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Where Go the Oysters Go the Parasites

Ever wonder how a parasite finds its host in the ocean or why some hosts have more parasites than others? According to a recent study, it may be simpler than you think: the same physical forces as their hosts are concentrating parasites. MSC graduate student, Tanya Rogers, along with faculty members Jon Grabowski, Randall Hughes, and David Kimbro, along with external colleagues, collaborated on this research, which appeared recently in Oecologia.

By experimenting with various spatial organizations across 1,000km of the southeastern Atlantic, the team found a relatively simple explanation for host-parasite hot spots. Different biotic and abiotic factors can lead to the large spatial variability of the parasitic pea crab on its oyster host. These small crabs live inside oysters and are a type of kleptoparasite, meaning they steal food from their hosts.

An oyster gathers food by filtering water over its gills, trapping edible particles on its gills, and carrying those particles to its mouth using cilia (tiny hairs). Pea crabs sit on the gills and pick out some of the food the oyster traps before the oyster can consume it. By scurrying around inside oysters, pea crabs can also damage the gills mechanically. The pea crabs, like most parasites, don’t kill their hosts, but they can certainly affect the oysters’ overall health. Down South, if you order oysters on the half shell, you can sometimes find oyster pea crabs in the oyster. The egg-bearing females look like squishy orange peas. Since they spend their entire life protected inside an oyster, the shells of female pea crabs aren’t hard like most crabs and their claws are very tiny.

These researchers used a genetically-similar group of oysters (reared in the laboratory) to test the prevalence of infection at several sites throughout the Atlantic coastline, and compared the infection to temperature, submersion time, length of exposure and latitude. Interestingly, their results suggest that abiotic factors affecting oyster spat recruitment may be similarly affecting pea crab recruitment, leading to hotspots of infection in some areas over others.

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