Sensitivities of animal taxa to ocean acidification. Fractions (%) of coral, echinoderm, mollusc, crustaacean, and fish species exhibiting negative (red), no (yellow), or positive (green) effects on performance indicators reflecting individual fitness in response to the respective pCO2 ranges. Graphic: Astrid C. Wittmann and Hans-O. Pörtner, 2013

By Brad Plumer
31 August 2013 (Washington Post) – The world’s oceans are turning acidic at what’s likely the fastest pace in 300 million years. Scientists tend to think this is a troubling development. But just how worried should we be, exactly? It’s a question marine experts have been racing to get a handle on in recent years. Here’s what they do know: As humans keep burning fossil fuels, the oceans are absorbing more and more carbon-dioxide. That staves off (some) global warming, but it also makes the seas more acidic — acidity levels have risen 30 percent since the Industrial Revolution. There’s reason for alarm here: Studies have found that acidifying seawater can chew away at coral reefs and kill oysters by making it harder to form protective shells. The process can also interfere with the food supply for key species like Alaska’s salmon. But it’s not fully clear what this all adds up to. What happens if the oceans keep acidifying and water temperatures keep rising as a result of global warming? Are those stresses going to wipe out coral reefs and fisheries around the globe, costing us trillions (as one paper suggested)? Or is there a chance that some ecosystems might remain surprisingly resilient? That’s one of the big outstanding questions on climate change. “We understand the physics of simple things like how oceans become acidic,” said Richard Norris, a paleobiologist at Scripps Institution of Oceanography, UC San Diego. “But when it comes to how ecosystems might react, that’s big and complex and messy, with all these interactions going on, both physiological and how organisms interact with each other.” […] So, recently, biologists at the Alfred Wegener Institute in Germany decided to try to combine the two approaches. They tallied up much of the field research that’s been done to date and compared it against the fossil record, in an attempt to get a broad overview of the effects of acidification on corals, molluscs, echinoderms, crustaceans, and fishes. The results, published this week in Nature Climate Change, aren’t exactly encouraging: “Our analysis demonstrates that all considered groups are impacted negatively, albeit differentially, even by moderate ocean acidification.” Here’s what that looks like in chart form — the red bars show that the number of “negative effects” on the fitness of species tend to go up as the amount of carbon in the ocean increases. [more]

The oceans are acidifying at the fastest rate in 300 million years. How worried should we be?