| The use of bivalve suspension-feeders has been suggested as a means to improve water quality though biofiltration. However, the net effect on water quality is determined by a balance between biofiltration, biodeposition to and subsequent nutrient regeneration from the sediments. In shallow water environments, these and other related ecosystem processes are closely coupled. Water flow is an important aspect of this coupling, supplying seston to the bivalves, and regulating benthic-pelagic nutrient fluxes through mass transfer limitation and resuspension.; The effects of juvenile eastern oysters (C. virginica) and water flow on phytoplankton biomass and on nutrient regeneration were studied in 1 m deep experimental ecosystems. A coupled large 1000 L system with 1 m2 sediment surface area and a coupled small 100 L system with 0.1 m2 sediment surface area were developed by linking a tank to an annular flume or a Gust microcosm, respectively. These new experimental ecosystems had realistic water column mixing, moderate shear velocities of ca. 0.6 cm s−1, and realistic ratios of water column mixing to benthic shear velocity, overcoming flow limitations of many previous designs. For comparative ecosystem experiments, equal densities of oysters were added to the large and small coupled systems and to standard, uncoupled tanks scaled in volume, shape, and sediment surface area to the coupled systems. In addition, uncoupled tanks without oysters were used. To eliminate confounding effects such as macroinfauna, defaunated sediments with low nutrient and gas effluxes were prepared following newly developed techniques.; Through complex and indirect relationships, oysters, enhanced shear velocity, and mesocosm shape significantly affected microphytobenthos (MPB) biomass by affecting light penetration to the bottom and MPB erosion, thereby altering benthic-pelagic coupling and biogeochemical fluxes. Water column nutrient concentrations were not affected significantly by oysters and flow, but trends suggest that soluble reactive phosphorus and dissolved inorganic nitrogen concentrations may have been higher in uncoupled tanks with oysters compared to coupled tanks with oysters. Appropriately scaled whole ecosystem approaches further varying water flow and biological parameters are needed to further elucidate the ecological role of bivalves on benthic-pelagic coupling. |
