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Are Jellyfish Populations Increasing?

... and other WHOI research news

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Delicate but armed, mindless yet unstoppable, jellyfish sometimes appear abruptly near coasts in staggering numbers that cause problems and generate headlines: Jellyfish fill fishing nets in Japan, sinking a boat. Jellyfish clog nuclear plant water intakes. Gelatinous animals decimate fish stocks. Dangerous jellyfish inhabit areas where they haven’t been seen before. Is this a glimpse of the future ocean?

Scientists and others have speculated that the frequency of such blooms is rising, possibly related to warming oceans, nutrient pollution, or overfishing. Seventeen specialists on gelatinous animals convened to explore whether blooms are actually increasing—or whether increased observing efforts, public attention, and global media help create the perception of a jellyfish upsurge. The group included Larry Madin, a biologist and director of research at Woods Hole Oceanographic Institution, and former WHOI/MIT Joint Program student Kelly Sutherland.

The scientists examined documented jellyfish aggregations, from fossil records and ancient historical records through modern scientific and news reports. Reporting in the February 2012 issue of BioScience, the group concluded that there is not enough evidence to support the view that jellyfish blooms are on the rise.

"Despite a popular idea that jellyfish are taking over the oceans, this study shows that bloom populations have occurred throughout history," Madin said, "and we don't have enough data now to conclude we are seeing a new global phenomenon. Population fluctuations will continue—sometimes traceable to human impacts such as overfishing and sometimes with consequences for human activities.”

The group has established a global database for past, current, and future reports of gelatinous zooplankton, to provide an organized way to track and compare jellyfish occurrences.

Funding for the study was provided by the National Science Foundation, the University of California at Santa Barbara, and the State of California.


Dense coastal aggregations or "blooms" of gelatinous animals, such as this purple Pelagia jellyfish, can cause problems for people, including clogging fishing nets and consuming larvae of commercially important fish. People have suggested that these blooms are happening more frequently globally. To find out, gelatinous animal specialists from around the world examined and analyzed documented blooms ranging from fossil records through modern reports. (Photo by Larry Madin, Woods Hole Oceanographic Institution)

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