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Hold the jellyfish burger. Blooms of the gelatinous creatures may be caused by natural cycles rather than being a consequence of overfishing and climate change.
It had been widely thought that huge blooms of the creatures were likely to become increasingly common as the oceans warm and overfishing empties the seas of their natural predators.
Eating them seemed to be the only obvious solution, especially in a world where the human population and the need for new food supplies is rising. Already, jellyfish burgers, jellyfish ice cream and jellyfish biscuits have been developed.
But a new scientific study suggests that rather it is long-term natural population cycles that have driven the increase in jellyfish blooms rather than environmental problems.
While recognising the damage that blooms can do to tourism and industries such as fishing where nets get clogged up, the international team of researchers found “no robust” evidence to show that jellyfish are significantly on the rise.
“There is, overall, no significant increase in jellyfish abundance over the observational period (1874–2011),”
they concluded as they reported in the journal Proceedings of the National Academy of Sciences.
Blooms that have previously been cited as evidence of the impacts of climate change or overfishing include the appearance of millions of the warty comb jelly, Mnemiopsis leidyi, in the Black Sea, which they said had collapsed by the late 1990s. Another area was the Bering Sea where blooms have now slumped back to “low or moderate levels”.
Small increases that have been observed could be driven by human activities, they agreed, but said more research needs to be carried out to determine the extent.
By using data on jellyfish sightings dating back to 1874 the researchers found that there is a 20-year cycle in which populations rise and fall naturally. Other gelatinous creatures such as salps were included in the study.
And they observed that for many jellyfish species the most recent natural boom in numbers coincided with the period – the 1990s and early 2000s – when concerns about global warming and the health of the oceans was suddenly becoming major public issues.
The previous boom in numbers was in the 1970s and went unnoticed, it was suggested, because there was less awareness of worldwide problems and, with the internet yet to be devised, it was much harder to share and find information.
Dr Cathy Lucas, of the University of Southampton, was one of the researchers involved in the study and said: “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.
“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.
“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.”
Dr Rob Condon, of the Dauphin Island Sea Lab (DISL) in Alabama, US, said: “The realisation 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.”
