Shrimp Attacked by Blood-Suckers

A parasitic, aquatic crustacean on the West Coast threatens to wipe out mud shrimp populations in estuaries.

The crustacean, known as Griffen's isopod (inset above), enters the shrimp's gill chamber and sucks the shrimp's blood and nutrients. Once infested, the shrimp cannot reproduce. Normally females produce 1,800 to 11,000 eggs.

Invasive species expert John Chapman of Oregon State University believes the parasite is a non-native species due to its abnormally large size and occurrence in Japan. They were most likely introduced to the West Coast by ballast water released from ships.

"If we're right, this may be the most significant ballast water introduction of a non-native species yet discovered on the West Coast," Chapman said. Reports indicate the isopod has spread as far south as Santa Barbara, California and as far north as British Columbia.

Mud shrimp dominate estuaries in Oregon, and their deaths could have large impacts. While people use them primarily as fishing bait, they are important food resources for birds and fish. They are filter feeders and in some estuaries they filter as much as 80 percent of the water daily.

Chapman and his colleagues have examined mud shrimp populations all summer, all of which were infested with the parasite. "Nothing we know already provides reason to be optimistic," Chapman said.

--Bjorn Carey

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Credit: Brett Dumbauld