Troubled waters

A new report has made dire predictions about ocean ecosystems. Has it gone too far?
July 20, 2011
Ocean scene: the light blue-green spots are caused by microscopic marine plants known as phytoplankton—some of which are toxic




The global oceans are in a very bad way, according to scientists at an April meeting of the International Programme on the State of the Ocean (IPSO). When a summary report from the meeting was released in June, it spawned disaster-movie headlines. The future of the ocean’s ecosystem looks “far worse than we had realised,” said Alex Rogers, director of IPSO and a professor in conservation biology at Oxford. “If the ocean goes down, it’s game over.”

Are things really so bad? According to Hugh Ducklow, director of the Ecosystems Centre at Woods Hole, Massachusetts (one of the US’s most prestigious marine biology laboratories), IPSO isn’t exaggerating. “If anything,” says Ducklow, who is not a part of IPSO, “the true state of the ocean is probably worse than the report indicates.”

The IPSO meeting addressed threats to ocean ecosystems including over-exploitation of fish stocks, acidification (caused by rising levels of atmospheric carbon dioxide), vanishing coral reefs and—unglamorously but crucially—changes to plankton growth, on which the entire food chain depends.

Phytoplankton are microscopic plants that bloom in the upper ocean and dictate the cycling of carbon between the ocean and atmosphere. Some phytoplankton are toxic, and when growth is artificially stimulated by nutrients in fertilisers and sewage (eutrophication), they poison their environment. Worse, bacteria feeding on decaying phytoplankton consume oxygen in the water, turning it into a dead zone. Oxygen depletion (hypoxia or, if total, anoxia) is also caused in deep water over much longer timescales by warming of the upper ocean, which suppresses the circulation of oxygen-rich surface water to the depths.

Also discussed at the meeting was the faster-than-expected melting of Arctic sea ice: summer at the North Pole could be ice-free within 40 years. The melting of ice from Antarctica and Greenland is also exceeding the predictions of many climate models. Coupled with expansion of water caused by warming, this may lead to a sea level rise of 0.5-1.2 metres by the year 2100.

The geological record shows at least five mass extinctions, in which most species on the planet vanished. “We now face losing marine species and entire marine ecosystems, such as coral reefs, in a single generation,” reads the IPSO report. “Unless action is taken now, the consequences of our activities are at high risk of causing the next globally significant extinction event.”

Ducklow admits such conclusions are based on inadequate observations—over too small an area, and for too short a time. But he feels that, as both concern and surveillance increases, “we will discover things are worse, not better, than we think.”

Andrew Watson at the University of East Anglia, an expert on the interactions of oceans and climate, also agrees with IPSO’s conclusions. “We suspect that at past crises, the real killer was widespread ocean anoxia. This is something that eventually the changes brought about by humans, particularly increased eutrophication and global warming, could bring on.” But he has qualms about the way these claims were presented. “Such a change to the life-support systems of the Earth is still a long way in the future… thousands or tens of thousands of years.”

Watson agrees on the urgent need for action, but adds: “We create a false impression if we say that we have to act tomorrow to save the Earth… I don’t find that kind of environmental catastrophism very helpful because it simply fuels a bad-tempered ideological and political argument instead of a well-informed scientific one.”

Ducklow insists that a plan is needed, which should include serious and immediate regulation of fishing, pollution and carbon emissions and “a comprehensive, global ocean observation system.” “What’s really needed is a long-term plan to reduce our impact on the oceans,” agrees Watson.

The full report by IPSO is published later this year; hopefully its tone will not distract from its findings.