Scientists believe they have found one cause of a mysterious wasting disease that has caused a mass die-off of sea stars in some local waters.
Divers at Whytecliff Park in West Vancouver first reported the problem to scientists at the Vancouver Aquarium last fall, when they noticed large populations of previously healthy starfish seeming to liquefy on the spot. The die-off spread quickly, with thousands of multi-armed sunflower sea stars disappearing from waters off Bowen, Hutt and Popham islands.
The phenomenon has since been tracked in pockets up and down the West Coast, as far south as California.
Recently researchers, including two Vancouver Aquarium scientists, published a paper which points to densovirus, a virus commonly found in invertebrates, as likely contributing to the sea stars' disappearance.
The syndrome afflicting the species causes a particularly swift and nasty death for the sea stars, in which their limbs fall off, their body wall ruptures and their organs drift out into the ocean.
The sea stars — which can grow up to two feet across and have 26 arms — were hugely abundant until last year, numbering in the thousands at some of the locations where the die-offs happened, a situation that may have spread disease.
This spring, the disease also appeared to be taking hold in common purple or ochre starfish found in most local tide pools.
The disease also affected sea stars that had been at the Vancouver Aquarium for years — likely because the ocean water used in the tanks also contained the virus.
The paper published by Cornell University researchers this week and co-authored by Vancouver Aquarium scientists Martin Haulena and Jeff Marliave points to densovirus as a major cause of the die-off.
But it doesn't answer all questions, said Haulena, head veterinarian at the aquarium — such as whether a bacterial infection may also be present or what environmental factors may be contributing to the die-off.
"There's probably more to it," he said. "There's always a relationship between the host, parasite and the environment."
For instance, densovirus has been present in marine waters for over 70 years but scientists don't know if there have been previous die-offs on a similar scale.
Other important questions include how the sea star die-off is affecting the marine environment.
Sea urchin populations in Howe Sound have exploded since the sunflower stars — their natural predators — died in massive numbers. The sea urchins are now eating the kelp, which normally provide habitat for fish and other animals including spot prawns.
"The ecology will undergo some kind of change," said Haulena.
Scientists plan to continue tracking impacts on the ecosystem caused by the die-off, as well as the spread of the sea star wasting disease.
