Increasing jellyfish numbers are part of global cycle

Posted by Flora Malein

It’s good news for beach-goers as scientists believe that recent jellyfish blooms are just part of a natural cycle.

As the number of jellyfish in our oceans has risen over the past few years, many people believed that these numbers were set to increase in the future. Jellyfish blooms create big problems for fishermen, painful stings for swimmers and even cause issues on land such as choking up pipes that supply cooling water to power plants.
 
However, a new study suggests that rather than an increasing trend, recent high numbers of jellyfish are instead part of a natural global cycle that fluctuates over a 20 year period. The natural cycle hit a rise in the 1990s and early 2000s, which led to the current perception that jellyfish numbers have increased recently. Their findings suggest that overall jellyfish numbers have remained relatively constant over the past two centuries
 
"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," says marine scientist Rob Condon. 
 
The researchers looked at all long term data-sets that documented changes in jellyfish numbers from around the globe. They believe that it is a couple of recent case studies that has led other scientists and the media to report a recent rise in jellyfish numbers. While jellyfish numbers have increased in some locations, in others they have remained stable, fluctuated or even decreased.
 
The study did find a hint of an increase in jellyfish numbers outside the normal cycle in the 1970s but further investigation is required to confirm whether this is anything out of the ordinary.
 
"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, a marine scientist and co-author of the paper published in the Proceedings of the National Academy of Science.
 
"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," she adds.