A disease that has killed millions of sea stars on the west coast of North America since 2013 has been confirmed as the cause of death of some of the creatures in Haida Gwaii, marking the first time that the illness has been found in the waters of northern British Columbia.
“I have confirmation that it is indeed the SSWD [sea star wasting disease] they have been seeing in the south,” said Aggie Cangardel, a marine biologist with the Haida Fisheries Program. “We cannot do anything with this news. As with the rest of the coast afflicted, we hope to see disease-resistant juveniles in the future.”
Since 2013, sea star deaths have been recorded as far north as Sitka, Alaska, and as far south as Baja, California. The disease — so named because the invertebrates appear to deflate and then develop lesions before their tissue disintegrates — has been reported in more than 20 species.
In November 2014, researchers at Cornell University identified the cause of the disease as sea star associated densovirus, a type of virus commonly found in invertebrates, and suggested that it has been a low-level threat for many years, with signs of the virus present in museum samples of sea stars collected as far back as 1942. The virus’ recent epidemic levels could be due to sea star overpopulation, environmental changes, or mutation of the virus, the researchers found.
After geoduck clam divers from Haida Gwaii reported seeing what looked like sick sea stars in January, Cangardel collected samples during the Haida Fisheries Program’s annual herring spawn survey in April. “On probably 70 to 80 per cent of our transects, we saw some evidence of this occurring,” she said. “When I was diving, I started picking up bits and putting them in my pocket so that I would be able to send them off for testing, because you never know whether it’s a sick sea star or if it was just ripped up by a sea lion and left there.” The samples Cangardel collected were sent to the Vancouver Aquarium for testing.
Cangardel noted that sightings of what were believed to be sea stars suffering from the disease had been logged on seastarwasting.org in August 2014. “You can see there was someone who had seen some in Gwaii Hanaas, which is the national park where we were diving during the survey, although I don’t believe any samples were taken.”
Cangardel and her team had last dived in the area in October 2014, and they didn’t notice anything unusual about the sea stars at the time. “Transects for the herring survey are pretty much the same each year, so we’re able to say this is entirely different from last year.”
Sea stars are keystone species, which means that they keep other populations in check and therefore have a pivotal role in the ecosystem. “Because they’re so wide-ranging with their prey — mussels, limpets, snails, barnacles — their effects are felt,” said Cangardel, who described the sea star deaths as a mass mortality event. “These events do occur, and they have this immediate, shocking factor to them, but we can’t and we shouldn’t speculate about what could happen.”