Skip to: Content
Skip to: Site Navigation
Skip to: Search

Are we causing a mass extinction in our oceans?

Research shows that many areas of today's oceans have conditions that parallel those of 250 million years ago, when 95 percent of marine species quickly died out.

(Page 3 of 4)

Not least among the victims of acidification are corals, whose growth is inhibited in affected waters. But climate change poses another problem for coral reefs: Sunlight and small increases in water temperature cause corals to expel the symbiotic algae that provide them with energy, which causes them to turn white, an effect called bleaching that can be short-lived or fatal. Mass bleaching was first observed in the late 1970s. By 2008, an estimated 19 percent of the world's coral reefs had been lost and 35 percent seriously threatened.

Skip to next paragraph

Coral bleaching has an impact on not just the corals. Reefs are key habitats for many marine species.

"Perhaps 25 percent of ocean species spend at least part of their life cycle on coral reefs," said Ken Caldeira with the Carnegie Institution for Science. "When we lose corals, we are likely to lose many of these species."

A recently published paper in the journal Nature documented what may be another domino in the decline of the oceans, this one at the very base of the marine food chain. Over the past century, the authors found, global phytoplankton levels have declined by 1 percent per year, a phenomenon they link to warming ocean surfaces.

Incidental victims

Amid the specter of climate change, the most immediate threat to species and ecosystems is overfishing, according to Susan Lieberman, director of international policy with the Pew Environmental Group.

"We should not take out more than is being produced," Lieberman said. "It sounds very logical, but that is not what is happening."

Sharks are emblematic of this problem. The International Union for Conservation of Nature has listed about a third of all open-ocean shark species as threatened with extinction due to overfishing.

In addition to removing seafood, some fishing practices kill other creatures incidentally, a phenomenon known as bycatch. Sea turtles are among the victims of this problem; a study published in April estimated that millions of sea turtles have been inadvertently caught as part of commercial fishing over the past 20 years.

Bottom trawling — in which a large, heavy net is dragged over the sea floor — is another problem, as it destroys habitat, according to the Pew Environmental report "Protecting Life in the Sea." This report cites studies suggesting 90 percent of the world's large fish have disappeared and that nearly one third of the world supply of commercially caught fish has collapsed.

Not everyone believes that fisheries are in immediate peril though.