While diving at one of his favorite sites in Washington State's San Juan Islands, Evergreen College student and recreational scuba diver Nick Brown became alarmed. It was not a diving emergency; his alarm was ecological. "We were swimming along a beautiful wall counting fish when I saw what I thought looked exactly like Ciona savignyi."

That would mean trouble. C. savignyi is a nonnative animal that conservationists in the region were on the lookout for. Brown had learned to identify it, and other potential ecosystem threats, as a participant in a volunteer fish and invertebrate monitoring program supported by UC Davis.

"I was fairly certain it was the real thing, even though it had never been reported in the San Juan Islands," said Brown, who took a picture and reported the sighting.

Brown is one of 300 people trained in Washington by the UC Davis marine ecosystem program named the SeaDoc Society. The trainings are given in concert with the Reef Environmental Education Foundation (REEF), an organization of divers and other marine enthusiasts. As they dive in the region, Brown and the other volunteers gather information about marine fish and invertebrate populations, and keep an eye out for nonnatives like C. savignyi. Their data are collected using a standardized method and can be viewed on the REEF Web site.

Recently, SeaDoc Society Chief Scientist Joe Gaydos and REEF instructor Janna Nichols confirmed Brown's sighting. "We didn't find anything on the first dive," reported Gaydos, "but on the second dive we saw the bad guys." They destroyed the four C. savignyi individuals they found and will re-survey the site this spring.

There are about 100 species of animals similar to C. savignyi that are native to Puget Sound. They are tunicates (called urochordates by scientists), and they normally filter water and feed on plankton. But invasive tunicates have the ability to completely cover over and smother native species. In November 2005 a small clump of C. savignyi was discovered at Sund Rock in Hood Canal; a year later there were thousands.

"I know these critters like a bad migraine," said Nichols, "and I'm not happy about seeing them in the San Juans, but I couldn't be happier that our volunteer scuba diver monitoring network is working."

Pam Meacham, the aquatic invasive species coordinator at the Washington Department of Fish and Wildlife, agreed. "Early detection is our best hope for controlling the spread and eradicating it if possible."

Divers who find an invasive tunicate are asked to take a picture and report the sighting to Meacham at (360) 902-2741.

The SeaDoc Society works to ensure the health of marine wildlife and their ecosystems through science and education. It is a program of the UC Davis Wildlife Health Center, in the School of Veterinary Medicine.