A Navy research and development center that usually focuses on high-tech communication and surveillance matters is working to boost numbers of one of California's most critically endangered marine animals.
The black abalone, Haliotis cracherodii, is nearly extinct off the Southern California coast. That's due due to a number of factors including historic overharvesting and a bacterial disease called "withering syndrome," which causes the giant sea snails to starve. Listed as Endangered in 2009, the abalone has nonetheless continued to decline in number.
To help counter the decline, scientists at the San Diego-based Space and Naval Warfare Systems Center Pacific (SSC Pacific) have been rearing disease-resistant black abalone larvae in the lab, then transplanting them to appropriate habitat when they reach adulthood. According to SSC Pacific staff scientist Dave Lapota, the transplanted black abalone seem to have a survival rate of about 60 percent, raising hopes that they may help keep the species going off the Southern California coast.
The adult black abalone have been transplanted to appropriate habitat surrounding San Clemente and San Nicolas islands, which are controlled by the Navy. Generally, that means rocky surfaces from the bottom of the intertidal zone downward to depths of about 20 feet.
Those rock surfaces offer a place for abalones to hang on to with their muscular feet, where they feed on drifting algae and various species of kelp. In ideal circumstances black abalone can live up for 75 years or more, growing to eight inches long.
Those ideal circumstances mostly don't happen anymore in Southern California waters. Historically the most abundant large mollusk along the coast from Mendocino to Cabo San Lucas, the black abalone took a major hit in the 1970s. That's when abalone fishermen turned to the species after the related species pink and green abalone began to succumb to overfishing. Hauls of black abalone quickly peaked and then began a steep decline.
In 1985, biologists noticed that some black abalone in the Channel Islands were faring poorly, losing weight and the ability to cling to their rocky habitat. The culprit turned out to be a bacterium, Candidatus Xenohaliotis californiensis, which infected the gastric systems of the snails, causing them to starve slowly. The disease spread from the islands to the mainland coast in short order, and seems to flare up during warm water events such as El Niño.
At SSC Pacific in the late 1990s, Dave Lapota and his colleagues were studying black abalone larvae to see if they might secrete substances that could be used in antifouling coatings. Faced with the prospect of his study subjects going extinct, Lapota realized his lab was in a position to help.
"At the time, we felt that our laboratory at SSC Pacific could also be used for growing the larvae to adult-sized abalone in an effort to increase depleted abalone numbers in offshore waters," Lapota told Defense Department public affairs writer Ashley Nekoui. "Based on our initial undertaking, we realized that we could increase the abundance of remaining populations by transplanting adults offshore in affected areas, thereby increasing recruitment to the impacted populations."
Some black abalone seem to possess resistance to Xenohaliotis infection. Lapota's team transplanted 800 disease-resistant adults to rocky submerged habitat around the Navy's bases in the Channel Islands archipelago.
"Cursory results indicate that 60 percent of the population may have survived and will therefore contribute to new offspring in the area," said Lapota.
Lapota and his team still need to find ways to nurse more larvae into adulthood in the lab, but the preliminary results of their work are good news indeed for black abalone. And the giant snails need that good news: with warmer ocean waters expected as a consequence of human-caused climate change, the species will desperately need any resistance it can get to wasting syndrome.