Evidence that jellyfish are taking over the oceans is currently lacking, according to a new study published in Bioscience. Complied by a number of marine experts, the study found that while jellyfish have been on the rise in some regions it is likely due to a natural cycle of jellyfish populations and not a global boom. Researchers, including a number of marine biologists, have warned for years that jellyfish numbers may be exploding due to human activities, such as overfishing, warmer oceans due to global climate change, and the rise of oxygen-depleted, so-called “dead zones.”
“Clearly, there are areas where jellyfish have increased—the situation with the Giant Jellyfish in Japan is a classic example,” says lead author Rob Condon, marine scientist at the Dauphin Island Sea Lab (DISL) in the U.S. “But there are also areas where jellyfish have decreased, or fluctuate over the decadal periods.”
Looking over data going back to 1790, researchers did not see any long-term upswing in jellyfish populations, but rather boom-and-bust cycles that have been occurring for centuries.
“The past period of rise was in the mid-90s to about 2005, and that’s when all the papers claiming there was a global rise came out,” Carlos Duarte, director of the Oceans Institute at the University of Western Australia, told the Australian Broadcasting Corporation (ABC). “So in fact there was a little bit of support for that because there was more a general rise than the previous decade, but this is not unprecedented. If we looked at these with a longer time perspective we see that similar events have happened in the past.”
Still data on jellyfish populations in the past is “fragmented” according to Condon, making it difficult to get a clear picture yet of how jellyfish are responding to human-caused changes in marine environments. To deal with the dearth in data, the study has also announced a new global database, dubbed the Jellyfish Database Initiative (JEDI), that will help researchers track and understand changes in jellyfish populations.
“This is the first time an undertaking of this size on the global scale has been attempted, but it is important to know whether jellyfish blooms are human-induced or arise from natural circumstances,” says Condon. “The more we know, the better we can manage oceanic ecosystems or respond accurately to future effects of climate change.”
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