Jellyfish, despite their delicate, squishy frames, have actually fared quite well in the face of climate change. While nearly every ocean-dwelling animal, from coral polyps to blue whales, is struggling to adapt to warmer waters, many jellyfish are indeed thriving, sometimes growing into vast, stinging masses that can cover as much as 30,000 square miles. These drifting mobs of jellies, known as jellyfish blooms, are generally thought to be harmful to both humans and other sea creatures, even prompting Korean scientists to create autonomous swarms of jellyfish shredding robots. But a new study shows that the jellies may not be all bad.
Previous research has found that juvenile fish sometimes gather among the tentacles of larger jellyfish, feeding on the plankton trapped among the tendrils, or perhaps using the jellyfish and their stinging tentacles as a shield from predators. A team of researchers from the United States and Japan thought that these congregations of jellyfish and their fish groupies might instead serve as a convenient hunting ground for diving seabirds. If that were true, it would be a rare benefit of jellyfish blooms, which are typically regarded as detrimental to top predators in ocean ecosystems. To find out, they strapped video loggers to eight thick-billed murre on St. George Island off the coast of Alaska in the eastern Bering Sea, and tracked the birds as they dove into patches of water filled with northern sea nettle, more commonly known as the brown jellyfish. Only four birds dove beneath the surface of the water while the cameras were recording, and they encountered jellyfish on 85 percent of the recorded dives, the researchers report today in Biology Letters. The birds approached jellies and plucked fish from among their tentacles in nearly 20 percent of the feeding events recorded—a relatively high number for a previously unobserved behavior.
While the sample size was small, the fact that all four birds fed on fish in jellyfish patches suggests that the behavior may be a common adaptation for diving seabirds. According to the authors, the findings support the hypothesis that jellyfish blooms might actually increase feeding opportunities for seabirds by concentrating prey in easily exploitable hunting grounds, or what the authors call "the jellyfish buffet."