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

Nature can be brutish sometimes! Survival of the fittest!

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

"... We observed urchins preying on three separate sea stars, with one being substantially consumed by urchins within 24 hr. Urchins exhibited a direct mode of attack on sea stars by individually mounting and consuming the tips of the arms. Interestingly, we did not observe any conflict between individual urchins for attacking the sea star despite there being ≈80 starving urchins in the tank (and only 10–12 arms on the sea stars). Some sea stars did not attempt to escape urchin predation at all, while others attempted to escape by fleeing and lifting arms on top of the urchins. Given that sensory perception in sea stars is largely derived from the arm tips, we suggest that urchins directly attack and consume many sea star arm tips in an attempt to “pin” sea stars before consuming them. ..."

Urchin mobs team up to butcher sea stars that prey on them | Science News The spiny invertebrates pin the sea stars’ arms in an overwhelming predator-prey role reversal

Here is the link to the underlying research article:

“Urchin pinning”: Behavioural observations reveal how hungry urchins actively prey upon their sea star predators (public access)