Are Jellyfish Populations Increasing?

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.

High noon in Arctic winter

Dawn duty? Collecting a final sample before dinnertime? No, this is what the middle of the day looked like for scientists and crew who voyaged to the Chukchi Sea this past winter.

Carin Ashjian, a biologist at Woods Hole Oceanographic Institution, led the first research cruise ever conducted in the ice-covered Chukchi Sea waters during winter, when the sun appears for only a few hours a day and never rises higher than a few degrees above the horizon. Wind chills reached as low as -40°F.

Researchers from WHOI and the universities of Alaska and Rhode Island spent 40 days on the U.S. Coast Guard icebreaker Healy in the Bering and Chukchi Seas in the late fall of 2011 as ice and darkness closed in. They investigated water conditions and marine life at the base of the Arctic food chain. Their findings were surprising: Far from shutting down for the season, “the biological community was still very active,” Ashjian said.

Learn more online about the historic trip:

Cruise blog (http://arctic-winter-cruise.blogspot.com/)

Audio slideshow (http://www.whoi.edu/oceanus/feature/into-the-dark-and-ice)

Can whales get the bends

Scuba divers can get decompression sickness, or the bends, a painful and potentially fatal condition, from ascending too quickly from a deep dive. That causes dissolved gas to come out of solution and form bubbles in the body. But can whales and dolphins get the bends?

To find out, biologist Michael Moore and colleagues at Woods Hole Oceanographic Institution looked closely at marine mammals stranded ashore and reported evidence of decompression sickness in December 2011 in the journal Proceedings of The Royal Society B.

They found evidence, for example, in the rib of a dead sperm whale that washed ashore on Nantucket (above). A lesion in the bone was likely caused by nitrogen bubbles that formed when the whale rose too rapidly from high-pressure depths. The bubbles, though tiny, obstructed blood flow and led to bone damage.

“Until recently the dogma was that marine mammals have anatomical and physiological and behavioral adaptations to make the bends not a problem,” said Moore, who is director of the Marine Mammal Center at WHOI. “There is no evidence that marine mammals get the bends routinely, but a look at the most recent studies suggests that they are actively avoiding, rather than simply not having issues with, decompression.”

In other words, extraordinary occurrences, such as sonar, for example, could cause marine mammals to alter their usual diving behavior in ways that can give them the bends.

See “Deadly diving? Physiological and behavioural management of decompression stress in diving mammals” in Proceedings of the Royal Society B.