In 2013, sea stars along the West Coast began to die en masse from a mysterious virus. Scientists called sea star wasting syndrome, as the disease came to be known, one of the greatest die-offs ever recorded. It was also a gruesome death, with sea stars ripping off their own limbs and melting into a puddle of goo. There is still no confirmed cause for the virus, but there have been breakthroughs along the way, like Smithsonian Institution scientists who recently discovered that the ochre sea star evolved genetic resistance to the virus, published last week in the Proceedings of National Academy of Sciences of the United States of America (PNAS).
Although Ocean Wise’s Howe Sound Research Group does not study genetics, the team and its long-term ecosystem surveys have been instrumental in studying sea star wasting syndrome. Senior Research Scientist Jeff Marliave had this to say about the recent study:
“The ochre stars (Pisaster ochraceus) showed very high mortality, greater than 80%, but still had large numbers left which must have allowed the genetic basis for adaptive response in short order. Our species of investigation, the sunflower sea star (Pycnopodia helianthoides) was the species that showed almost 90% mortality in 2013 and which has only slowly reappeared on the scene.
“We have always seen very young sunflower stars, most of them dropping out, but obviously some did survive, and no doubt their genetic makeup contributed to their differential survival. We are finally seeing small numbers of larger sub-adult sunflower stars and it is reassuring that high population levels are not completely necessary for an ecological effect to be evident.
“After the 2013 die-off, the green urchin population exploded in number, leading to a decline in kelp cover. Green urchins are a key prey item for sunflower stars, and a number of studies have demonstrated that green sea urchins will flee from sunflower stars. Just the smell of a sunflower star’s ‘body odour’ may be enough to make them run away. We now have two sites where it looks like the sunflower stars have herded the urchins up to a shallow depth, above the range of the sunflower stars. The kelp beds have rapidly bounced back at the depth range of those sunflower stars. This represents a sort of reversal of the trophic cascade that led to urchin barrens after the sunflower stars collapsed.”