Not all species equally affected by more acidic oceans

When atmospheric carbon dioxide dissolves into the ocean, it forms carbonic acid, which in turn lowers the water’s pH levels and causes oceanic acidification. The phenomenon is expected to occur at increasing rates as carbon dioxide emissions around the world continue to rise.

In a report published in Nature Climate Change, two researchers from the Alfred Wegener Institute, Helmholtz-Centre for Polar and Marine Research (AWI) in Bremerhaven, Germany performed an extensive research review that indicated the impacts of a more acidic ocean will vary from one species to the next.

The review included data on over 150 different species from five animal taxa: corals, crustaceans, mollusks, vertebrates and echinoderms. The German scientists also used the same emission scenarios for carbon dioxide as those that were used to draft the world climate report, allowing them to make projections into the distant future.

“Our study showed that all animal groups we considered are affected negatively by higher carbon dioxide concentrations. Corals, echinoderms and mollusks above all react very sensitively to a decline in the pH value,” said study co-author Astrid Wittmann, a marine biologist from AWI.

While echinoderms such as brittle stars were expected to be significantly challenged by the elevated carbon dioxide values predicted for the end of this century, only higher concentrations of the greenhouse gas were thought to impact crustaceans like the Atlantic spider crab. If global temperatures rise as currently predicted, the impacts of a more acidic ocean could be more severe, the researchers said.

The study also examined some of the specific physiological impacts of a lower pH in the world’s oceans.

“For example, we considered whether metabolism, growth, calcification or behaviour change in high carbon dioxide concentrations,” said co-author Hans-Otto Pörtner, an AWI professor who primarily researches the biological impacts of changing climates.

The research team said the nature and habits of different animal species are major factors in how ocean acidification impacts their bodily functions. For example, fish and other vertebrates are better able to cope with falling pH levels because they are physically active and mobile, while relatively immobile corals will find it more difficult to adapt due to a lack of physiological options.

Evidence in the fossil records also supports the notion that fish are better equipped to handle changes in the ecosystem’s pH. The researchers said they found that the spread of the corals and the size of the reefs fell drastically around 55 million years ago during a similar climate crisis, while fish were able to extend their dominance.

“We compared our results with the widespread deaths of species around 250 and 55 million years ago when CO2 concentrations were also elevated,” Pörtner said. “Despite the relatively rough statements we were able to make with the assistance of sediment samples from the past, we discovered similar sensitivities in the same animal taxa.”

The climatologist added that they were surprised to learn fish in the ancient past were not highly sensitive to acidic water because current research has indicated that larval-stage fish are quite sensitive to ocean acidification.

“Not all effects we are currently measuring are decisive for the destiny of a species possibly in the long term,” Pörtner suggested.

Brett Smith,, 26 August 2013. Article.

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