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Geographic website, 9 Aug 05 Black Abalone Withering Towards Extinction, Scientists Say John Roach for National Geographic News 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. "Starting in the late 80s, it just eliminated them very quickly in southern California and has worked its way up the coast," he said. The syndrome is caused by a bacterium. It gets into the digestive tract, causing the mollusks to shrivel, said Melissa Neuman. Neuman is the abalone recovery coordinator for the National Marine Fisheries Service in Long Beach, California. "By the time we see the foot withering, it's too late," she said. Within a few months, the disease can wipe out more than 90 percent of a population. And it's nearly impossible for black abalone to recover when their populations are so obliterated, Tissot said. The species reproduces through a process known as broadcast fertilization: males release their sperm and females their eggs into the water column where they come together. Babies then latch onto cracks and crevices in the rocks where they develop. Normally, the sheer abundance of sperm and eggs means a new generation will arise. "But when mortality happens and densities are low, they are not close enough for that to happen," Tissot said. Monitoring, Hoping According to Tissot's research, the bacterium that causes withering syndrome can survive in cold water but the disease only takes hold when the ocean temperature rises above 65 degrees Fahrenheit (18 degrees Celsius). For example, during the El Niņo events of 1993 to 1994 and 1997 to 1998, researchers observed withering syndrome creep up the coast towards Big Sur, California. El Niņo is a periodic warming of the Pacific Ocean that influences weather patterns around the world. Melissa Miner is a marine biologist at the University of California, Santa Cruz, who monitors the effect of withering syndrome on black abalone. She said healthy populations remain north of San Luis Obispo, California, but the future is uncertain. "The thing we're worried about is the disease is present in populations all the way up to San Francisco," she said. Miner and her colleagues hope that the colder waters in the north will prevent the disease from taking hold, but the possibility of another strong El Niņo and the gradual ocean warming due to the Earth's changing climate are cause for concern. According to Tissot, another hope is that some populations will develop immunity to withering syndrome, "but we've never seen that." Meanwhile, Neuman and her colleagues with the National Marine Fisheries Service are conducting a status review of black abalone to determine if the mollusks warrant a designation as either threatened or endangered under the U.S. Endangered Species Act. The review should be completed by mid 2006. "We're trying to be proactive," she said. links Related articles on Wild shores of Singapore |
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