Linking community structure to carbon cycling: evidence of cascading effects in an experimental seagrass system.
Spivak, Amanda*,1, Canuel, Elizabeth 1, Duffy, J. Emmett1, Richardson, J. Paul1, 1 College of William and Mary, Gloucester Point, VA
ABSTRACT- Coastal seagrass ecosystems are complex habitats that are increasingly influenced by natural and human perturbations. Such disturbances contribute to ongoing biodiversity loss and subsequent changes in community structure. For example, overharvesting of predators in eelgrass systems may cascade down to affect animal density at intermediate trophic levels and algal and plant biomass and productivity. In turn, altered community structure may affect the magnitudes and pathways of carbon flow. Using an experimental eelgrass system we tested effects of changing food chain length (number of trophic levels) and grazer species diversity on whole ecosystem production, sediment organic carbon accumulation and composition, and sediment microbial response. Whole ecosystem oxygen production and consumption were sensitive to both food chain length (presence of predatory crabs) and grazer diversity. Sediment algal biomass, however was only significantly affected by grazer diversity. Food-web manipulations had little influence on sediment organic matter (SOM) quantity. SOM quality, however, was strongly affected by changing food chain length and grazer diversity. Lipid biomarkers, proxies for OM sources, indicated that grazer diversity affected both detrital (total fatty acids) and recently deposited OM (phospholipid-linked fatty acids). Grazer species composition influenced SOM lability (polyunsaturated fatty acid content) and strongly affected sediment bacterial biomass (branched fatty acid concentration). These data demonstrate that biodiversity within trophic levels, the number of trophic levels, and their interaction significantly influence not only biomass accumulation but also carbon dynamics and geochemical processes in marine sedimentary ecosystems.
Key words: biodiversity, food-web, seagrass, SOM
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