Starfish -wasting -disease _2014_10_17
Sea Star Wasting Disease (SSWD) causes sea stars to become limp, grow lesions and eventually disintegrate. Image: Alison Leigh Lilly, Flickr

All along the Pacific Coast of North America, from Baja California in Mexico to southern Alaska, sea stars (or starfish, if you prefer) have been dying. Nearly twenty species of asteroids – those sea stars that are members of the class Asteroidea – have been afflicted. Combined with the wide geographic extent, this is one of the worst epidemics of Sea Star Wasting Disease (SSWD) that has ever been recorded. And until now, nobody knew just what caused the sea stars to become limp, grow lesions and eventually disintegrate. Today, researchers led by Cornell University microbiologist Ian Hewson announced the discovery of a virus they believe causes the disease. 

This is exciting not just because it brings researchers one step closer to understanding the illness that is wiping out sea stars all along the coastline, but also because the virus is among the first known to infect echinoderms, the phylum that includes the asteroid sea stars. Marine viruses, according to Hewson, are underappreciated and understudied when it comes to understanding the population dynamics of marine ecosystems. 

After discovering the identity of the virus – the researchers are calling it the 'sea star-associated densovirus' or SSaDV – Hewson and his colleagues wanted to see just how unique it was. They sampled some sea stars from along the eastern coastline of the US as well as some from the Mystic Aquarium in Connecticut, and found the virus present in those populations as well, though not in the same epidemic proportions as in the west. That means the virus occurs elsewhere in the world's oceans, rather than just along the eastern Pacific Rim.

The research team then turned to preserved specimens, sea stars collected from the Pacific coast of North America over the last hundred or so years by natural history museums. They found that SSaDV has been present along the Pacific coast for at least 72 years!

This, of course, raises intriguing new questions: if the virus has been swimming around coastal ecosystems for so long, why has it only become an epidemic over the past two years? Why are the Pacific communities suffering so much while the Atlantic ones seem to be doing fine? And what will the long-term consequences of the current outbreak be for coastal ecology, given the important role that sea stars play as predators? Hewson's team is already hard at work trying to chip away at these riddles by looking for viruses in sea stars from across six continents.

Top header image: Jay Wilson, Flickr