Are jellyfish really taking over the world’s oceans?

Not necessarily, according to a study in the February 2012 issue of BioScience.

According to some media reports and scientific publications, jellyfish are becoming more common and might dominate the Earth’s oceans in coming decades. Jellyfish blooms are clogging fishermen’s nets, stinging swimmers, and even choking intake lines for power plants The reason, some suggest, is the increasing human impact on the planet’s oceans, including overfishing and climate change.

Moon jellyfish beach are stranding in San Francisco in November 2010. Image Credit: Ocean Beach Bulletin

But are jellyfish really taking over the world’s oceans? Not necessarily, according to a study in the February 2012 issue of BioScience. The researchers suggest that claims of an increase in jellyfish blooms around the world are not supported with any hard evidence or scientific analyses, but instead might be the result of more scientific attention and media fascination with the topic.

The report also points to the lack of good information on jellyfish blooms in the past, which encourages misleading comparisons. According to the report, the available fossil and documentary evidence indicates that occasional spectacular blooms of jellyfish are a normal part of such organisms’ natural history, and may be linked to natural climate cycles, but drew less attention in decades and centuries gone by.

Giant jellyfish clog fishing nets in Japan. Photo credit: Shin-ichi Uye

The report’s authors do not urge complacency, however, and acknowledge a lack of consensus among researchers. They point out that changes in populations of jellyfish and similar sea organisms do have important consequences for local marine ecology and could be affected by human activity. For that reason, they are assembling a comprehensive new database that will enable trends in the numbers of such creatures to be assessed and the links to human activity studied. But for now, Condon and his coauthors believe the case for jellyfish-dominated seas in coming decades is not proven.

The study was led by Rob Condon, marine scientist at the Dauphin Island Sea Lab in Alabama. Condon’s co-authors are comprised of experts from the Global Jellyfish Group, a consortium of approximately 30 experts on gelatinous organisms, climatology, oceanography, and socioeconomics from around the globe.

Bottom line: A study in the February 2012 issue of BioScience suggests that claims of an increase in jellyfish blooms around the world are not supported with any hard evidence or scientific analyses, and instead might be the result of more scientific attention and media fascination with the topic.

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