That Time a Mushroom Coral Ate a Sea Slug

Researchers observed the rare event off the coast of Thailand

Mushroom Coral Eating Sea Slug 1
Researchers witnessed this coral slowly slurp up a sea slug back in December of 2014. Mehrotra et al.

Sometimes mushroom corals get hungry. And, apparently, to quell that hunger, sometimes they eat sea slugs. On December 22, 2014, researchers working off of Koh Tao Island in Thailand were quite surprised to see a mushroom coral (Pleuractis paumotensis) slurp up an unsuspecting sea slug (Plakobranchus sp.), as Jason Bittle reports for Hakai magazine. 

The dive team observed the coral for about 20 minutes, and a full account with underwater images of the event appears in this month’s issue of the journal Coral Reefs. Though one might typically think of corals as benign, “incidental observations like this one can clarify the role of corals as predators, and which prey they can consume,” the researchers write.

Mushroom corals have been known to occasionally eat jellyfish and sea salps (gelatinous, floating jellyfish-like animals) but algae still makes up most of the corals’ diet. When they do eat bigger things, the coral zaps prey foolish enough to venture too close to its folds with miniscule tentacles and then maneuvers the food into its large mouth or rather one of its mouths, as Shaunacy Ferro notes over at Mental Floss. Some mushroom corals have more than one mouth, but this coral just had the one. (Bittle appropriately likens mushroom corals to the Sarlacc creatures of Star Wars.)

No one’s ever seen a mushroom coral eat a sea slug. But it’s not too surprising that they might be on the menu. Sea slugs share some characteristics with salps, but they are thus far, the most complex organism on the mushroom coral menu, as Rahul Mehrotra, one of the divers and a paper co-author told Bittle.

Though the slug hadn’t been completely swallowed when the team left the site, its survival odds are slim.

The mushroom coral eventually began to swallow the sea slug. Mehrotra et al.
Research divers watched for 20 minutes as a sea slug disappeared into this mushroom coral's mouth. Mehrotra et al.

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