There’s a shift happening in the way scientists are thinking about how ocean acidification affects marine creatures. Originally, when researchers in the Southern Ocean watched the shells of tiny marine snails dissolve in high-carbon dioxide water, they suspected that similar animals with calcium carbonate shells and skeletons would most likely be harmed by ocean acidification. After all, this made intuitive sense: Ocean acidification means there is more carbon dioxide in the water, which lowers the water’s pH. All of this decreases the amount of carbonate ions in the ocean—the chemical building blocks found in animals’ shells. Wouldn’t decreases in these building blocks rob animals of the very things they need to build their shells?
Ocean acidification biological research has looked at this “building blocks” hypothesis for a while. Many excellent studies have shown that time after time, decreases in seawater carbonate ion levels are associated with decreases in shell building by corals, plankton, oysters, and more. But that clear relationship doesn’t hold for crabs and lobsters, even though they too have calcium carbonate in their shells. And different shell formers respond to different degrees of change. What’s going on?
The newest generation of research points to energy, or the lack of it, as the culprit. Presentations at yesterday’s ocean acidification sessions at the 2014 Ocean Sciences Meeting showed that algae, red coral, mussels, and even very young Dungeness crabs — all shell builders — are most likely not suffering from a lack of shell building blocks. Rather, the problem is bigger. They’re spending more energy existing in water chemistry that just isn’t very comfortable overall, so they have less energy for growing, reproducing, and surviving. Younger, fast-growing organisms tend to take it harder than older ones, since they don’t have a lot of reserves to draw from. This “energy crisis” hypothesis also helps explain some other ocean acidification response results of higher animals without shells, like squid and finfish.
To understand exactly what’s going on, we need new kinds of experiments to look at the different amounts of energy species need to survive and thrive. That’s the next horizon in ocean acidification research!
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