Some comb jellies cannibalize their young when food is scarce

Adults chow down on their larvae to survive the winter

Mnemiopsis ledyi

Adult warty comb jellies (Mnemiopsis ledyi, pictured) feast on their young after large summer population booms deplete their food, a new study finds. Cannibalism may help the animals last through the winter when there’s little to eat.  

Bruno C. Vellutini/Wikimedia Commons (CC BY-SA 3.0)

Some jellies go ballistic when their prey disappears — cannibalistic that is.

Warty comb jellies, native to the western Atlantic Ocean, invaded Eurasian waters in the 1980s. The jellies have since flourished, cycling through population booms during summer when prey is abundant and busts in fall and winter when it’s not. Now a study finds that to persist when food is scarce, adult jellies eat their young.

Understanding how a “brainless, fragile animal” conquers new environments could reveal new ways to control the invasive species, says Jamileh Javidpour, a marine ecologist at the University of Southern Denmark in Odense.

Javidpour and her colleagues collected adult and larval comb jellies (Mnemiopsis leidyi) from Kiel Fjord — an inlet of the Baltic Sea east of Germany — in August and September of 2008, before and after the jelly population collapsed. As the adults’ preferred food source, small crustaceans called copepods, plummeted at the end of August, young comb jellies also began to disappear. By the end of the collapse, adults made up the bulk of the population.

Juvenile comb jellies
Juvenile comb jellies (indicated with red arrows) can be seen inside the auricles of an adult collected from Kiel Fjord in 2008. Jellies use their auricles to help draw in prey.Jamileh Javidpour

Back in the lab, the researchers chemically labelled larvae with a rare type, or isotope, of nitrogen, and placed the young jellies with starved adults. After 36 hours, those adults had higher levels of the isotope than adults fed a normal diet, a sign that the animals consumed the larvae, the team reports May 7 in Communications Biology.

Because larvae can’t survive the cold winters, the study suggests that this comb jelly species ramps up reproduction in late summer — when it might otherwise be counterproductive — in order to feast on its young and bulk up before winter (SN: 12/12/13).

“We thought that it was self-inflicting harm,” says coauthor Thomas Larsen, a biologist at the Max Planck Institute for the Science of Human History in Jena, Germany. But it seems the jellies are “building up resources for the winter.”

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