Sea slugs: the pirates of the ocean

Researchers have discovered a new strategy for obtaining food in the wild: sea slugs  wait until their prey has eaten a meal, and then they pounce.

The researchers named the cunning strategy kleptopredation, and they think it may allow the colorful sea slugs, called nudibranchs, to obtain the calories they need without over-hunting their food sources. The nudibranches feed on hydroid colonies, which are super-organisms similar to corals that are comprised of individual polyps. The nudibranchs preferentially ate polyps that had themselves just eaten zooplankton. Over half of the nudibranchs’ diet was zooplankton that their prey had eaten.

Dr. Trevor Willis of the University of Portsmouth, the study’s lead researcher, thinks the behavior might have evolved to allow the nudibranchs to feed on the hydroid colonies without depleting them.

“We suspect it does this [as a] balancing act,” he said. “I imagine that it started with a nudibranch that happened to increase its foraging rate when plankton were captured, and as a consequence experienced greater reproductive success. Perhaps a gene that influenced this behavior was thus perpetuated.”

This is the first instance of such behavior that has been discovered, and it’s unclear how widespread it might be. Dr. Willis said examples of kleptopredation may be found elsewhere in the animal kingdom.

“I would be very surprised if this phenomenon was not discovered to occur in other specialized predator-prey pairings,” he said. “I think there are likely to be many trophic linkages waiting to be discovered. Underwater science in general lags behind somewhat just because working under the waves is so much more difficult.”

“There are so many discoveries to be made in the sea,” he said, “and often it just a matter of looking to find new and wonderful species and interactions between them.”




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