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Marine Ecology Progress Series

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MEPS - Vol. 432 - Feature article
Haplosporidium nelsoni spores (S) and plasmodia (P) in a rare heavy infection of an oyster, Crassostrea virginica, from lower Chesapeake Bay. Image: Ryan Carnegie

Carnegie RB, Burreson EM


Declining impact of an introduced pathogen: Haplosporidium nelsoni in the oyster Crassostrea virginica in Chesapeake Bay


Reproduction by oysters in low-salinity waters is considered critical for populations in lower Chesapeake Bay because these areas are refugia from oyster diseases and may export larvae to downstream waters. Predominant reproductive contributions from unselected oysters in refugia are thought to have prevented development of disease resistance. Weaving long-term monitoring data with contemporary studies, Carnegie and Burreson examined the response of the oyster Crassostrea virginica to the introduced parasite Haplosporidium nelsoni. Contrary to established assumptions, they found widespread resistance to H. nelsoni that is best developed in populations exposed to consistently intense infection pressure. The authors argue that contributions from unselected oysters in low salinities have been exaggerated, and that reefs harboring resistant oysters in disease-intense mesohaline-polyhaline waters are instead most vital in a restoration context.


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