A 15-year period ending in 2020 that included a marine heat wave and a sea star wasting disease epidemic saw major changes in the groups of organisms that live along the rocky shores of the Pacific Northwest.
The study by College of Science researchers, involving four capes in Oregon and California, suggests these communities of species may have low resilience to climate change. Findings were published Monday in Nature Ecology & Evolution.
Researchers learned that sessile invertebrates — those that stay in one place, such as mussels and barnacles — became more abundant during the study period, while seaweed species like kelps declined.
“These changes occurred after the loss of adult ochre sea stars due to an epidemic of sea star wasting disease and during a three-year marine heatwave when water temperatures were extremely warm,” said Zechariah Meunier, a doctoral graduate of the OSU College of Science and the lead author on the paper. “Sea stars are like the wolves of rocky shores because they normally eat enough mussels and barnacles to prevent these invertebrates from dominating the lower elevation areas. And many kelps did not survive the thermal stress during the heat wave.”
Of further concern to the scientists: When the epidemic ended and ocean temperatures cooled, the rocky shore communities did not return to their baseline conditions. That suggests the communities have low resilience to changes in both temperature and predator numbers.
“Diminishing resilience may lead to degraded rocky shore communities under future climate conditions,” said Meunier, who along with OSU professors Sally Hacker and Bruce Menge looked at 13 sites spread among Oregon’s Cape Foulweather, Cape Perpetua and Cape Blanco and California’s Cape Mendocino. “And a warming climate will make restoring baseline conditions more difficult – regime shifts to degraded states are likely to last longer and put community structure and ecosystem function at risk.”
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