A decade after sea star wasting disease arrived in Sitka Sound, researchers are investigating the relationship between sea urchins, kelp forests and sunflower stars.
Scientists still don’t know much about the disease, which causes several species of sea stars, such as sunflower stars, to lose their limbs before dissolving.
“Sea star” is the name marine scientists now use with reference to the five-limbed marine invertebrate instead of the common term “starfish,” because it is not actually a fish.
Around Sitka, sea star wasting disease is responsible for the loss of sunflower stars, which are a key predator on sea urchins. If left uncontrolled, sea urchins will destroy kelp forest ecosystems.
Kelp forests promote biodiversity, create fish habitat — including a place for herring to lay eggs — and buffer waves.
“In a lot of areas, because of patchy otter populations, sunflower stars are the main predator,” said Nikita Sridhar, a Ph.D. candidate at University of California, Santa Cruz.
Sridhar is spending her third summer in Sitka conducting research on sunflower stars, sea urchins and kelp forests.
In the absence of sunflower stars, kelp forests have given way to “urchin barren,” as the areas are called after sea urchins have eaten away the kelp forests.
Sridhar’s research has worked at understanding the impact sunflower stars have on urchins, not just as a predator but as a deterrent to urchin proliferation.
“We’re looking at how the sunflower stars can change urchin grazing behavior — if the presence of a sunflower star scares an urchin into eating less kelp,” Sridhar told the Sitka Sentinel. “We have these big tanks and we pop some kelp in there and urchins, and in some of the tanks, we have sea stars. We’re trying to see how much kelp the urchins eat when the sea stars are present.”
She said that she’s also working with different kinds of sea urchins: ones from healthy kelp forests and ones from urchin barrens.
“If you have an urchin from a barren ... it might be really hungry and might care less that there’s a predator there,” she said, adding that urchins from barrens are much different from urchins living in healthy kelp forests.
“They seem like entirely different animals,” she said. “Their behavior is different but also visually, the kelp forest urchins’ spines are stronger and they clamp down on the rocks better.”
Sridhar’s research this summer builds off of her previous work in Sitka, including experiments last summer, when she observed differences in urchin behavior based on whether a sunflower star was in a cage or free to wander the tank.
“I was trying to see if the activity level of the sea star has an effect on the resulting urchin behavior,” she said. “We’re still looking at that behavior, but it looks like even a caged sunflower star can change the amount of kelp a sea urchin eats.”
All this work attempts to understand the effect sunflower stars have on kelp forest ecosystems.
“When you lose something … that’s when you realize how important they are for maintaining the balance,” Sridhar said.
Part of the hope of this research is that reintroducing sunflower stars could help rehabilitate kelp forests in the future. But that outcome appears to be a long way away.
“Because of sea star wasting disease, there are a lot of concerns about reintroducing sunflower stars,” Sridhar said.
Even so, Sridhar said some labs are trying to raise sunflower stars, and that the field of research on kelp restoration — seeding kelp forests and culling urchin populations — has grown in recent years.
Sitka, too, is a unique place to conduct research. Despite dwindling populations in Sitka Sound, where sunflower stars used to be common, the sea star populations remain steady in nearby waters.
“On the more exposed sides and on the Outer Coast, people have been seeing sun stars,” Sridhar said. “The populations aren’t decimated yet.”
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