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Marine Ecology Progress Series

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MEPS 325:301-309 (2006)  -  doi:10.3354/meps325301

Limits to top-down control of phytoplankton by oysters in Chesapeake Bay

Lawrence R. Pomeroy1,*, Christopher F. D’Elia2, Linda C. Schaffner3

1Institute of Ecology, University of Georgia, Athens, Georgia 30602-2202, USA
2Center for Science and Policy Applications for the Coastal Environment, University of South Florida, 140 7th Avenue S, St. Petersburg, Florida 33701-5016, USA
3Department of Biological Science, School of Marine Science, Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062, USA

ABSTRACT: Restoration of the oyster Crassostrea virginica population in Chesapeake Bay is often advocated as an easy solution for controlling phytoplankton blooms. Even at their pre-colonial densities, oysters are unlikely to have controlled blooms, despite the fact that sediment cores suggest that pre-colonial spring blooms were smaller than at present. Lack of access to all bay water and low springtime filtration rates would make it impossible for oysters to control the spring bloom and the resulting summer hypoxia. Previous studies have overestimated potential oyster filtration rates, because they extrapolated summer rates to spring conditions that are 20°C cooler. Previous studies have also assumed that oysters have access to all phytoplankton, without considering the spatial separation. In Chesapeake Bay, oysters and the spring bloom are separated horizontally owing to the size of the bay and its small tidal amplitude. Indeed, a multi-species guild of suspension feeders now present in the bay should have a filtration capacity approaching that of pre-colonial oysters, but it does not control the bloom. Actual oyster filtration potential must be lower than many advocates of oyster restoration assume, and replenishing the bay with oysters is not the means of controlling blooms and hypoxia.

KEY WORDS: Chesapeake Bay · Hypoxia · Oysters · Eutrophication

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