Mobs of urchins butcher sea stars: In the lab, the spiny creatures turn their predators into prey

摘要

Sea urchins are underwater lawn mowers, their unabating appetites for kelp capable of altering whole nearshore ecosystems. But the spiny invertebrates will also sink their teeth into something a bit more challenging-and dangerous - new research suggests. In a first, scientists discovered urchins attacking and eating sea stars in a lab. The observations flip a classic predator-prey script, marine behavioral ecologist Jeff Clements and colleagues report in the June Ethology. But it's still unknown if this oddity of captive urchins extends to the wild. In 2018, the team was studying common sun stars (Crossaster papposus) at the Kristineberg Marine Research Station in Fiskebaeckskil, Sweden. At one point, Clements wanted to separate one of the sun stars for a short while and needed aquarium space. He placed the sea star in a tank containing about 80 green sea urchins (Strongylocentrotus droebachiensis). "I thought, OK, there's a bunch of sea urchins in there," recalls Clements, of Fisheries and Oceans Canada in Moncton. But since sun stars are predators of urchins, he figured the sun star would be safe.