OOS 77-3
Not just a culinary delicacy: Interactions between oysters and sediment nitrogen dynamics
Over the last century, two prominent changes in temperate estuaries have been accelerating nutrient enrichment and precipitous declines in the population of the eastern oyster, Crassostrea virginica. Oysters reefs provide a wide variety of ecosystem services, including improving water quality through filtration and enhanced denitrification. Filter-feeding by oysters converts phytoplankton to biodeposits, which can fuel sediment denitrification, the conversion of bioavailable nitrogen to N2 gas, a process which ultimately removes excess nitrogen from the system. Because oysters process and remove nitrogen, the limiting nutrient for primary production in estuaries, there is growing interest in using oysters to control eutrophication of coastal systems. Restoration and aquaculture represent two ways to increase oyster biomass within an ecosystem. Oyster aquaculture differs from oyster reef ecosystems in numerous ways including limited predation, lack of biogenic structure and higher density of oysters. These differences can affect the production and accumulation of organic matter on the sediment, and thus sediment denitrification. We investigated how restored intertidal oyster reefs and oyster aquaculture affect sediment fluxes of NOx-, NH4+ and N2. Fluxes were measured from oyster reef sediments, oyster aquaculture sediments and analogous control sediments without oysters.
Results/Conclusions
Oyster reefs enhanced denitrification by 18-275% over the controls, while aquaculture enhanced denitrification by 125%-450% over the controls. Differences between the aquaculture and reef sediments suggest that oyster mediated-denitrification is influenced by multiple environmental factors and interactions between structure, density and predation. Both oyster restoration and aquaculture, can be used to recover the services that oyster provide, while reducing fishing pressure on the native population. Our ability to use oysters to mitigate the effects of eutrophication and to maximize provisioning of services remains limited by our understanding of factors that influence these functions.