In recent years, media reports of jellyfish blooms and some scientific publications have fueled the idea that jellyfish and other gelatinous floating creatures are becoming more common and may dominate the seas in coming decades. The growing impacts of humans on the oceans, including overfishing and climate change, have been suggested as possible causes of this apparently alarming trend.

A careful evaluation of the evidence by Robert H. Condon of Dauphin Island Sea Lab and his 16 coauthors, however, finds the idea that jellyfish, comb jellies, salps and similar organisms are surging globally to be lacking support. Rather, Condon and his colleagues suggest, the perception of an increase is the result of more scientific attention being paid to phenomena such as jellyfish blooms and media fascination with the topic.

Also important is the lack of good information on their occurrence in the past, which encourages misleading comparisons. Condon and his coauthors describe their findings in the February issue of BioScience.

Such fossil and documentary evidence as is available 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 blooms drew less attention in decades and centuries gone by.

Condon and his coauthors do not urge complacency, 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.