Response of a benthic suspension feeder (Crassostrea virginica Gmelin) to three centuries of anthropogenic eutrophication in Chesapeake Bay

Biogenic reefs built by oysters and other suspension feeders are vital components of estuarine ecosystems. By consuming phytoplankton, suspension feeders act to suppress accumulation of organic matter in the water column. Nutrient loading increases the rate of primary production, thereby causing eutrophication. As suspension feeders consume more organic matter from increasing abundance of phytoplankton, their rate of growth should also increase if they are food limited. We show here that the eastern oyster, Crassostrea virginica (Gmelin), from St. Mary's and Patuxent rivers, Chesapeake Bay, grew faster during anthropogenic eutrophication relative to C. virginica before eutrophication. Growth of shell height, shell thickness and adductor muscle increased after eutrophication began in the late 18th century. After 1860, growth decreased, perhaps reflecting the negative effects of hypoxia, harmful algal blooms, disease and fishing on oyster growth. These results are consistent with the view that an increasing supply of phytoplankton resulting from eutrophication enhanced growth of C. virginica between 1760 and 1860, before oyster reefs were degraded by destructive fishing practices between 1870 and 1930. Alternative factors, such as changes in water temperature, salinity, and fishing are less likely to be responsible for this pattern. These results have implications for restoration of oyster reefs in order to mitigate the effects of eutrophication in estuaries, as well as the paleoecological relationship between suspension feeders and paleoproductivity.