All along North America’s West Coast, sea stars are vanishing. The colorful invertebrates are falling victim to one of the largest epidemics ever seen in the ocean: a mysterious plague known as sea star wasting disease. A new study by researchers in the lab of Professor of Biology Sarah Cohen delves into the dramatic decline this disease has caused in Leptasterias — also known as six-rayed sea stars — around San Francisco Bay. The research shows that the afflicted sea stars may have a lot to tell us about why wasting disease ravages some populations and leaves others relatively untouched.
Six-rayed stars are a crucial link in marine food chains, voraciously preying on animals like barnacles, snails and mussels and keeping their populations in check. With many sea star species in steep decline, the delicate tidepool ecosystems they occupy may be at risk, warns study lead author and SF State graduate student Noah Jaffe.
The team combined sea star counts from Jaffe’s fieldwork with pre-existing survey data from numerous sources that was compiled by co-author Renate Eberl, an SF State alum and a biology instructor at Santa Rosa Junior College. This allowed them to estimate Leptasterias populations at 46 sites along the California coast, both north and south of the Bay, as part of their investigation. They found that sea star numbers have declined dramatically in the area around San Francisco. Six-rayed sea stars at many of these beaches died out completely — in contrast, sea stars are still present farther south and abundant in tidepools farther north, even when the disease is present. The key to this difference may lie in ocean current patterns: the waters of the less-affected sites are cool and salty, while the water that flows south out of the Bay is “warmer, less salty and more variable. Those are all stressful things for these animals,” Jaffe explained. And that stress may be making them more susceptible to the unknown virus or bacteria that causes wasting disease.
The results of the research were published in PLOS One on Nov. 21.
Original post in the SF State Faculty/Staff Newsletter CampusMemo