A study by Oregon State University scientists has revealed significant changes in the communities of organisms living along the rocky shores of the Pacific Northwest over a 15-year period ending in 2020. The period, which included a marine heat wave and a sea star wasting disease epidemic, saw an increase in sessile invertebrates like mussels and barnacles, while seaweed species such as kelps declined. The findings, published in Nature Ecology & Evolution, suggest that these communities may have low resilience to climate change.
The researchers studied 13 sites across four capes in Oregon and California, including Cape Foulweather, Cape Perpetua, Cape Blanco, and Cape Mendocino. “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, the lead author and a doctoral graduate of the OSU College of Science. “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.”
Low Resilience to Changes in Temperature and Predator Numbers
The scientists expressed concern that even after the epidemic ended and ocean temperatures cooled, the rocky shore communities did not return to their baseline conditions. This suggests that 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,” Meunier said. “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.”
The Importance of Healthy Marine Ecosystems
OSU professors Sally Hacker and Bruce Menge, who have been studying Northwest coastal ecosystems for decades, emphasize the importance of healthy marine ecosystems. The ocean and the species that inhabit it are critical to the proper functioning of the planet, supplying half of the oxygen humans breathe and annually absorbing one-quarter of the carbon dioxide people emit into the atmosphere.
Climate change and pollution are forcing marine ecosystems to experience unprecedented stressors, including harmful algal blooms, ocean acidification, and hypoxia. These stressors often work in concert and exacerbate one another, resulting in damage to marine habitats or species diversity loss. When stressors are especially severe, they can lead to habitat transitions from one state to another, known as a regime shift.
While sunflower stars have not recovered, adult ochre sea stars on rocky shores are growing in size and number to what was measured before the disease epidemic. The researchers express hope that the sea stars will be able to limit the expansion of barnacles and mussels in the future.
The study, funded by the National Science Foundation, highlights the complex interactions between climate change, disease, and ecosystem dynamics in the Pacific Northwest’s rocky shores. As the world continues to grapple with the impacts of a changing climate, understanding and mitigating these effects on marine ecosystems will be crucial for maintaining their health and resilience.
