Sea stars could play a key role in protecting threatened kelp forests, according to new research from University of Oregon and Oregon State University scientists.
The study, published Wednesday in Proceedings of the Royal Society B, found sunflower sea stars consume kelp-eating urchins at rates sufficient enough to maintain and potentially reset the health of kelp forests.
“What we saw suggests a clear link between the crash of sea stars, the explosion in sea urchin populations and the decline in kelp,” said Sarah Gravem, a research associate in Oregon State’s College of Science. “It also points to sea star recovery as a potential key tool for kelp forest recovery.”
Sunflower sea stars help keep sea urchin populations at healthy levels for kelp, but the sea star’s population has seen a dramatic decline. In 2020, the species was listed as critically endangered by the international Union for Conservation of Nature after suffering from sea star wasting syndrome, a marine wildlife epidemic that began in 2013, scientists said.
Since the outbreak, there are no signs of population recovery. No sunflower sea stars have been seen in Mexico since 2016, and few have been found in Oregon and California since 2018, scientists said.
While researchers thought the sea star decline caused an increase in urchin populations, the relationship between sea stars, urchins and kelp had not yet been quantified, scientists said.
“This study addresses that gap, and the findings are significant and somewhat surprising,” said principal investigator Aaron Galloway of the University of Oregon’s Oregon Institute of Marine Biology. “We found that these stars are eager consumers of purple urchins and, most importantly, they even eat the nutritionally poor, starving ‘zombie’ urchins.”
Overgrazing by sea urchins and climate change currently threaten kelp — a large algae with significant ecological and economic importance worldwide.
Kelp occupy nearly 50% of the world’s marine ecoregions, forming large aquatic forests and providing essential habitat, food and refuge for many species, scientists said. It thrives in cold water, meaning climate change and a warming ocean pose a threat.
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Predators of purple sea urchins, like sea otters, don’t typically eat starving sea urchins from barrens, large underwater carpets of urchins that have eaten away their food supply, scientists said. These urchins can live in an emaciated state for years until the kelp grow back.
Sunflower sea stars eat about 0.68 sea urchins a day, and they will eat the starved urchins 21% faster than well-fed urchins in healthy kelp forests, according to the study.
“Eating less than one urchin per day may not sound like a lot, but we think there used to be over 5 billion sunflower sea stars,” Gravem said. “We used a model to show that the pre-disease densities of sea stars on the U.S. West Coast were usually more than enough to keep sea urchin numbers down and prevent barrens.”
The study’s authors, which included scientists from the University of Washington and Florida State University, are calling for active management and a coordinated sunflower sea star recovery.
Researchers have developed a “Roadmap to Species Recovery,” which includes the world’s first captive breeding program for sunflower sea stars and a pathway to reintroduction, scientists said.
Makenzie Elliott covers breaking news and public safety for The Register-Guard. Reach her at MElliott@gannett.com. Find her on Twitter at @makenzielliott.