Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Kimberly S. Reece


The eastern oyster, Crassostrea virginica, once an integral part of the ecology and economy of Chesapeake Bay, has been severely depleted. Factors leading to the decline of the eastern oyster include over-harvesting, environmental degradation and disease pressure caused by the protozoans Haplosporidium nelsoni and Perkinsus marinus, known commonly as MSX and Dermo, respectively. Studies regarding the feasibility of introducing a nonnative oyster to the Bay were initiated, and field-based research on an Asian oyster, Crassostrea ariakensis, suggested that it might be a viable species for introduction. Research surrounding the proposed introduction has focused on recommendations such as those from the International Council for Exploration of the Seas, suggesting that the "ecological, genetic and disease relationships of the species in its natural range and environment" be examined. In order to assess the disease risks associated with C. ariakensis, a parasite survey of oysters collected from China, Japan and Korea was undertaken to examine the pathogens associated with C. ariakensis in its natural range. The protozoan parasites, Perkinsus olseni and a new Perkinsus sp., as well as multiple genetic strains of molluscan herpesvirus, were discovered using molecular diagnostic methods. Molluscan herpesvirus and Perkinsus spp. protozoans are known to cause mortality of many commercially important bivalve species. Characterization of the new Perkinsus sp. included a comprehensive analysis of three DNA loci along with histological examination of the Perkinsus sp. cells in preserved tissue sections. Challenge experiments were undertaken using P. olseni and the new Perkinsus sp. in order to assess the transmission risk of these exotic microbes to the eastern oyster and the hard clam, Mercenaria mercenaria. The laboratory experiments suggest that bivalve shellfish native to Chesapeake Bay may be susceptible to the alien Perkinsus spp. associated with C. ariakensis. In addition, C. ariakensis may acquire moderate to lethal infections of P. marinus under stressful conditions. In light of the proposed introduction of C. ariakensis, it appears that there is a great disease risk associated with this Asian oyster species with the potential to have a negative impact on the naive shellfish populations of Chesapeake Bay.



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