The Regional Spatial Structure of Parasites and Pathologies in Oysters and Mussels in the United States: 16 Years of Mussel Watch.

The Mussel Watch Program sampled bays on the East, Gulf, and West coasts of the United States over a period of 16 y. Analytical protocols included the recording of parasites and pathologies. Oysters ( Crassostrea virginica) harbored significantly more parasitic taxa than mussels (Mytilidae). Cases where body burden was higher in mytilids were exclusively eukaryotic parasites, trematode metacercariae and trematode sporocysts. Oysters had higher body burdens of Nematopsis, alimentary tract ciliates, prokaryotic inclusions, and a number of unique taxa including haplosporidians, Perkinsus marinus, cestodes, and nematodes. Major pathologies were much more common in mytilids. For oysters, many parasitic taxa were more common in the Gulf of Mexico, including Nematopsis, P. marinus, trematode sporocysts, and nematodes. For mytilids, most parasites and pathologies were more common on the East Coast. Most parasite distributions were clinal on the East and West coasts, with clear relationships to well-known provincial boundaries. West Coast mytilids and East Coast oysters showed a similar trend toward increased parasite weighted prevalence in the south. The greater body burdens in Gulf Coast oysters might be a continuation of this trend. East Coast mytilids offer an opposing trend with higher body burdens in the Gulf of Maine. An increasing incidence of pathologies in mytilids at northern latitudes on both coasts runs contrary to the antithetical trends on the two coasts for parasite weighted prevalences. Within the parasite-rich Gulf of Mexico, oysters from the Texas coast were notable for their higher parasite body burdens. Some parasites and pathologies tended to have low variance-to-mean ratios and thus be identified as having even distributional patterns. Others showed a large range of weighted prevalences within a region and thus had contagious distributional patterns. With the exception of P. marinus, most of the contagious parasites were single celled. The multicellular taxa were more uniformly distributed: they tended to have much lower variance-to-mean ratios. Likely, the difference in spatial distribution between single-celled and multicellular taxa is due to the tendency for single-celled organisms to proliferate within the host or, being small, the ability to accumulate in larger numbers within the host. [ABSTRACT FROM AUTHOR]