Parasitic diseases in Rhode Island oysters

Marta Gomez-Chiarri
University of Rhode Island

Wednesday, September 1, 1999
3:00 p.m.—Pacific Forum

Diseases caused by parasites like Perkinsus marinus (causative agent of Dermo disease) and Haplosporidium nelsoni (causative agent of MSX) have devastated oyster populations in areas of the eastern coast of the United States, with the corresponding ecological, economic, and social impact. In particular, Dermo disease has been the cause of serious epizootics in the Chesapeake and Delaware Bays that have decimated these oyster populations. Although originally thought to be restricted to the Gulf of Mexico to Delaware Bay, the range of Dermo disease has extended northward to include all of the Atlantic Coast of the United States. Some researchers attribute this expansion mainly to an upward trend in winter and spring water temperatures.

We have determined the geographical and seasonal pattern of Dermo disease in oysters from Rhode Island waters. Dermo disease shows a strong seasonal pattern that seems to be determined by changes in temperature and salinity. The high temperatures experienced by the oysters in the late summer favor the proliferation of the parasite and the development of heavy infections, leading to oyster mortality. However, temperature and salinity alone do not entirely explain the patterns in geographical distribution and the variability in infection intensity and oyster mortality. These contrasting patterns of infection indicate that complex interactions between environmental and biological variables influence infection intensity and distribution.

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