This Sea Slug Has a Crafty Way of Getting Super-Sized Meals

These colorful creatures prefer to feast on prey that has just eaten

Wilfred Hdez/Wikimedia Commons

With their dazzling colors and intricate patterns, nudibranchs are among the world’s most glamorous marine creatures. But as Steph Yin reports for the New York Times, the beautiful nudibranchs, who are commonly called sea slugs, may also be a cunning predator with a crafty way of getting a super-sized meal: feasting on prey that has just eaten.

A team of researchers from Britain and Italy set out to study the snacking habits of the Cratena peregrina, a species of nudibranch that is common to the Mediterranean. In the wild, these slugs are known to feed on hydroids, an invertebrate marine organism. Scientists gave 25 captive nudibranchs four different mesh bags: one had nothing in it, the second held shrimp brine, the third a hydroid, and the fourth a hydroid that had eaten shrimp brine.

Fourteen of the slugs made a beeline for the hydroid that had been fed, according to a study published recently in Biology Letters. “This supports the explanation that C. peregrina is an opportunistic predator that uses the hydroid as a means of obtaining prey from the water column,” the authors write. “A feeding [hydroid], having just captured or engulfed fresh prey, would constitute a more rewarding prey type—in terms of increased energy content—for the nudibranch.”

As Mindy Weisberger points out at Live Science, certain species are known to steal prey from other predators, a behavior known as “kleptoparasitism.” But the nudibranchs were doing something that had never been observed before: stealing prey by eating the original predator. Researchers dubbed this sneaky method of getting extra sustenance “kelptopredation.”

There are some limitations to the experiment, notes Ryan F. Mandelbaum of Gizmodo. For one thing, the study is based on a relatively small number of trials conducted in a lab, and therefore does not necessarily reflect nudibranch behavior in the wild. In an interview with Gizmodo, James Newcomb, a biology professor at New England College, offered another possible explanation for why the nudibranchs were selectively choosing fed hydroids: the hydroids had “expended their stinging cells to capture prey and thus could not use them on the nudibranch.”

Even so, the study is intriguing, and could possibly shake up our “predator-eats-prey” view of the food chain. When it comes to the nudibranch—and possibly other invertebrates, according to the authors of the study—something more complex may be going on.