In 2013, sea stars began dying along the North America’s West Coast, across a vast region from Baja California up to the Gulf of Alaska. To date, nearly six billion sunflower stars have died from sea star wasting disease. With the help of sophisticated new technology and RNA sequencing, scientists have finally figured out the cause: Vibrio pectenicida, a type of saltwater-loving bacteria that spreads fast in warmer waters. For bioGraphic, Craig Welch reports on this research in an illuminating, accessible science story, accompanied by stunning in-lab and underwater photography and video.
The changes Downie has seen on the seafloor are nearly as troubling as those in his bank account. Voracious purple urchins, a species for which there is no market, have mowed down lush bull kelp (Nereocystis luetkeana); along a 350-kilometer (217-mile) stretch of coast in Sonoma and Mendocino counties, 90 percent of kelp died. That’s left no food for red abalone, causing a US $44 million recreational abalone dive fishery to close. Baby rockfish, which typically hide within long, waving kelp strands, have also dwindled, as have many other species. Much of the region now resembles underwater clearcuts—a patchwork of overgrazed seafloor that scientists call “urchin barrens.”
In 2020, after prior attempts failed, The Nature Conservancy decided to finance one more effort to determine the cause of death. With additional support from the Hakai Institute, the organization agreed to pay for Gehman’s research. Soon after, she received her first shipment of healthy stars from Puget Sound. Her team slowly exposed them to a slew of contaminants: the tanks of sick and dying stars; seawater housing ill stars; ground-up flesh from dead stars; sick stars’ internal fluids. In each case, the healthy stars died, usually within a week. When the team heated ground-up tissue and bodily fluids from sick stars to kill pathogens before injecting the mixture into healthy stars, none got sick. That confirmed that a microorganism, and not heat alone, was to blame. But what kind of organism?
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