Some of you may have heard that the sea stars on the West Coast of North America are going through a mysterious disease. What you might not know is that this could be the largest die-off in the known history of the planet. Marine or terrestrial. It’s causing millions of sea stars, urchins, and sea cucumbers to literally disintegrate into white mush piles in the intertidal shores from Mexico to Alaska.
Sea Star Wasting Syndrome, as it is now known, first manifests as lesions on the outer skin layer, then the tissue starts to decay around those lesions. The body then deteriorates until the appendages dissociate from the body. It fragments and true to name, wastes away.
This phenomenon was first spotted in 2013 in Washington in ochre stars (Pisaster ochraceus), but has since been recorded throughout the coast line. Scientists are honing in on the cause for this, but the exact variables are still unknown. What is known is that a densovirus, commonly found in the ocean is associated with the disease. However, this virus can be found in preserved sea stars from decades before. A paper published this year has found that warming sea temperatures has exacerbated this disease. Potentially pairing with the virus to cause the devastation.
Areas where you may have seen 200-400 stars, you can now find one or two. Yet, the population is slowly on the rise again. An individual sea star can have thousands of larvae in one reproductive event, so hope for a comeback is not lost. However, the intertidal community is already changing. Sea stars are known as “keystone predators”. Their presence or absence makes a huge difference in the entire make-up of the ecosystem. They feed on mussels, keeping the mussel population numbers in check. Without the predators, the mussels are taking over the coasts, outcompeting other species such as barnacles, limpets, and algae, to name a few. So this die-off has a far reaching affect.
Sea urchins have also been affected by the disease, though not as harshly. And because of the lack of sea stars, their numbers have also grown. Urchins eat kelp, so their increasing number is having a drastic effect on kelp forests. If you have ever dived through a kelp forest, you know that they are home to thousands of species; they act as nurseries for juvenile fish and protection from larger fish and invertebrate species. Many things depend on kelp to survive, whether for protection or food. They are a defining habitat for the eastern Pacific, and the loss of this habitat could have disastrous effects.
Universities, Aquariums, and Museums across the coast are monitoring the effects of this disease on the sea stars and the entire ecosystem. There is research being done on transmission of the virus between sea stars and whether it affects juveniles or larvae. No one yet knows why some areas were affected before others, or whether the charismatic stars will recover, but citizen scientists have been brought in from all along the three countries to track the progress. So, next time you’re diving off the west coast of North America, take note of the number and condition of the species you see. You might be able to help bring some answers to this baffling situation.
‘Sea Star Wasting Syndrome’ was written by Roya