We all know and love the fascinating, 5-legged creature that inhabits the world’s oceans – the sea star. Although commonly known as the starfish, the sea star is not a fish at all – it is an invertebrate. Among our oceans live some 2,000 species of sea star. They thrive in habitats ranging from tropical regions to deep down on the cold sea floor. Recently, however, on the West coast, these creatures have not been so lucky. There is something plaguing the sea star and taking a severe toll on their population. Luckily, researchers are on the job, investigating what is taking the lives of millions of these keystone marine predators.
Sea Star Wasting Disease
The scene of the crime isn’t messy or jumbled – a solitary sea star skeleton, covered in white bacteria. The story begins and ends with one sea star. The killing begins as the tip of one of the sea star’s arms begins to curl up and cross over another arm, twisting up in a knot. This action causes a white lesion to appear within days. In little time, the arm with the lesion falls off, and the sickly sea star, lacking enough strength to grab hold of anything, topples over to its death. Eventually, the flesh disintegrates and all that is left is the skeleton covered in bacteria.
Since 2013, this phenomenon, which has claimed the lives of millions of sea stars up and down the West coast, from Alaska to Baja, California, has stumped scientists. They have termed the disease outbreak “wasting disease.” The disease has affected at least 20 sea star species, completely taking out more than 90 percent of some of the populations on the U.S. Pacific Coast.
The Cause of the Disease
Scientists have been wrapping their heads around what causes these sea stars to essentially melt into nothing. One explanation they came up with was that either pollution or the increasingly acidic oceans are weakening the sea star’s ability to tolerate the conditions. In 2014, microbiologists from Cornell were able to identify a virus that could be partially responsible for this horrendous outbreak. Just this past February, a PhD student and her colleagues in the ecology and evolutionary biology lab at Cornell published their results in Philosophical Transaction of the Royal Society B, giving evidence that the sea stars died faster when in warmer ocean water of the West coast in 2014. “The warmer water made the epidemic much more widespread and catastrophic,” says Drew Harvell, a professor of ecology and evolutionary biology at Cornell.
But scientists aren’t stopping there. They’re investigating what affect this dramatic loss of sea stars could have on the ecological community on the West coast. Sea stars are known keystone predators, which means that they play a crucial role in the way an ecosystem operates. Without them, the ecosystem would function much differently, or could even dissolve all together. On the rocky reefs of the Pacific Coast, sea stars keep various populations in check, consuming barnacles and other shelled sea creatures. The late Robert Paine, a great ecologist at the University of Washington, coined this term after the stone at the center of an arch that keep all the rest of the stones from falling down. Paine carried out decades of experiments where he removed sea stars off rocks on the northwest coast of Washington to see what happened when this top predator was absent. Sure enough, large populations of barnacles and black mussels took over the location from which the sea stars were removed.
Trying to Make a Comeback?
Despite the lack of sea stars on the West coast due to this disease, researchers have pinpointed some young ones trying to make a comeback and recover after being plagued by the disease. Unfortunately, many of these individuals grow to palm size, then eventually surrender to the disease, to weak to move on. The effect that this massive die off will have on the rocky reefs will depend on how well these sea stars are able to rebound. Researchers at the University of Califonria-Santa Barbara (UCSB) have photographed and measured, as well as taken DNA samples, from sea stars they were able to spot amongst hoards of mussels and limpets
Researchers are hoping that by taking DNA samples from the sea stars attempting to survive, they can get to the bottom of why so many of their siblings have fallen to the wayside. One thing the team didn’t think was a factor when they were taking account of the diseased sea stars up and down the coast was the water temperature. After they took a look at satellite imagery, they noticed that it had been one of the warmest winters in decades.
Once abundant sunflower sea stars are now a rare find off the coast of Washington around the San Juan Islands. It’s sad to think that this could continue in the future with climate predictions revealing warming conditions for the future.