Mythical boom in jellyfish blooms

Where is the hard evidence?

February 2012: Claims that the number of jellyfish are increasing have been questioned in a new global study.

Blooms, or proliferation, of jellyfish have shown a substantial, visible impact on coastal populations - clogged nets for fishermen, stinging waters for tourists, even choked intake lines for power plants - and recent media reports have created a perception that the world's oceans are experiencing increases in jellyfish due to human activities such as global warming and overharvesting of fish.

HIGH IMPACT: Giant jellyfish clog fishing nets in Japan

Now, a new global and collaborative study questions claims that jellyfish are increasing worldwide and suggests claims are not supported with any hard evidence or scientific analyses to date.

Understanding what happens in the long-term is the key‘Clearly, there are areas where jellyfish have increased - the situation with the giant jellyfish in Japan is a classic example,' says Dr Cathy Lucas, a marine biologist at the University of Southampton, and a co-author of the study. ‘But there are also areas where jellyfish have decreased, or fluctuate over the decadal periods.'

Dr Lucas says understanding the long-term rather than short-term data is the key to solving the question about jellyfish blooms.

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 co-author Dr Carlos Duarte. ‘The important aspect about our synthesis is that we will be able to support the current paradigm with hard scientific data rather than speculation.'

Are humans affecting jellyfish populations?The study has led to the formation of a global database called the Jellyfish Database Initiative (JEDI) - a community-based database project that is being used in the global analysis.

The database consists of more than 500,000 data points about global jellyfish populations collected from as early as 1750, and will be made as a future repository for datasets so that the issue of jellyfish blooms can be continually monitored in the future.

By analysing JEDI, the group will be able to assess key aspects behind the paradigm including whether current jellyfish blooms are caused by human-made actions or whether we are simply more aware of them due to their impact on human activities, such as overharvesting of fish and increased tourism. The global analyses using JEDI are now underway, and the project is set to finish this spring.

http://www.wildlifeextra.com/go/news/jellyfish-population.html