A multinational group of researchers has challenged the widely held belief that there has been a global increase in jellyfish. According to the researchers, jellyfish blooms can have a significant impact on coastal populations, clogging nets for fishermen, stinging swimmers and sometimes blocking cooling intake pipes for power plants. The media has helped to create the perception that the Earth’s oceans are undergoing trending increases in jellyfish. This latest study suggests, however, that these trends are probably overstated, revealing that there is no strong evidence for a global increase in jellyfish over the past two-hundred years.
The key discoveries of the study reveal that global jellyfish populations are subjected to concurrent fluctuations with successive decadal periods of rise and fall. Researchers note, however, that a rising phase in the 1990s and early 2000s likely contributed to the current perception of a global increase in jellyfish numbers. They contend that a previous rising phase during the 1970s went unrecorded due to limited research on jellyfish at the time and a dearth of ways to share information.
Researchers have measured a slight increase in jellyfish abundance since 1970, but they contend that this trend was countered by the conclusion that that there was no difference in the proportion of increasing versus decreasing jellyfish populations over time.
“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,” says Cathy Lucas, from the National Oceanography Centre.
Most of the media hype about jellyfish blooms has been centered around several local and regional case studies, note researchers. There are areas where jellyfish numbers have increased, researchers admit, but there are also areas where jellyfish numbers have remained stable or even decreased over time.
Researchers decided to conduct this study because of the media hype over jellyfish blooms and the potential consequences of this hype.
“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 Ms. 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.”
Researchers hope that this study will convince scientists to search for the long-term drivers of jellyfish numbers.
“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 lead author Rob Condon, marine scientist at the Dauphin Island Sea Lab.
This study should help humans determine how jellyfish populations will impact various human industries in the near and distant future. According to the National Science Foundation, when jellyfish populations increase in a specific area, they increase quickly because jellyfish grow fast and reproduce at a rapid rate.
You can view a list of recent jellyfish bloom sightings at jellywatch.org.
The study’s findings were recently published in the latest issue of the journal Proceedings of the National Academy of Science.