and Climate / Marine Life

Parasites Share our Love of Oysters


Perhaps you’ve eaten an oyster – if so, you are far braver than me, but have you even taken the time to ask an oyster how it’s feeling? I hadn’t until I started working on a class project looking at the relationship between oyster health and climate. For over two decades, NOAA (National Oceanic and Atmospheric Association) ran a program called Mussel Watch. During this program, information was collected on contaminants and parasites in oysters and mussels all around the US. It was one of the longest running ecological monitoring programs before ending in 2010. After taking a look at the Mussel Watch data set for my project, I found out it’s hard out there for an oyster! They are susceptible to all kinds of parasites and infections. Here’s a quick look into several parasites that infect our bivalve friends.

Dermo — the disease caused by the protist Perkinsus marinus. Protists are single celled eukaryotic organisms, a well-known example of which is Plasmodium, which causes malaria.  P. marinus infect pretty much all parts of an oyster including the gills, intestines, connective tissues, and cells within the blood. Once an oyster is infected their muscles shrink, and they cannot eat, produce blood cells, grow or reproduce. As you might imagine, the prognosis for an oyster with dermo isn’t good. Dermo has caused mass mortality in oyster populations along the East and Gulf coasts.

Cestode parasitism — cestodes are a type of parasitic flatworm related to tapeworms. Oysters act as an intermediate host for cestodes. The worms inhabit the digestive system of the oyster before they move on to infect elasmobranchs (sharks and rays). While no oyster wants to be infected with a bunch of flatworms, the prognosis for this condition isn’t as bad as dermo. Heavy infection is known to slow growth and reproduction in some cases, but even heavily infected oysters sometimes show no symptoms.

Nematopsis parasitism — despite the similar name, these marine critters are not related to nematodes. Nematopsis is a genus of protist that contains multiple species that parasitize oysters. They infect the gills, mantle, and muscles. Infection of the adductor muscle can diminish an oyster’s ability to keep its shell closed. Once again, things don’t look good for an oyster with Nematopsis infection. The mortality rate of oysters in aquaculture beds that have been infected can be over 50%.

We don’t have to worry about getting any of these three parasites, but we can worry about how they can hurt the marketability of affected oysters. Some parasites are impacted by temperature, proliferating more as temperature increases. As ocean temperatures rise, so too may the prevalence of certain oyster diseases. Keep an eye on UNder the C where I will post about any findings my classmates and I make on this front!

Check out these sites and articles for more info –

Kimbrough, K. L., W. E. Johnson, G. G. Lauenstein, J. D. Christensen and D. A. Apeti. 2008. An Assessment of Two Decades of Contaminant Monitoring in the Nation’s Coastal Zone. Silver Spring, MD. NOAA Technical Memorandum NOS NCCOS 74. 105 pp.

Prytherch, H. F. (1940). The Life Cycle and Morphology of Nematopsis ostrearum, Sp. Nov. A Gregarine Parasite of the Mud Crab and Oyster. Journal of Morphology. 66: 39–65. doi:10.1002/jmor.1050660106



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