Effects of oyster population restoration strategies on phytoplankton biomass in Chesapeake Bay: a flexible modeling approach

Cultural eutrophication in estuaries and other coastal systems has increased over the last 50 yr. Some recently proposed strategies to reverse this trend have included the restoration of bivalve suspension feeders as an ecological tool for reducing phytoplankton biomass. The ecological benefits accruing from such bivalve restoration will be dependent on the characteristics of the estuary, as well as how restoration is implemented. We developed a filtration model to estimate the effect of bivalve restoration on the rate of phytoplankton removal over a range of spatial and temporal scales and used it to compare alternate restoration strategies for the eastern oyster Crassostrea virginica in Chesapeake Bay, USA. Model results suggested that currently accepted restoration goals for oysters in the bay are unlikely to result in significant bay-wide reductions in phytoplankton biomass. This is partially due to low current biomass targets for oyster restoration, but also important are several spatial and temporal mismatches between oyster and phytoplankton biomass that may limit the ecological benefit of oyster restoration. Our model did predict important increases in phytoplankton removal by oysters at the tributary scale, and this effect was dependent on where oyster restoration was achieved and whether restoration and management plans affected the size distribution of oysters. Our findings suggest that the ecological benefit of restoring bivalve populations are variable, and a comparative model analysis of restoration plans in particular systems can be highly beneficial to maximizing the benefit-to-cost ratio of restoration efforts intended to reduce the negative effects of cultural eutrophication.