Food-chain alarm from a low-ozone zone

It also damages the DNA of marine bacteria and the larvae of starfish and urchins, they say. And it even alters ocean chemistry, creating potentially dangerous substances in the water itself.

"It's really dramatic what the changes in ozone levels will do to rates of DNA damage and inhibited development," says biologist Deneb Karentz from her office at the University of San Francisco.

"If you have a 30 percent decline in ozone, that doesn't mean a 30 percent decline in a given biological process - it could be a lot more than that," she says.

The tricky part is estimating how damage to one group of organisms might affect others above or below it in the food chain. Ocean ecosystems are extremely complicated and poorly understood.

Phytoplankton concentrations may not be the main factor influencing, say, krill abundance, which also depends on ocean currents, predator-prey relationships, and the timing and extent of annual sea ice.

"It's a tough game to call," says Langdon Quetin of the University of California at Santa Barbara. Krill live in areas usually affected only every few days by the wobbling ozone hole. "So if you average the amount of time phytoplankton are exposed in those areas, their decline may be insignificant for the krill."

"On the other hand, increased UV may affect female krill directly through damage to their ovaries," he says. "It's too early to tell."

Scientists studying UV effects on different portions of the food chain now collaborate closely. Here aboard the National Science Foundation's ice-going research ship Laurence M. Gould, four separate teams coordinate experiments and sampling to begin teasing out relationships between effects on ocean chemistry, bacteria, phytoplankton, fish larvae, and krill.

Wade Jeffrey of the University of West Florida in Pensacola knows that bacterial growth is inhibited in water exposed to increased UV.

But it's not clear how much is caused by direct UV damage to the bacteria's DNA, as opposed to indirect damage from the way UV changes the chemistry of sea water.

So his team works closely on ship with chemical oceanographers Kenneth Mopper of Washington State University and David Kieber from the State University of New York College of Environmental Science and Forestry, in Syracuse.

Surface waters are laden with dissolved organic matter, from which UV can produce hydrogen peroxide and other substances hazardous to living tissues. But Dr. Kieber and Dr. Mopper have found that these substances can also help bacteria indirectly by breaking organic matter into forms the bacteria can consume.

'Good UV, bad UV'

Dr. Jeffrey calls this the "good UV, bad UV syndrome." UV may harm bacteria during short-term exposures, but that could be compensated for by increased food sources over the long haul. Or the organisms may adapt to the new conditions over time.

Determining the net result will require more analysis, further experiments, more hours on deck in the frigid Southern Ocean.

"The Southern Ocean runs around the world, connects all the other oceans, and drives many of their currents and nutrient supplies," Jeffrey says.

"The broader concern is that a significant change in the Southern Ocean can impact production in other oceans."

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