Colorful sea stars have traditionally been a bright spot for tidepool visitors – but in recent years, these charismatic stars have been dealt a heavy blow. Sea stars serve as keystone species in the ocean because, as predators, they keep populations of other animals in check, from mussels to sea urchins. The sea star uses tiny tube feet on its underside to walk along the ocean floor, and the suckers on the tube feet can help them latch onto and pry open their prey. The presence of sea stars can contribute to the presence of a lush kelp forest, which would otherwise get mowed down by sea urchins, or the diverse intertidal community of algae, barnacles, and other invertebrates that would otherwise be crowded out by mussels.
In 2013, a strange thing was discovered along the West Coast ranging from Mexico to British Colombia. Scientists found that millions of starfish were dying. A disease called sea star wasting syndrome afflicted these animals. In one of the greatest losses of these invertebrates in history, sea stars that were healthy and appeared to have nothing wrong with them suddenly became sick and started almost melting and breaking apart, turning into a slimy, gooey substance. Prior to the starfish turning squishy, they often formed visually striking lesions all over their bodies. Although the wasting disease has been evident since the 1970s, and previous die-offs have occurred in past decades, its destructive scale has never reached this magnitude (Miner 2018).
The massive sea star die-off was first observed in the ochre starfish (Pisaster ochraceus) in Washington. Next, leather stars, mottled stars, six-armed stars and sunflower stars soon followed in melting away by the wasting disease. At University of California, Santa Cruz, research is being done to determine the origins of sea star wasting disease, although it is proving difficult because suspected factors like warm water temperature and population density have not been identified as a “smoking gun” related to the disease. Researchers have found a virus associated with the disease, but its role in the epidemic is not conclusive. Research suggests that climate change, which can disrupt the ocean’s natural processes, is also a strong contributor to sea star wasting disease (Kohl 2016).
Although sea star populations have declined alarmingly in the last few years (by up to 99 percent in some southern California sites), recent reports show that their numbers are on the rise again where they were hardest hit. While this is cause for hope, the disease is still evident and spreading through the ocean, with the potential to dramatically alter the marine environment where sea stars live. Further research to understand the origins of the disease may help the recuperation process for sea star populations.
This story was written by Sarkis Kasparian for an internship with FISHBIO through the UC Santa Cruz Environmental Studies Department.