Sea Star Wasting Disease (SSWD) has decimated sea star populations around the world. Since the epidemic of dead, dissolving sea stars was discovered around 2013, scientists have been trying to figure out the cause of the disease.
Researchers now think one cause may be that the sea stars cannot get enough oxygen. The animals don’t have lungs, but instead take in oxygen from the water using skin gills all over their bodies, called papulae. Bacteria naturally live on the surface of the skin. When there are changes in the ocean environment that produce a lot of organic matter, these bacteria multiply. As the bacteria consume the organic matter, they deplete the water of oxygen. When there’s not enough oxygen, the sea stars can’t breathe. This low oxygen environment leads to the symptoms of SSWD: dissolving, color loss and limb twisting.
There are many reasons for high quantities of organic matter in the ocean. Climate and other human activities are major ones.