Study eyes global jellyfish populations

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Are jellyfish numbers increasing globally? One recent study suggests decadal fluctuations. Photo courtesy NOAA.

More long-term and widespread monitoring needed to pinpoint trends

By Summit Voice

FRISCO —Global jellyfish populations appear to fluctuate on a decadal basis, including an increase in the 1990s and early 2000s that has led to the current perception of an overall global increase in jellyfish abundance.

But reports that jellyfish are steadily increasing may be unfounded, according to a recent study led by researchers from the Dauphin Island Sea Lab in Alabama and the National Oceanography Centre, Southampton, UK, who concluded there is no robust evidence for a global increase in jellyfish over the past two centuries.

The researchers did find a hint of a slight increase in jellyfish since 1970, although this trend was countered by the observation that there was no difference in the proportion of increasing vs. decreasing jellyfish populations over time.

Some studies have suggested that increased jellyfish abundance could be due to global warming or coastal pollution, but the scientists said more long-term monitoring across a wider geographic area is needed to detect significant trends.

“The realization that jellyfish synchronously rise and fall around the world should now lead researchers to search for the long-term natural and climate drivers of jellyfish populations, in addition to begin monitoring jellyfish in open ocean and Southern Hemisphere regions that are underrepresented in our analyses,” said lead author Dr Rob Condon, a marine scientist at the Dauphin Island Sea Lab in Alabama.

Blooms of jellyfish can have a significant impact, including clogged fishing nets, stinging waters for tourists, even choked cooling intake pipes for power plants. Heightened web-based reporting may have fueled the idea that jellyfish populations are steadily proliferating, the researchers said.

The key finding of the study shows global jellyfish populations undergo concurrent fluctuations with successive decadal periods of rise and fall, including a rising phase in the 1990s and early 2000s that has contributed to the current perception of a global increase in jellyfish abundance.

The previous period of high jellyfish numbers during the 1970s went unnoticed due to limited research on jellyfish at the time, less awareness of global-scale problems and a lower capacity for information sharing.

“Sustained monitoring is now required over the next decade to shed light with statistical confidence whether the weak increasing linear trend in jellyfish populations after 1970 is an actual shift in the baseline or part of a larger oscillation,” said Dr. Cathy Lucas, who is based at the National Oceanography Centre.

The evidence for increasing jellyfish numbers is based on a handful of local and regional case studies, including a well-documented surge in the giant jellyfish population on the coast of Japan. But there are other areas where jellyfish numbers have remained stable, fluctuated over decadal periods, or actually decreased over time.

Increased speculation and discrepancies about current and future jellyfish blooms by the media and in climate and science reports formed the motivation for the study.

“There are major consequences for getting the answer correct for tourism, fisheries and management decisions as they relate to climate change and changing ocean environments,” said Dr. Lucas. “The important aspect about our work is that we have provided the long-term baseline backed with all data available to science, which will enable scientists to build on and eventually repeat these analyses in a decade or two from now to determine whether there has been a real increase in jellyfish.”

Given the potential damage posed by jellyfish blooms to fisheries, tourism and other human industries, the findings of the group foretell recurrent phases of rise and fall in jellyfish populations that society should be prepared to face.

The results of the study, which includes lead co-author Dr Cathy Lucas, a marine biologist at the University of Southampton, appear in the latest issue of Proceedings of the National Academy of Science (PNAS manuscript # 2012-10920R).

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