From: Associated Press
Published August 22, 2005 12:00 AM

Parasite Preying on Shrimp in Oregon

PORTLAND, Ore. — Biologists are concerned about a non-native parasite that's preying on mud shrimp up and down the Oregon Coast's estuaries, potentially playing havoc with sensitive ecosystems.

The newcomer -- called the Griffen's isopod -- has been spotted in Tillamook, Yaquina, Alsea and Siletz bays in Oregon and Willapa Bay in Washington.

Mud shrimp are commonly used by humans as fish bait, but they are important prey for birds, fish and other animals. They live in intertidal mudflats, where their large populations filter as much as 80 percent of the water each day.

John Chapman, an invasive-species expert with Oregon State University, is speculating that the parasites arrived on the West Coast in ballast water released by ships. Researchers are estimating that the parasite may have infested as much as 80 percent of breeding adult mud shrimp.

After entering a mud shrimp's gill chamber beneath its carapace, or shell, the parasite sucks the animal's blood and other nutrients, destroying its reproductive system.


"We can't tell yet how much the shrimp's death rate goes up when they're infected," said Chapman, who heads the Biological Invasions Program at OSU's Hatfield Marine Science Center in Newport. "But they're all done reproducing. They become zombies."

Female mud shrimp usually produce 1,800 to 11,000 eggs. But a recent examination of 42 female mud shrimp from Yaquina Bay by Chapman and ecologist Brett Dumbauld of the U.S. Department of Agriculture found only eight had eggs -- the rest had been infested with the parasite. Only one of the eight females with eggs had the parasite, and she had only 15 eggs.

The parasite, which is only about three-quarters of an inch wide, was first spotted in Oregon about 20 years ago, but not fully identified until this past winter.

Chapman said Japan is the only other place the parasite has been found, but it's unclear where the organism originated. He said the only way it could have crossed the ocean would have been by "human intervention."

Researchers said they don't yet know enough about the parasite to determine whether it can be stopped.

Source: Associated Press

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