Some comb jellies survive the winter by eating their young

2020-05-07

You wouldn’t want this creature as a parent. An invasive species of jellyfishlike animal in the Baltic Sea may survive harsh winters by consuming large numbers of its larvae, new research suggests.

Mnemiopsis leidyi—commonly known as the sea walnut (above), because of its shape—is native to the western North Atlantic Ocean. But it has proliferated in European waters in recent decades, likely after hitching rides in the ballast waters of cargo ships. In the western parts of the Baltic Sea, the species’ end-of-the-summer population booms ravage the base of the marine food web, including fish eggs, fish larvae, and small crustaceans. But the creatures need lots of food to bulk up for winter—and the largest source of sustenance at that point is their own offspring.

Field studies in a fjord near Denmark, including analyses of freshly caught comb jellies, found adults that had indeed consumed larvae of their species. And lab studies back up that finding, researchers report today in Communications Biology.

Cannibalism may help solve the mystery of why these creatures produce so many larvae in late summer even though they’d be unlikely to survive the upcoming winter. The team estimates that consuming large numbers of larvae at the end of the Baltic summer provides adults with an estimated 2 to 3 weeks of nourishment. That, in turn, leaves the adults with adequate reserves to survive 80 days at winter water temperatures without consuming any prey at all.

The details of the scheme’s energy balance aren’t yet fully understood, the researchers admit. Yes, it takes a lot of energy for adults to produce larvae that won’t survive the winter, they note. But on the upside, those larvae are, in essence, gathering food for the adults by consuming prey further down the food web.

sciencemag.org, 7 May 2020
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