You may not think of starfish as predators, but they are. Especially the sunflower sea star, a 24-limbed, gorgeously-colored, quick-moving (for a sea star), urchin-eating machine. Sunflower sea stars (scientists prefer this nomenclature over “starfish”) can grow to almost a meter across. It used to haunt the waters off the west coast of North America in huge numbers.
But recent population decline has allowed purple urchins to breed unchecked. Those little guys are, in turn, mowing down the kelp forests that serve as a cornerstone habitat in those waters.
What to do?
A team of researchers thinks it has the answer. In a paper published in the Proceedings of the Royal Society B, authors A.W.E. Galloway, S.A. Gravem, and others studied what might happen if scientists re-introduced large numbers of sunflower sea stars into their native habitat.
Sunflower sea star, center, in an intertidal area. Photo: Jerry Kobalenko
Disease destroyed many of the giant stars
Encouragingly, they found that “even small [sunflower sea star] recoveries could generally lead to lower densities of sea urchins that are consistent with kelp-urchin coexistence.”
That’s because sunflower sea stars prefer snacking on purple urchins above all other foods. The scientists collected 24 healthy, wild sunflower sea stars and subjected them to tests that amounted to “Hey, what would you like to eat today?”
What they found is that sunflower sea stars prefer urchins that have been feeding on kelp to starved urchins (good news for kelp!) and will go out of their way to eat an urchin if one is around (bad news for urchins).
They also ran population models to determine how a reintroduction might impact urchin numbers.
In a word: look out, urchins.
Sunflower sea stars once prowled the waters from Baja to Alaska, feasting on urchins and anything else they could wrap their 24 arms around. But a wasting disease struck the species in 2013 and wreaked havoc, destroying as much as 80% of the population. In some areas, the sunflower sea star vanished altogether.
The importance of predators in any ecosystem is well-studied. So researchers had a hunch that purple urchins’ subsequent decimation of kelp forests was directly related to the sunflower sea star population crash. In 2019, scientists from the University of Washington’s Friday Harbor Laboratories began a Nature Conservancy-funded program to breed and raise sunflower sea stars to adulthood — something nobody had ever attempted.
The kelp forests off the West Coast are dying, and with their decline, an entire ecosystem of marine plants and animals is at risk. A large starfish with an appetite for sea urchins could come to the rescue. https://t.co/GA5Na4yWIq
— The New York Times (@nytimes) March 6, 2023
Until now, it was all just theory. The recent paper provides the first solid evidence that the sunflower sea star can control purple sea urchin populations.
Best of all, Galloway told the New York Times, “the restoration of sea stars…works without human intervention after it gets started.”
