Alaska has no shortage of marine predators – from orcas, to Steller sea lions, to salmon sharks. Over the past few years, researchers have identified a new, lesser-known predator that may play a key role in keeping Alaska’s kelp forests healthy.

Third-year graduate student Nikita Sridhar reaches deep into a tank in the basement lab of the Sitka Sound Science Center looking for what she calls an “underappreciated predator.” These creatures are such effective hunters that when they enter an area, it’s like you can hear the screams underwater,” Sridhar says. “Everyone’s just trying to flee the scene.” 

Sridhar wrestles the creature out of the tank and holds it up to the light – a dinner-plate-sized purple sea star. 

Sunflower stars, or Pycnopodia species, are the focus of Sridhar’s research this summer through her work with Professor Kristy Kroeker at University of California, Santa Cruz. Sridhar hopes to build on previous research to learn more about how sunflower stars could help protect coastal kelp forests. 

Sea stars may not intimidate us humans, but to a population of sea urchins, they’re a formidable predator.

“They basically throw their stomachs out, they lift up their arms, and then part of their stomach from the underside is thrown out,” Sridhar said. “And then they engulf the urchin.”

The sea star in her hands shows recent evidence of such grisly events — its stomach protrudes out of its body, and crushed urchin spines dot its many arms.

While unfortunate for the urchin, this kind of predation is good for the ecosystem. Urchins eat kelp, and too many urchins can decimate kelp forests that sequester carbon, which mitigates the effects of climate change, and provide homes to many critters.

“They’re like skyscrapers that create homes for all these different animals,” Sridhar said.

Keeping kelp forests healthy requires a balance of kelp-eating ‘grazers’, like urchins and abalone, and predators – like sea stars – who eat the grazers. 

“If you lose one part of this puzzle – for example, you lose an important predator – then you might have too many grazers,” Sridhar said.

That’s happened before – a decline in the population of sea otters, a well-known predator of urchins and other kelp-eating critters, led to the spread of “urchin barrens” along the Pacific coast, where urchins have mowed down entire kelp forests.

Now, researchers are trying to figure out if, and how, other predators such as sunflower stars could play a complementary role in protecting the kelp forests. 

Sunflower stars eat urchins, but Sridhar suspects that they may also affect urchin behavior in other ways. In her work this summer, she is trying to figure out if the mere presence of a sea star can cause urchins to eat less kelp.

“Just sensing this predator might lead to the urchins being scared into eating less kelp,” Sridhar said. “They might be investing their energy into running away from the predator or hiding in little crevices rather than just roaming on the seafloor, eating kelp as they please.”

In one experiment, Sridhar situates a caged sunflower star in the center of a tank full of urchins. She wants to see if the urchins move away from the cage, or eat less kelp, when they sense that a sea star is nearby. Out in Sitka Sound, her team is running similar experiments, tracking the path of a sunflower star and seeing how long it takes for urchins and abalone to return to those spots, or “whether that slime trail of a sea star is so strong that they’re too scared to come back, basically.”

If sunflower stars serve as vigilante kelp guardians, that’s exciting news for the kelp forests, especially if the sea star population rebounds. Sea star wasting disease has plagued the West Coast over the past decade, dissolving huge swathes of sea stars. Sunflower stars were hit especially hard by the epidemic.

Sridhar said they’ve seen more mature sunflower stars around Sitka Sound this summer than expected. That is, at least tentatively, cause for celebration.

“It’s exciting that we are seeing them this summer, and hopefully these populations persist through time,” Sridhar said. “We’ll see.”

Sridhar doesn’t have results back yet, but she’s excited to see how these sunflower stars might help protect kelp forests by creating what she cheerfully calls a “landscape of fear” for urchin populations. 

Kelp forest in Sitka Sound, being studied by researchers from UC Santa Cruz. (KCAW/Rachel Cassandra)

The kelp forests in Sitka Sound are rich ecosystems, full of animals that feed on seaweed. The Sitka Sound Science Center is hosting researchers from the University of California Santa Cruz who are examining these forests. I caught up with Umi Hoshijima, one of the researchers for the project.

Downloadable audio.

Umi Hoshijima picks me up in the University of California Santa Cruz’s bright orange inflatable boat. The researchers load it up with scuba gear and we pull out into Sitka Sound.

Umi Hoshijima, is a postdoctoral researcher with UC Santa Cruz. We’re looking for the kelp forest they’ve been researching. Hoshijima tells me about the variety of animals they’re studying: red and green sea urchins, the dusky turban snail and a few other snails, the pinto abalone, and a few limpets.

We pull up to a spot of water with bits of kelp showing on the surface. They confirm the location on their GPS. Then we anchor up. They suit up in their scuba gear and lean backwards into the water. They disappear under the waves. I just see air bubbling up to the surface every few seconds. Later, Hoshijima tells me how they were creating a snapshot of the underwater world just below the surface.

He says, “For every single one of these critters that we’re interested in, we’re going down with a set of calipers to get their size down to the nearest millimeter.” And they do this by placing a small square frame made of PVC every few feet on the ocean floor. Then they count and measure every single creature of interest within that square. It’s tedious work, but one of many things being done to understand the kelp forest.

He says, “What we’re trying to do with the survey is to spend our time looking really closely at small patches of the bottom, to get an idea of the little critters down there.”

Researcher Umi Hoshijima, heading to the kelp forest he’s studying. (KCAW/Rachel Cassandra)

This is the field component of the invertebrate research. It’s part of a larger project headed by researcher Kristy Kroeker through UC Santa Cruz and funded by the National Science foundation. The six researchers involved will look at invertebrates, as well as algae. There is also a lab component, where researchers take these animals and change the temperature and pH, or acidity, of their water. That way they can test how the creatures of the kelp forest would respond to changing ocean conditions. Hoshijima tells me what variables they’re measuring in the lab, “The amount of food they’re eating, how much they grow, and how much oxygen they’re breathing.”

And, Hoshijima adds, Kroeker’s team is especially interested in the impacts of ocean acidification and temperatures in the surface oceans rising. This is crucial for understanding the future of kelp forests on a warming planet.

He says, “We’re concerned that in the near future, a lot of the animals that we know and love in the kelp forest will actually have problems dealing with the more acidic environment. And that’s been shown to decrease the thickness of shells, for things like mussels and oysters and different clams, and that could make it easier for them to get chomped on. It’s actually even been shown in some species to impact the, impact the brains of fish. So it actually makes fish unable to have proper brain function in some ways.”

This year’s data will act as a kind of baseline for understanding changes in the kelp forest. The project has funding for five years of research.

Hoshijima says that means is that they can really spend the time to dig deep into the into the kelp forest.

With all this scientific understanding, Hoshijima hopes the research could impact the world, especially concerning climate change. He says, “We need to have a better idea of how our coastlines could end up changing in the near future. And by sort of teasing apart how that could happen, we might be able to enact policy and change things in a way that we can protect our resources for the near future.”

Students in Kristy Kroeker’s Marine Ecology Field Quarter spend part of the 20-unit class underwater. (UC Santa Cruz photo)

Undergraduate students from University of California Santa Cruz have been participating in a month-long marine ecology field course this February. Students Michael Langhans, Tamara Russell, and Clara Zeder talk about their experience diving in Sitka waters. They were joined by their instructor, ecologist Kristy Kroeker.

The students will present their research projects at 5:30 p.m., Friday March 2nd, at Sitka Public Library.

Downloadable audio.

In addition to diving, UC Santa Cruz students spend time studying the intertidal zone, and working in a lab. (UC Santa Cruz photo)

Downloadable audio.

Kristy Kroeker (Photo by C. Lagattuta)

Biologist Kristy Kroeker, an assistant professor of ecology and evolutionary biology at University of California, Santa Cruz (UCSC), has returned to Sitka for a month of research. She’s conducting lab and field studies on the impacts of ocean acidification to kelp forest communities at high latitudes. Among UCSC faculty, Kroeker was chosen as a “Climate Action Champion” to study the effects of climate change on human health.

Lauren Bell, research biologist at the Sitka Sound Science Center, talks her plans to pursue a PhD at UCSC this fall. She’ll be researching the impacts of ocean acidification on algal species.