WASHINGTON — Mass extinctions of species in the world's oceans are inevitable if current trends of overfishing, habitat loss, global warming and pollution continue, a panel of renowned marine scientists warned Tuesday.
The combination of problems suggests there's a brewing worldwide die-off of species that would rival past mass extinctions, the 27 scientists said in a preliminary report presented to the United Nations.
Vanishing species — from sea turtles to coral — would upend the ocean's ecosystem. Fish are the main source of protein for a fifth of the world's population and the seas cycle oxygen and help absorb carbon dioxide, the main greenhouse gas from human activities.
"Things seem to be going wrong on several different levels," said Carl Lundin, director of global marine programs at the International Union for Conservation of Nature, which helped produce the report with the International Programme on the State of the Ocean.
Some of the changes affecting the world's seas — which have been warned about individually in the past — are happening faster than the worst case scenarios that were predicted just a few years ago, the report said.
"It was a more dire report than any of us thought because we look at our own little issues," Lundin said. "When you put them all together, it's a pretty bleak situation."
Climate and coral
Coral deaths alone would be considered a mass extinction, according to study chief author Alex Rogers of the University of Oxford. A single bleaching event in 1998 killed one-sixth of the world's tropical coral reefs.
Lundin pointed to deaths of 1,000-year-old coral in the Indian Ocean and called it "really unprecedented."
"Not only are we already experiencing severe declines in many species to the point of commercial extinction in some cases, and an unparalleled rate of regional extinctions of habitat types (e.g. mangroves and seagrass meadows), but we now face losing marine species and entire marine ecosystems, such as coral reefs, within a single generation," the experts said.
The chief causes for extinctions at the moment are overfishing and habitat loss, but global warming is "increasingly adding to this," the report said.
Carbon dioxide from the burning of fossil fuels ends up sinking in the oceans, which then become more acidic, devastating sensitive coral reefs. Warmer ocean temperatures also are shifting species from their normal habitats, Rogers said. Non-native species moving into new areas can cause havoc to those ecosystems.
Jelle Bijma, of the Alfred Wegener Institute, said the seas faced a "deadly trio" of threats of higher temperatures, acidification and lack of oxygen that had featured in several past mass extinctions.
Runoff from fertilizers into rivers and seas has reduced oxygen in those areas, creating dozens of "dead zones" around the globe. The U.S. Geological Survey earlier this month said it expects the dead zone from the Mississippi River to set a record when it builds later this summer due to flooding runoff.
"From a geological point of view, mass extinctions happen overnight, but on human timescales we may not realize that we are in the middle of such an event," Bijma wrote.
Chemicals and plastics from daily life also are causing problems for sea creatures, the report said. Overall, the world's oceans just cannot bounce back from problems — such as oil spills — like they used to because of all the compounding factors, scientists said.
Confounding the most dire predictions, the Gulf of Mexico has bounced back from last year's major oil spill, but it is still dealing with the growing "dead zone" and above average sea temperatures.
Similar 'stressors' in past extinctions
Describing the multiple events affecting the world's oceans as high intensity "stressors," the experts said similar compounding led to the previous five mass extinction events in the past 600 million years — most recently when the dinosaurs vanished 65 million years ago, apparently after an asteroid struck.
The conclusions follow an international meeting this spring in England to discuss the fate of the world's oceans. A full report will be published later this year, the panel said.
Lundin said that "some of these things are reversible if we change our behavior."
Overfishing is the easiest for governments to address, the experts said.
"Unlike climate change, it can be directly, immediately and effectively tackled by policy change," said William Cheung of the University of East Anglia. "Overfishing is now estimated to account for over 60 percent of the known local and global extinction of marine fishes."
Among examples of overfishing are the Chinese bahaba. Its swim bladder is desired in Asia as a medicinal product, and the cost per kilo (2.2 pounds) has risen from a few dollars in the 1930s to $20,000-$70,000 today.
Listed as critically endangered, the bahaba is just one of more than 500 marine species threatened by overfishing, Cheung noted. "The only chance for many of these species to recover is to stop overfishing and protect them so that the populations can rebuild," he added.
"If action is not taken immediately, our generation will see many more species follow the footsteps of the Chinese bahaba," Cheung said.
Fisheries improvement ignored?
On fisheries, at least, the report had some critics.
"It ignores all of the recent fisheries research showing stability or even recovery in fish populations as overfishing is reversed in many areas," said Trevor Branch, a University of Washington fishery sciences assistant professor.
He said he could only find one expert on the panel working on fisheries, Daniel Pauly of Canada's University of British Columbia, "and his inclination to apocalyptic rhetoric is well known."
Steve Murawski, a University of South Florida professor and previously chief science advisor for the U.S. National Marine Fisheries Service, said that "it's difficult to judge the veracity of the results or the scientific support" for the findings because the full report hasn't been published.
But he noted that in the United States "a strong set of management requirements backed by the force of law have resulted in an end to domestic overfishing."
"This is of course a very hopeful sign because the USA is such an important fishing nation," he added. "Is the record commensurate globally? No it is not, and thus I would certainly support" the panel's advice to reduce global fishing "to levels commensurate with long-term sustainability of fisheries and the marine environment."
The Associated Press and Reuters contributed to this report.