Black Abalone Withering Towards Extinction, Scientists Say

August 9, 2005

Black abalone used to be the most abundant shellfish clinging to the rocks in the intertidal zone from Baja California to Oregon. Now they are all but gone in the southern reaches of their range and beginning to disappear in the north, too.

The intertidal zone is the region where the surf meets the land. Organisms that live there are pounded by waves, blasted by sunlight, and endure wide fluctuations in temperature driven by the rise and fall of the tides.

Black abalone are well-adapted to this harsh lifestyle, according to Fiorenza Micheli, a marine ecologist at Stanford University's Hopkins Marine Laboratory in Pacific Grove, California.

But that's not all the mollusks face.

"They have been decimated by diseases. They have been overfished in places. They are fed upon by sea otters and other animals," Micheli said in an interview with the Pulse of the Planet radio program.

Micheli is part of a group of researchers based on the U.S. West Coast scrambling to understand why black abalone are withering away and what, if anything, can be done to save them.

Black abalone populations once occurred at a density of 60 to 80 individuals per square meter (about 10 square feet) and dominated the seascape in southern California, according to Brian Tissot, a marine ecologist at Washington State University in Vancouver.

The mollusks graze on algae such as seaweed and influence the distribution of other intertidal organisms like mussels and snails. "They also certainly had a cultural role in the past with Native Americans," Tissot said.

The exterior shell is smooth and dark brown to almost black in color. The interior is an iridescent pink and green. Ranging in size from 3 to 8 inches (7.5 to 20 centimeters), the shells were used by Native Americans for everything from bowls to baskets and commonly traded, Tissot said.

Due to concerns about the species's decline, California's black abalone fishery closed in 1993. "[More than] ten years later, we are still not seeing a recovery of these animals, so we are trying to understand why," Micheli said.

Withering Syndrome

According to Tissot, the biggest factor in the black abalone decline is the chronic wasting disease called withering syndrome.

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