Development of disease resistance in oysters has profound implications for Chesapeake Bay restoration strategies, according to a new study by researchers at the Virginia Institute of Marine Science, Gloucester Point.

The study, by VIMS professors Ryan Carnegie and Eugene Burreson, appears in the recent issue of Marine Ecology Progress series. David Malmquist, director of communications at VIMS, said the study is based on 50 years of VIMS research on the prevalence of MSX disease among the native eastern oyster, Crassotrea virginica.

MSX is caused by the single-celled parasite Haplosporidium nelsoni, and first appeared in Chesapeake Bay in 1959, Malmquist said. MSX—combined with other factors including over-harvesting, a decline in water quality and a second parasitic oyster disease Dermo—pushed the bay’s oyster population to one percent of historical levels, a VIMS report said.

"Our results point to substantial reproduction by disease-resistant oysters in the high-salinity areas where the parasite causing MSX thrives," Carnegie said. "We thus argue that reefs in areas of higher salinity should be the focus of conservation and restoration efforts, not just those in disease-free lower salinity areas.

"We basically need to confront the diseases head-on where they are most active," Carnegie added, "rather than avoiding them by working in low salinities. It’s in the high-disease areas that resistance is developing so rapidly, so restoration efforts should be focused there."

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