For years, it seemed that all scientists could do was document the decline of the black abalone. Although they tried to figure out why the mollusk's population was decreasing up and down the Southern California coast, they didn't get anywhere beyond narrowing down the culprit.

Biologists figured out a pathogen was getting into the abalone's intestines, preventing it from digesting food and causing it to start absorbing its own body mass. The abalone's foot, which attaches to rocks and reefs, would waste away, and the mollusk would fall to the floor, where predators quickly dispatched it.

About all that was known was that the "withering syndrome" caused the population to crash in the 1990s, and the Channel Islands — the backbone of the population — lost most of its black abalone. What causes the pathogen is still a mystery.

But scientists think they might have found one clue that could help keep the abalone from nearing extinction. A small group of black abalone off San Nicolas Island seems to be immune to the withering syndrome.

"Certainly there is hope," said Glenn VanBlaricom, a professor with the University of Washington School of Aquatic and Fisheries Science, "but you have to be careful of getting too carried away."

VanBlaricom had been studying black abalone since the 1970s and witnessed its dramatic fall in the early 1990s, when as much as 95 percent of the population died off. Other species of abalone were also dying off because of fishing and disease.

The white abalone was the first marine invertebrate put on the endangered species list. The black abalone is now under consideration for the list.

During VanBlaricom's research, he noticed that one cluster of black abalone on the southwest side of San Nicolas Island seemed to have high numbers.

During a 2002 trip, he noticed juvenile abalones, which weren't being seen anywhere else. This, he thought, could be promising.

He and other researchers at the university collected 100 abalones from the island and another 100 from the waters near Carmel, where the withering syndrome had not yet reached.

They ran an experiment, putting the two different groups into water infected with the withering syndrome. The San Nicolas abalone had a mortality rate of about 10 percent, compared with as high as 90 percent for the Carmel abalone.

Although it is too early to be sure, VanBlaricom said he thinks there might be something in the San Nicolas abalone's DNA that makes it immune to the disease. But whether that small population holds the key to the larger issue is debatable.

If the black abalone is put on the endangered species list, it will likely free more money to study the San Nicolas population. But using the San Nicolas abalone to help shore up the overall population would be problematic.

When abalone propagate, the offspring land relatively close to the parent, so spreading populations is a slow process. And VanBlaricom is reluctant to disturb a population that inhabits only a reef about a quarter-mile long, for fear of messing up a good thing.

The logistics of raising black abalones in a lab and relocating them into nature is also problematic, he said.

"It is an enticing idea, but one of those situations where the devil is in the details," VanBlaricom said.