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Cannibalism helps comb jellies survive harsh conditions, invade new environs

Cannibalism is key to the survival of the warty comb jelly, according to new research. Photo by Bruno Vellutini/Wikimedia
Cannibalism is key to the survival of the warty comb jelly, according to new research. Photo by Bruno Vellutini/Wikimedia

May 8 (UPI) -- The warty comb jelly, or sea walnut, is native to the coastal waters of the western Atlantic, but in recent decades, the gelatinous invertebrate has invaded the waters of Eurasia.

New research -- published this week in the journal Communications Biology -- suggests cannibalism is key to the species' ability to move into new environs.

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"We had this species arrive in the Black Sea in the 80s, and it arrived in the Caspian Sea in the 90s," Jamileh Javidpour, lead author of the new study and a professor of marine biology at the University of Southern Denmark, told UPI. "So it showed the ability to spread very fast over a diversity of ecosystems."

Most recently, the warty comb jelly, Mnemiopsis leidyi, has made its way to the Baltic Sea.

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Previous studies have identified a correlation between the arrival of the invasive cone jelly and declines in local fish stocks. When sea walnut blooms began appearing in the Baltic, researchers worried the local cod population would be negatively impacted.

In 2009, Javidpour published research reporting the discovery of warty comb jelly larvae in the guts of adult specimens, suggesting the jellyfish species occasionally practices cannibalism.

So when Javidpour and her research partners set out to understand how the invasive comb jelly can survive the long, cold winters in Baltic, they suspected its ability to eat its young might insulate the species from harsh conditions.

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"We studied these suspicions from the beginning, when they first arrived in our nets," Javidpour said.

Over a period of several months, Javidpour and her colleagues conducted rapid sampling efforts to see what the warty comb jellies in the Baltic were eating. They also analyzed changes in the comb jelly's population dynamics.

The population data showed the species produces more offspring during the late summer, while the sampling results revealed that as the warm season wanes and winter approaches, warty comb jelly larvae begin showing up in the guts of adults.

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"At the beginning we had plankton and other typical comb jelly prey," said Javidpour. "At the end of the season, we found that the larvae were permanently in the guts."

The findings suggest the warty comb jelly intentionally produces more offspring in anticipation of harsher conditions. When normal prey numbers decline during the winter, their own larvae become an essential source of nutrients.

"From our field data, we see a very clear shift to predating on their own kind when their traditional prey disappear," study co-author Thomas Larsen, researcher at the Max Planck Institute for the Science of Human History in Germany, told UPI.

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"In the beginning, we thought that this trait, producing more offspring right before winter, was a liability," Larsen said. "It now seems that it is giving them a competitive advantage."

According to Javidpour and Larsen, understanding the strategies different species use to successfully invade new territory and survive harsh conditions can help conservationists identify other invasive species that pose a heightened risk to native ecosystems. But the findings also have broad ecological implications.

"This research can help us to understand how animals adapt to sudden environmental changes and survive extreme conditions," Larsen said. "With the climate change It's not only about understanding invasion ecology, but also understanding systemic change."

Javidpour said she hopes to conduct followup studies of comb jellies in other regions to determine whether greater biodiversity -- the presence of wider variety alternative food sources -- influences the prevalence of cannibalistic behavior.

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