The baby sea star looked like a strange gray flower, tucked in the dark purple “y” of an adult sea star’s arms
A crowd of people crouched in the sand near the rocks for a closer look. They were volunteers with a sea star monitoring project in Oswald West State Park on the North Coast. For the last hour, they had been hunting among three particular rocks, looking for sea stars.
The site is one of many that inform coastwide efforts to understand how and where the mysterious wasting disease that struck in 2013 and decimated sea star populations continues to impact the animals.
In recent years, citizen scientists and researchers have seen encouraging, if uneven, signs of recovery among ochre sea star populations along the Oregon Coast. The baby sea star at Oswald West is one such sign.
But a new study out of Oregon State University asks a critical question: How much can one community take? For organisms that live in the dynamic rocky intertidal areas off Oregon and Northern California, the answer might be: Only so much.
The new study examines a 15-year period that ended in 2020, a period that included a marine heat wave as well as the sea star wasting disease epidemic. During that time, researchers saw major changes in the intertidal communities of the Pacific Northwest that didn’t reverse even as conditions like water temperature improved.
In several cases, there were complete regime shifts, a rapid changeover of what organisms were present among the rocks, suggesting some of these communities may not be as resilient as expected in the face of climate change.
Unprecedented stressors
The researchers say pollution and climate change, in combination, mean marine ecosystems are experiencing unprecedented stressors like the heat wave and sea star wasting disease. Add to the list harmful algal blooms, low-oxygen areas and ocean acidification. These stressors and the conditions they create or exacerbate can damage habitat, while some areas might start seeing less diversity in species.
Kelp faltered in the marine heat wave that began in 2014. Around the same time, sea stars literally melted away, stricken by the mysterious wasting disease. At some sites examined in the study, other species were ready to flourish as predators like ochre sea stars disappeared — invertebrates like mussels and gooseneck barnacles.
Some sites flickered back-and-forth between different regimes, a phenomenon that Zechariah Meunier, a postdoctoral research associate at Oregon State University and the study’s lead author, said suggests “the system was close to its tipping point.”
Meunier and Oregon State 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.
What is especially concerning to them is the fact that, even with the return of cooler water, many of the affected communities they studied have not gone back to their baseline conditions.
Meunier said it’s a wake-up call.
Without a reversal, a system can get stuck in a positive feedback loop. For example, the conditions set rolling by the marine heat wave and sea star wasting disease opened a door for the expansion of mussel beds and the growth of very large mussels — mussels that could perhaps continue to avoid predation even after the ochre sea stars began to rebound.
“As mussels expand and cover rock, then they provide good habitat for smaller mussels that can settle into the mussel bed,” Meunier said. “Those mussels grow larger, expand the mussel bed, providing more habitat for more mussels — and so on.”
He noted that a warming climate will make restoring baseline conditions more difficult and “regime shifts to degraded states are likely to last longer and put community structure and ecosystem function at risk.”
Tom Calvanese, a fishery scientist with Oregon State and the lead for the Oregon Kelp Alliance, knows all about this type of cascade.
His work is focused in the area beyond the rocky shores, but involves some of the same organisms. Most significantly: kelp.
The decline of kelp forests has become a global concern. These forests provide key habitat to many species, including commercially important fish. The Oregon Kelp Alliance brings together a variety of stakeholders looking to document, preserve and restore the state’s kelp forests.
Kelp thrives in cold water. It suffered during the marine heat wave, but its decline was further exacerbated when sea star wasting disease tore through the sunflower sea star population.
Sunflower sea stars have not recovered in the same way as ochre sea stars. In their absence, sea urchins have multiplied. The urchins graze on kelp, turning once rich, ecologically diverse forests into barrens.
A status report by the alliance on Oregon’s kelp forests set to be released this summer estimates that the state lost more than two-thirds of its kelp forests between 2010 and 2022.
“That’s nearly 900 acres,” Calvanese said. “That’s a pretty significant change in a fairly short time.”
But it also wasn’t surprising. Calvanese, a former commercial urchin diver, saw the shift unfold with his own eyes.
The Oregon Kelp Alliance’s long-term goal is to move things back into balance. But in the short term, Calvanese said the hope is to maintain oases, places where wild kelp still thrives despite conditions elsewhere and where a certain amount of genetic diversity can be preserved — “hanging on to what we have,” Calvanese explained, “while we restore what we’ve lost.”
Essentially, he wants to buy the kelp time to adapt to a changing ocean.
Conservation approaches
Over the last few years, the Oregon Kelp Alliance has piloted several approaches to protect the state’s kelp forests, including removing and destroying urchins. This year, the group landed $2.5 million from the National Oceanic and Atmospheric Administration for its Oregon Kelp Forest Protection and Restoration Initiative, which will see them deploy conservation approaches on a large scale.
Marine heat waves and sea star wasting — these were massive events. Once they started, there wasn’t anything humans could do to stop them.
Meunier sees his study in conversation with a larger body of research about and responses to environmental change.
There are other questions he wants to put to the data that informed his study, other ways to look at and understand the issues — more work to be done as the impacts of climate events and disease continue to unspool and ricochet.