Infection dynamics of an oyster parasite in its newly expanded range |
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Authors: | Susan E Ford Roxanna Smolowitz |
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Institution: | (1) Haskin Shellfish Research Laboratory, Rutgers University, 6959 Miller Avenue, Port Norris, NJ 08345, USA;(2) Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543, USA |
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Abstract: | Over a 2-year period in 1990 and 1991, coincident with a pronounced warming episode, Dermo disease outbreaks in the oyster,
Crassostrea virginica, caused by the parasite Perkinsus marinus, occurred over a 500-km range from Delaware Bay to Cape Cod, in the northeastern United States. The parasite had not previously
been recorded or known to cause mortalities in this region. To document infection patterns and levels in this region several
years after the initial outbreaks, and to compare them with those in the parasite’s historic southern range, we deployed and
sampled oysters from 1996 to 1998 at multiple sites spanning the expanded range. During this 2-year period, the parasite was
documented to occur in oysters at high prevalences throughout the new range, in sites varying from small, enclosed embayments
to large estuaries, and in both cultured and wild-set oysters. Infection and mortality patterns, and levels were similar to
those in southern locations where the parasite has been enzootic for at least decades. The persistence of high P. marinus infection levels in the new range after the initial expansion is probably due to several factors: (1) winter temperatures
continued to increase during the 1990s and early 2000s, albeit at a slower rate than in 1990–1991, facilitating overwinter
survival of the parasite; (2) many oyster-growing sites in the northeast are in relatively shallow water in which summer temperatures
offer ample time for the parasite to proliferate and spread; and (3) the combination of high parasite burdens and high host
densities in oyster farms results in an abundance of parasites and high transmission rates. Colder winters and high rainfall
after 2002 reduced prevalences in some regions, but P. marinus can survive low temperatures and low salinities, and epizootic conditions are likely to return if temperatures rise again,
as predicted by climate-change models. |
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