Disease-resistant black abalone offers restocking hope
06 November, 2007 -
US biologists have discovered that black abalone on the most remote of California's Channel Islands, San Nicolas Island are resistant to the deadly bacterial disease known as withering syndrome.
The discovery may help save these now rare intertidal molluscs from extinction, as scientists hope to soon breed these animals in captivity for release in the wild.
San Nicolas Island has been the site of several severe outbreaks of withering syndrome, said Carolyn Friedman, a professor at the School of Aquatic and Fishery Sciences at the University of Washington in Seattle, explaining the island abalones’ hardiness. They are the descendants of that one percent of the population that survived.
Friedman and her colleague on the California Sea Grant project, Professor Steven Roberts, also at the University of Washington, are now trying to identify which genes are responsible for resistance and the mechanisms by which this resistance is conferred. This work includes studying differences in gene expression between island black abalone and those from Carmel in Monterey, as the animals are subjected to high loads of the withering syndrome pathogen.
“The hypothesis is that these resistant populations have been subject to intense selective pressure,” Roberts said. “The animals we have tested from Carmel have had little or no withering syndrome selective pressure.”
Withering syndrome, which causes severe atrophy of the animal’s foot muscle and is caused by a water-borne pathogen excreted in abalone faeces, occurs in relatively warm water, such as those found in the Santa Barbara Channel. Until recently, waters off the more northerly Carmel have been too cold to trigger outbreaks. As a result, abalone in Carmel have little natural protection against the disease.
Although harvesting black abalone is now banned, ecologist Hunter Lenihan, a professor at the Donald Bren School of Environmental Science and Management at UC Santa Barbara, believes the species will have difficulty recovering on their own. Poaching remains an issue, disease another, he said. The species has become so rare it is now a candidate for protection under the federal Endangered Species Act. With California Sea Grant support, Lenihan and graduate students are trying to identify the conditions necessary to spawn black abalone in a laboratory setting. The goal is to be able to breed disease-resistant animals for release in the wild. Captive breeding would seem a relatively simple task given that red abalone are already farmed commercially. This is not the case, however, as black abalone are an intertidal species, red abalone a subtidal one. Black abalone reproduction seems to require a complex set of conditions that may depend on winds, waves and sea level, Lenihan said. “The females are strong,” Lenihan said. “We have gotten them to spawn. The problem is the males. To get the males to spawn, we are going to have to play the right music and find the right wine.”
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