Urchin mobs team up to butcher sea stars that prey on them

The spiny invertebrates pin the sea stars’ arms in an overwhelming predator-prey role reversal

photo of a red/pink sea star

This common sun star (Crossaster papposus) was found mangled by dozens of ravenous sea urchins in an aquarium, reversing a classic predator-prey relationship.

Jeff Clements

Sea urchins are underwater lawnmowers, their unabating, vegetarian appetites capable of altering whole nearshore ecosystems.