Unless humans act now, seafood may disappear by 2048, concludes the lead author of a new study that paints a grim picture for ocean and human health.

According to the study, the loss of ocean biodiversity is accelerating, and 29 percent of the seafood species humans consume have already crashed. If the long-term trend continues, in 30 years there will be little or no seafood available for sustainable harvest.

The increasing pace of diversity loss thus imperils the "ecosystems services" that many human populations depend on for survival, the study says.

The research also found that biodiversity loss is tightly linked to declining water quality, harmful algal blooms, ocean dead zones, fish kills, and coastal flooding. (Related: 'Dead Zone' off Oregon Coast Is Growing, Study Says" [August 4, 2006].)

"Biodiversity is a finite resource, and we are going to end up with nothing left ... if nothing changes," said Boris Worm, an assistant professor of marine conservation biology at Dalhousie University in Halifax, Canada.

Worm led the international team of scientists and economists that examined the role of marine biodiversity in maintaining ecosystem services. The research appears in tomorrow's issue of the journal Science.

But areas managed for improved biodiversity can and do recover, Worm says, raising the possibility that the trend can be reversed if humans take action.

"Where we [protect marine areas] around the world—from the tropics to temperate ecosystems—we see an increase in species diversity and productivity and stability and economic revenue from those ecosystems," he said.

Consistent Response

Worm and colleagues examined the impact of species loss at local, regional, and global scales and in a variety of ecosystems.

Everywhere they looked, they got the same result: The greater the loss of diversity, the greater the impact on ecosystem services.

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"Ecosystems that were losing species were always more fragile, always more vulnerable, always more likely to see a whole collapse of fisheries, more likely to show an increase in toxic events like fish kills and things like that," Worm said.

"Whereas those systems that still had a full portfolio of species or had large species diversity to begin with were more robust, better buffered against change."

In a telephone briefing with reporters, Worm added that he and his colleagues were "really surprised, to some extent shocked, by the consistency of the result."

Worm told National Geographic News that the tight-knit connections between ocean communities and their habitats might explain why species diversity affects ecosystem services so closely.

He likened the relationship to a house of cards: Remove one species or habitat type in the system, and the whole thing comes tumbling down.

But Donald Boesch at the University of Maryland Center for Environmental Science in Cambridge is not convinced.

In a Science news article on the study, he said "it falls short of demonstrating that biodiversity losses are the primary drivers of why the services have declined."

For example, excessive fertilizer runoff into the Chesapeake Bay is most likely behind the decline in water quality there, not loss of biodiversity, he says.

Reversing the Trend

But the finding that areas do recover if managed is a major bright spot to the otherwise dark study, Worm says.

"This can be done. It's not beyond our reach at all," he said.

The study recommends an ecosystem management approach that sets aside some zones completely off-limits to any human activity while opening others to certain uses, such as recreation, research, and fishing.

"It's exactly what we do on land, and we've been doing it for a long time," Worm said.

Jane Lubchenco, a marine biologist at Oregon State University in Corvallis, praised the study for presenting compelling evidence that ecosystems can recover if appropriate action is taken.

"That said, their first conclusion about the downward spiral [of biodiversity] suggests that the rate of implementation of those recovery tools needs to be sped up quite significantly," she said. But "just making recommendations doesn't make things happen, unfortunately."

However, she points to several promising developments, including a proactive movement toward marine reserves and protected areas off the coast of California and Australia's Great Barrier Reef. (Related: "Giant Marine Reserve Created in South Pacific" [March 29, 2006].)

She also promotes "catch shares" fisheries management, in which commercial fishers have a stake in maintaining healthy fish populations because they are granted a percentage of the total allowable catch. As more fish are available, the fishers get a larger share.

"The whole idea is to align fishing and conservation interests so there is incentive for fishermen to conserve stocks so we have something to catch in the future," she said.

On the individual level, Worm says, people need to pay attention to what they eat.