The Ochre Sea Star (Pisaster ochraceus) has arrived on Kodiak Island. Ochre sea stars are common in the Pacific Northwest, but the species is slowly expanding its range further north into the cooler waters of the Gulf of Alaska. Brenda Konar, professor of marine biology at the University of Alaska Fairbanks, says she thinks Kodiak is near the end of its range.
Ochre stars inhabit the Gulf of Alaska and are now common in Prince William Sound. What does their northward migration mean? Scientists think they could be moving further north due to warmer water temperatures in the North Pacific. Ochres stars are incredibly hardy and adaptive, allowing them to inhabit exposed rocky beaches from Baja California to Prince William Sound. Ochre stars can wedge their bodies into rocky crevices on wind-swept coasts, so they don’t get washed away during a storm.
Ochre sea stars reign near the top of their food chain. Seagulls can eat young sea stars, and sea otters eat sea stars of any size, but they have no other predators. Ochre stars eat a wide variety of prey, including mussels, limpets, sea urchins, snails, chitons, and barnacles.
Ochre stars are important in the intertidal communities they inhabit, and scientists consider them a keystone species because their presence affects the intertidal community. They are voracious predators and seem to prefer mussels. Mussels are superior competitors for space on rocky coasts, but when Ochre stars wipe out a group of mussels, other species move in to colonize the area. Since mussels tolerate desiccation better than Ochre stars, mussels can proliferate in the upper intertidal zone. In contrast, the presence of Ochre stars in the lower intertidal eliminates large mussel beds and allows other species to flourish.
Ochre stars begin breeding at age five. They broadcast their eggs and sperm into the water, and fertilization occurs externally. The larvae float in the ocean for a few months and then settle onto the bottom, where they take on the sea star shape. Scientists believe it is during this floating larval stage when the sea stars expand their range. Ochre stars are the most long-lived species of sea star and can live twenty to thirty-five years.
A massive die-off of sea stars on the west coast of the US, including Alaska, began in 2013. Biologists believe the die-off was caused by a virus that flourished during a cycle of hot water temperatures in the North Pacific. Most sea star species are beginning to recover, and the Ochre star seems to be one of the more resilient species.
Will we see more Ochre stars on Kodiak Island, and if so, what will their presence do to the intertidal communities? In Uyak Bay on Kodiak, where I live, mussels flourish in certain areas, but a large population of sea otters has decimated many of the bivalves, sea urchins, and crabs. If Ochre stars move into this area, will they survive the sea otters, and if so, how will they change the makeup of species in the intertidal zone? Only time will tell.
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Robin Barefield is the author of five Alaska wilderness mystery novels: Big Game, Murder Over Kodiak, The Fisherman’s Daughter, Karluk Bones, and Massacre at Bear Creek Lodge. She is also the author of the non-fiction book Kodiak Island Wildlife. Sign up below to subscribe to her free monthly newsletter on true crime and mystery in Alaska, and listen to her podcast, Murder and Mystery in the Last Frontier.
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