These sea stars were nearly wiped out — but B.C. researchers say fiords provided refuge
Researchers say sea star wasting disease, whose exact cause is unknown, may be affected by water temperatures
B.C. researchers have found that the fiords of the Central Coast may be providing refuge for the critically endangered sunflower sea star, a discovery that could have implications for wider ecosystems at risk due to warming seas.
Nine out of 10 sea stars have been wiped out since 2013 due to sea star wasting disease, which has led to a mass death of the animals along North America's West Coast, from Alaska to Mexico. The sunflower sea star is listed as critically endangered by the International Union for Conservation of Nature.
While the exact cause of the disease is unknown, scientists say it's had major ripple effects, as sunflower sea stars eat sea urchins and perform an important role in keeping those populations in check. Without them, urchins have flourished and been able to eat kelp forests, which further destabilizes marine ecosystems.
Now, after years of diving along B.C.'s Central Coast, researchers have found many healthy adult colonies of sunflower sea stars in the fiords there.
Alyssa Gehman, a scientist with the Hakai Institute and an adjunct professor at the University of B.C., co-authored a paper on the findings. What they found, she said, is that while sea star wasting disease has been found in fiords and sea stars have died there, the mortality rate is far lower than elsewhere in the ocean.
Researchers suspect the difference has something to do with water temperature. In fiords — long, narrow, and deep inlets often found between high cliffs along the central and north coasts — the ocean tends to be cooler than elsewhere.
Gehman said the research team was first alerted to the large number of sunflower sea stars in fiords by Central Coast Indigenous Resource Alliance divers who were looking for rockfish — and the two groups ended up collaborating on the final research paper.
"When we looked at the oceanography ... we found that where the sea stars are, it's colder," Gehman told Darius Mahdavi, CBC's science specialist. "That's our next thing, is trying to figure out exactly what that temperature relationship is, and how that's working."
Changes in seasons
Jeff Sha, an aquarium biologist at the Vancouver Aquarium who wasn't involved in the study, said scientists have evidence that sea star wasting disease thrives in warmer water.
"The higher the temperature, the more likely the onset of the disease, and the harder it is for an infected sea star to come back from that," he said.
"As temperatures are rising along our coastlines ... we've had a couple of heat domes in the last decade, each of those events basically was another round of devastation for the population."
Gehman said in the fiords, Arctic outflow conditions create cold winds in the winters, cooling the water and making the environment higher in oxygen, which is good for sea stars.
"In the summer, when it's hot, there's glacial runoff that comes through," she said. "And it's so fascinating, but it creates essentially a little freshwater river on the surface of the fiord."
Sha said sea stars don't like fresh water, which means they'll go deeper and into the colder water.
"The researchers are hypothesizing that that's kind of what's giving them a little bit of a refuge away from the warmer temperature zone, and keeping them healthy from the wasting disease," he said.
Implications for recovery efforts
Sha said sunflower sea stars, in particular, are a ferocious predator for sea urchins — and without them, there's been devastating effects for other species.
"Sea urchin populations have boomed on our coast, causing a decline in our algae and our kelp forest, which then removes habitats for rockfish and all these beautiful animals that we have," the biologist said.
Gehman said some kelp forests along B.C.'s coast have been reduced to "urchin barrens," where all of the leafy portions of the kelp have been consumed by sea urchins.
The scientist said that, as researchers look to raise sunflower sea stars in the laboratory and put them back in the ocean, their work in the fiords could be important — though she acknowledged that climate change will continue to affect whether fiords can remain a "refuge habitat" for the species.
"There's hope that we could potentially raise stars that would be resistant to the disease," she said. "And this suggests that we need to pay attention to temperature when we're doing that work as well."
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With files from Darius Mahdavi