Experts Say Reports Of Increasing Jellyfish Populations Unjustified
January 1, 2013

Experts Say Reports Of Increasing Jellyfish Populations Unjustified

April Flowers for - Your Universe Online

A widely held perception of a global increase in jellyfish has been challenged by a new international study led by the University of Southampton.

Jellyfish proliferations, or blooms, have a visible and substantial impact on coastal populations, including clogged nets for fishermen, stinging waters for tourists, and even choked cooling intake pipes for power plants. A perception that the world's oceans are experiencing trending increases in jellyfish has been created by recent media reports.

However, the new study, published in a recent issue of Proceedings of the National Academy of Sciences (PNAS), suggests that these trends may be overstated. The team finds that there is no robust evidence for a global increase in jellyfish over the past two hundred years.

The study's key finding reveals that global jellyfish populations undergo concurrent fluctuations with successive decadal periods of rise and fall. This includes a rising phase in the 1990s and early 2000s, which contributed to the current perception of global increase of jellyfish abundance. During the 1970s, the period of high jellyfish numbers went unnoticed due to limited research on jellyfish at the time, less awareness of problems on a global scale, and limited information sharing capabilities such as the internet.

The authors detected a slight increase in jellyfish abundance since 1970, although there has been no increase over the long-term. The decreasing jellyfish populations over time countered the slight increase.

"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 from the National Oceanography Centre of Southampton.

A few local and regional case studies have been the basis for both media and scientific opinion for the current perception of a global increase in jellyfish. The authors admit there are areas where jellyfish have increased — for example, the situation with the Giant Jellyfish in Japan and parts of the Mediterranean — however, there are also areas where jellyfish numbers have remained stable, fluctuated over decadal periods, or actually decreased over time.

The study was motivated by increased speculation and discrepancies about current and future jellyfish blooms by the media and in climate and science reports.

"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," Dr Lucas said in a statement. "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 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," says Dr Rob Condon, marine scientist at the Dauphin Island Sea Lab (DISL).

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