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bara. The group analyzed surveys of species’abundance from 16 sites around the Chan-nel Islands National Park. They also exam-ined satellite data from 1999 to 2002 onchlorophyll concentrations—an indirectindication of nutrient levels—in the oceanwaters surrounding the islands.

The “top-down” control accounts for 11 to 20 percent of the ecosystem’s patternof species abundance, the team reports inthe May 26 Science. The predator popula-tions have 7 to 10 times as much influenceover the ecosystem as the availability ofnutrients does.

“No one has tested these two factors atthe same time,” says Halpern. “How healthya kelp-forest community is depends prima-rily on which predators and how many ofthem you have in the community.” Over-fishing that depletes these predator popu-lations could affect the ecosystem’s stability.

“I think this is a very powerful paper interms of suggesting the strength of top-down influences,” says Robert S. Steneck ofthe University of Maine in Orono. “As webasically fish down global food webs in allthese different ecosystems, we will inessence be restructuring communities.”

James Estes of the University of Califor-nia, Santa Cruz agrees that the work isimportant to fisheries management. “It pro-vides further evidence for the notion thatoverfishing has a strong effect on the ecosys-tem. It’s not just the [fish] stocks beingtaken out.”

But Michael H. Graham of Moss Land-ing (Calif.) Marine Laboratories notes thatthe new study may have underestimatedthe bottom–up effect. He points out thatthe 1999–2002 satellite data cover a periodwithout an El Niño or La Niña event, twoweather phenomena that can have largeimpacts on nutrient prevalence in kelpforests. Furthermore, the satellite measureschlorophyll concentrations near, but not in,the kelp forests. —A. CUNNINGHAM

Open Water,Open MouthsScuba divers faceinfection risks

Circling sharks and empty air tanks mayhaunt scuba divers’ imaginations, but ordi-nary microbes are a far more probable haz-ard. A new study takes a stab at quantify-

ing the risks that waterborne bacteria andviruses pose to divers.

While scientists regularly measure bac-terial concentrations in waters used bybeachgoers, they don’t test all the sites vis-ited by divers, surfers, and kayakers. What’smore, researchers don’t know how much ofthe water these people swallow, says micro-biologist and mathematical modeler JackSchijven of the National Institute of PublicHealth and the Environment in Bilthoven,the Netherlands.

To begin measuring the microbial risk todivers, Schijven and his institute colleagueAna Maria de Roda Husman provided aquestionnaire to 233 professional diversand posted a similar survey online for about26,000 recreational divers in the Nether-lands. Thirty-seven pros—who do under-water-construction or search-and-rescuework, for example—and 483 amateursresponded. They supplied data on illnessesthey’d had in the past year, how many divesthey’d made in various aquatic environ-ments, and what volume of water they’dswallowed on a typical dive.

The researchers focused on skin, ear, eye,respiratory, or gastrointestinal symptoms,which might have been caused by infectionsacquired during dives. Most respondentssaid that they’d had at least one such illness.Diarrhea and ear problems topped the list.

“Only 20 percent of the divers stated thatthey did not have any complaint at all,”Schijven says. “We were really astonished.”

The study didn’t include a comparisongroup of nondivers, so it’s unclear what por-tion of the ailments resulted from diving, hecautions.

Other data from the questionnaires sug-gest that recreational divers face a gas-trointestinal infection risk of up to 1.1 per-cent per marine dive and 1.5 percent perfreshwater dive.

The recreational divers tended either toswallow no water or to swallow about the

volume of a shot glass. Professional divers,who often wear full face masks, generallyswallowed a few drops of water or less. Fromthe survey information and data on pathogenabundance, the researchers estimate in theMay Environmental Health Perspectives thatprofessionals face the highest risks.

The pros “have to dive in any kind ofwater, even wastewater,” Schijven says.

Overall, divers reported more ear com-plaints during the summer months thanthe winter months. That’s “a strong hint”that diving is to blame, Schijven says,because the bacterial suspects in such infec-tions prefer warm water. By contrast, gas-trointestinal problems, which are causedby pathogens that survive longer in coldwater, are most frequent during winter.

The study takes a “great approach” toexamining overlooked aspects of divers’health, says Richard E. Moon, a Duke Uni-versity physician and senior medical con-sultant for the Durham, N.C.–based DiversAlert Network. “It should raise divers’ levelof awareness of this potential risk,” he adds.However, he says, the results could bebiased because people with health com-plaints may have responded more readily tothe survey. —B. HARDER

For the BirdsNew vaccines protectchickens from avian flu

By piggybacking components of strains ofavian-influenza virus onto an existing poul-try vaccine, scientists have created experi-mental vaccines that can prevent bird flu inchickens, two studies show.

While researchers will need to further testthe novel vaccines in large numbers of fowland against various subtypes of bird flu, theearly results suggest that widespread vacci-

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SCIENCENEWSThis Week

A LOT TO SWALLOW Swallowing contaminated waters can cause infections in divers.

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