Scientists in a San Juan Island laboratory in Washington state have successfully raised sunflower sea stars, or starfish, in captivity for the first time, in an effort to help save these charismatic ocean creatures from extinction.
Sunflower sea stars, whose colours vary widely, can grow as big as a bicycle wheel and have about 20 legs. They were once abundant in coastal waters from Alaska to Mexico, but since 2013, nearly 6 billion of these now critically endangered animals have died from a gruesome wasting disease linked to warming seas. Populations have plummeted by more than 90%.
As key predators, sunflower sea stars are vital in maintaining a diverse ocean ecosystem, said Jason Hodin, a marine biologist who is leading the research at Friday Harbor Laboratories on San Juan Island, the marine field station for the University of Washington. “These top predators actually help structure the ecosystem,” he said. “And when you remove them it often turns [habitats] into much more simplified and less diverse ecosystems.”
This has been starkly felt in California, said Hodin, where the absence of the starfish has coincided with the disappearance of kelp forests. The loss of the key predator has allowed a boom in populations of purple urchins, which devour kelp. It’s extremely concerning, said Hodin, because kelp forests are “the tropical rainforest of the oceans”. Kelp absorbs large amounts of carbon, purifies water and provides a vital habitat for marine creatures.
Hodin, a larval biologist, began the project in 2019 when the Nature Conservancy (TNC), an environmental charity, approached him with funding. Walter Heady, a coastal marine ecologist at TNC, said: “When we started this work with Dr Hodin’s team, we weren’t even sure if captive rearing was possible for this animal.”
Very little is known about the sea stars’ life cycle, partly because the larvae are so tiny that they are very hard to monitor or even locate in the wild, but also because “it’s not a commercially important species”, said Heady.
The first aim, said Hodin, was to get a better picture of the sea stars’ biology “to understand how the species might recover in the wild”. Through trial and error, Hodin and his team managed to rear sea stars from the larval stage in the laboratory. From a spawning in November 2019 they now have 12 juvenile sea stars. Another spawning in January 2021 has resulted in tens of thousands of larvae, which Hodin says are growing faster and better than the first batch.
The researchers have discovered that the larvae are able to survive warmer temperatures than those in their usual habitat, raising hopes that the species could be well adapted for anticipated water temperature rises resulting from the climate crisis.
The next stage in the project is to compile what Hodin calls a “cook book” – an instruction manual for how to raise sea stars on a large scale. The ultimate aim is to understand if these laboratory-reared starfish can be moved back to the ocean.
This will be challenging and requires regulatory approvals – the species’ range spans three countries. But Hodin hopes eventually to undertake controlled local tests to better understand the ecological consequences of such reintroductions.
Chris Mah, a Smithsonian researcher and sea star expert who is not involved in the work, said: “This [research] is the first step towards understanding how to help recover these populations, but it’s not a solution.
“It’s more than just one species,” he warned. “There’s an environment there that needs to be studied and we need to figure out what caused the problem.”
While sea star wasting disease has abated, scientific knowledge about the disease’s causes, and the link to warming oceans, is limited.
Hodin remains optimistic. “Our eyes are on the prize [of reintroduction],” he said, but the success of the project does not hinge on it. He hopes the attention on sunflower sea stars can help communicate the need to protect marine ecosystems. “We need to start thinking about the impacts we have on the wild in a broader context,” he said.