Characteristics of Crassostrea ariakensis (Fujita 1913) and Crassostrea virginica (Gmelin 1791) in the Discharge Area of a Nuclear Power Plant in Central Chesapeake Bay

Abstract

Since 1978, the Maryland Department of Natural Resources has investigated the uptake and depuration by C. virginica of radionuclides released by the Calvert Cliffs Nuclear Power Plant (CCNPP), which is located on the western shore of Chesapeake Bay in southern Maryland. This ongoing program presented a unique opportunity to compare radionuclide transfer dynamics and other parameters such as growth, mortality, disease status, and meat condition for Crassostrea virginica and C. ariakensis in a side-by-side, in-situ environmental setting. Introducing the Asian oyster, C. ariakensis, into Chesapeake Bay has been proposed to help restore an oyster population to historical levels, to enhance the Bay ecosystem, and to contribute to the revival of the commercial oyster fishery. The population of the indigenous C. virginica has declined dramatically throughout the bay in part as a result of infection by two non-native protozoan parasites that cause MSX (Haplosporidium nelsoni) and Dermo (Perkinsus marinus) diseases. Other factors including habitat loss, reduced water quality, and overfishing have also reduced population size. Crassostrea ariakensis is known to be more tolerant to these diseases and thus may have greater potential for survival and growth in Chesapeake Bay than the native oyster. Triploid C. ariakensis and diploid C. virginica were immersed in cages in the vicinity of the CCNPP discharge for two exposure periods between July and December 2004. After retrieval, oysters were analyzed for radionuclide concentrations, growth rate, mortality, disease status, and meat condition. Fouling of oysters and cages was also observed. Quantities of radionuclides released by the CCNPP for both exposure periods were insufficient to produce detectable concentrations in either C. virginica or C. ariakensis, precluding a comparison of uptake of Co58, Co60, or Ag-110 m, radionuclides that have been detectable historically. Shell lengths were not significantly different between the two species for the two sampling periods, despite the fact that there were considerable age differences between them, but C. ariakensis did show a greater rate of growth. Meat weights and condition indices for C. ariakensis were significantly greater than for C. virginica (P < 0.01). Mortality and Dermo prevalence and intensity were also significantly greater for C. virginica than for C. ariakensis (P < 0.01). Although quantities of radionuclides were insufficient to produce detectable concentrations in either species, this study provided a unique opportunity to examine C. ariakensis in an area of the Maryland Chesapeake Bay where C. ariakensis has not previously been observed.