomass was within the top 15 cm sediment layer. Redox potentials in vegetated sediments tended to be higher than those in adjacent unvegetated ones; sediment redox potential anomaly ranged from −61 to 133 mV across the meadows. The centroidal depths of positive redox potential anomaly and seagrass root biomass were significantly correlated across the meadows investigated (type II regression analysis, slope = 0.90, lower confidence limit [CL] = 0.42 upper CL = 1.82, R 2 = 0.59, p < 0.01). Experimental removal of E. acoroides leaves resulted in a decrease in rhizosphere redox potential by 20 mV, further confirming the positive effect of seagrass roots and rhizomes on sediment redox potential and, thus, the general conditions for microbial processes in the coastal zone.  相似文献   

18.
Variability in the abundance and distribution of seagrass-associated fish assemblages was examined at different depths in a temperate bay in southern Australia. Depth differences in seagrass-associated fish assemblages are poorly known but this information is critical given that seagrass loss can occur at specific depths depending on the cause. Overall, 69 species of fish from 26 families were recorded, with higher species richness in shallow than deep beds, with 12 species found only in deep beds and 22 species found only in shallow beds. While the total fish abundance (i.e. abundance of all species recorded) varied between years and seasons, and to some extent between sites, it was significantly higher in shallow than deep seagrass beds in the majority of cases. Although there was some variation between sites, seagrass tended to be longer and have a higher biomass in shallow than deep beds during both spring and autumn throughout the study. A positive relationship between seagrass biomass/length and total fish abundance/species richness was apparent. Assemblage structure tended to be distinct at each depth, with the largest species recorded in shallow seagrass. Large numbers of small schooling fish, such as atherinids, dominated in shallow seagrass but were not found in deep seagrass. Loss of seagrass could therefore have varying implications for distinct assemblages found at different depths.  相似文献   

19.
Decapod crustaceans occupying seagrass, salt marsh edge, and oyster habitats within the St. Martins Aquatic Preserve along the central Gulf coast of Florida were quantitatively sampled using a 1-m2 throw trap during July–August 1999 and March–April 2000. Relative abundance and biomass were used as the primary measures to compare patterns of occupancy among the three habitat types. Representative assemblages of abundant and common species from each habitat were compared using Schoener's Percent Similarity Index (PSI). In all, 17,985 decapods were sampled, representing 14 families and 28 species. In the summer sampling period, mean decapod density did not differ between oyster and seagrass habitats, which both held greater densities of decapods than marsh-edge. In the spring sampling period oyster reef habitat supported greater mean decapod density than both seagrass and marsh-edge, which had similar densities of decapods. Habitat-specific comparisons of decapod density between the two sampling periods indicated no clear seasonal effect. In summer 1999, when seagrasses were well established, decapod biomass among the three habitats was not significantly different. During spring 2000, decapod biomass in oyster (41.40 gm−2) was greater than in marshedge (4.20 gm−2), but did not differ from that of seagrass (9.73 g m−2). There was no significant difference in decapod biomas between seagrass and marsh-edge habitats during the spring 2000 sampling period. The assemblage analysis using Schoener's PSI indicated that decapod assemblages associated with oyster were distinct from seagrass and marshedge habitats (which were similar). The results of this study suggest that in comparison to seagrass and marsh-edge habitats, oyster reef habitats and the distinct assemblage of decapod crustaceans that they support represent an ecologically important component of this estuarine system.  相似文献   

20.
The fauna of seagrass-covered mud banks in Florida Bay, documented in the mid 1980s prior to recent seagrass die-off, phytoplankton blooms, and other ecosystem changes, was reexamined in the mid 1990s for faunal changes that might be associated with environmental perturbations. During both decades, decapod crustaceans and fishes were collected with 1-m2 throw traps from seagrass beds at six sites that differ in the amount of freshwater and/or marine influence and in seagrass community metrics. The most common faunal changes were declines in seagrass-canopydwelling forms and increases in benthic forms. At three sites with relatively lush seagrass meadows, above-ground seagrass standing crop declined and abundance of the benthic predatory fishOpsanus beta increased. The degree of faunal change among these sites appeared to be related either to salinity variability or to the degree of exposure to the ecosystem changes that have taken place in Florida Bay. At two sites with poorly developed seagrass meadows, seagrass standing crop and canopy height did not change significantly between decades, but there was an increase in shoot density and total leaf area. The animal communities at these sites were characterized by significant increases in the abundance of benthic crustaceans. At the site on the edge of Rankin Lake, the basin where seagrass die-off was first observed in Florida Bay during 1987, seagrass standing crop, canopy height, shoot density, and leaf area declined significantly between decades, but species richness of both crustaceans and fishes increased. The abundance of canopy-dwelling crustaceans and fishes declined markedly at this site, whereas the abundance of benthic forms less dependent on seagrass cover generally increased. In retrospect, we believe the fauma at this site during the 1980s, characterized by high productivity but few species, was already showing signs of the stresses that led to the seagrass die-off that began in 1987.  相似文献   

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