Are jellyfish numbers on the increase? Southampton scientists study the evidence

Studying the evidence, researchers believe global jellyfish populations rise and fall over periods of approximately ten years and there is little to suggest major increases over the past two centuries. While, numbers of Giant Jellyfish have gone up in certain areas such as Japan and parts of the Mediterranean, populations have fallen in other areas.

Blooms, or proliferations, of jellyfish can show a substantial, visible impact on coastal populations - clogged nets for fishermen, stinging waters for tourists, even choked cooling intake pipes for power plants.

Recent media reports have created a perception that the world's oceans are experiencing trending increases in jellyfish. This 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, who is based at the National Oceanography Centre, Southampton.  "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 results of the study appear in the latest issue of Proceedings of the National Academy of Science (PNAS manuscript # 2012-10920R).