Written by DIVE Magazine Wednesday, 02 January 2013 11:46
Fears that global warming and marine environmental degradation is leading to a dramatic growth in jellyfish populations appears to be unfounded.
A study by marine biologists at the University of Southampton, in the latest issue of Proceedings of the National Academy of Sciences, suggests that the reported trends in jellyfish population explosions are overstated.
The key finding of the study shows global jellyfish populations undergo regular fluctuations with 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 before the spread of the Internet.
Dr Cathy Lucas, who is based at the National Oceanography Centre, Southampton, says: '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.'
To date, media and scientific opinion for the current perception of a global increase in jellyfish was supported by a few local and regional case studies. Although there are areas where jellyfish have increased; the situation with the giant jellyfish in Japan and parts of the Mediterranean are classic examples, there are also 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,' says 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.'
'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, in addition to begin monitoring jellyfish in open ocean and Southern Hemisphere regions that are underrepresented in our analyses,' says lead author Dr Rob Condon, marine scientist at the Dauphin Island Sea Lab (DISL) in Alabama.