Invasive jellyfish-like creatures have a sinister secret to help them expand their tentacled reach into new waters. The prolific comb jelly turns to its offspring not as a means to grow the next generation but for its next meal, helping the species to travel through nutrient-poor waters across the planet.
Translucent ctenophores, also known as “sea walnuts”, are native to the east coast of North and South America. After first being observed in the Black Sea nearly 40 years ago, the stringless Mnemiopsis leidyi has since invaded and spread to the Caspian Sea and other Eurasian coastal waters, wreaking havoc on local environments and contributing to the collapse of local fisheries by outcompeting commercial fish, according to the Smithsonian.
But the success behind these peculiar animals’ ability to expand has been a bit of a mystery. Blooms of offspring have been observed in waters around the world that appear to lack the nutrients needed to support survival. An international team of researchers collected comb jellies over the course of a year off of the coast of northern Germany and observed teeny, tiny little jellies inside the bodies of larger transparent adults. Turns out, the brainless pelagic beasts were really just prepping for a perpetual harvest.
“We combined a study of the population dynamics of this species with experimental feeding and geochemical tracers to show, for the first time, that adult jellies were actually consuming the blooms of their own offspring,” said lead study author Jamileh Javidpour of the University of Southern Denmark in a statement.
Some jelly blooms may serve as a nutrient reservoir to provide food for up to three weeks in nutrient-poor waters, which could make the difference in life-or-death transects across the Atlantic Ocean.
"In some ways, the whole jelly population is acting as a single organism, with the younger groups supporting the adults through times of nutrient stress,” said Thomas Larsen, a co-author of the study at the Max Planck Institute for the Science of Human History.
"Overall, it enables jellies to persist through extreme events and low food periods, colonizing further than climate systems and other conditions would usually allow.”
The authors add that the findings also contribute to a broader understanding of the evolution of cannibalism throughout the animal kingdom, where more than 1,500 species – including our own – have been recorded feasting on their own species.
"Because comb jellies trace their ancestry back to the beginning of most animal life as we know it during the Cambrian Period, 525 Million Years Ago, it remains possible that it is a basic, unifying feature across the animal kingdom,” said Javidpour.
Understanding how, where, and why comb jellies spur such blooms could further help governing bodies combat their jelly invasions, which often have dire consequences for local economies and species.