Some shelled animals will actually build stronger armour as climate change makes the sea more acidic, according to a paper published this month.

Increasing levels of carbon dioxide will mean an increase in the ocean’s acidity, which could make it harder for animals that use calcium carbonate to build their shells. But Justin Ries, of the University of North Carolina at Chapel Hill, found that some animals actually build more shell when levels of carbon dioxide are higher.

“Shelled marine organisms need carbonate ions to build their shells that protect them from the intense predation that defines everyday life on the shallow sea floor,” says Ries (UNC press release).

“The organisms that responded positively to higher carbon dioxide levels are apparently more adept at converting the elevated dissolved inorganic carbon in the seawater, which results from elevated atmospheric carbon dioxide, back into a form that they can use directly in their calcification. The others, however, appear to be less adept at manipulating dissolved inorganic carbon.”

Ries and colleagues from Woods Hole Oceanographic Institution grew 18 different species in tanks with differing levels of carbon dioxide. They found seven species had more shell under higher carbon dioxide: crabs, lobsters, shrimp, red and green calcifying algae, limpets and temperate urchins (image top – larger animal grew under higher carbon dioxide).

Another 10 species did worse: oysters, scallops, temperate corals, tube worms, hard and soft clams, conchs, periwinkles, whelks and tropical urchins (image lower – smaller animal grew under higher carbon dioxide). Only one species was unaffected, the humble mussel, they report in Geology.

“We were surprised that some organisms didn’t behave in the way we expected under elevated carbon dioxide,” says study author Anne Cohen of WHOI (WHOI press release). “We can’t assume that elevated carbon dioxide causes a proportionate decline in calcification of all calcifying organisms.”

One crucial piece of information is missing however – do the animals experiencing climate-related gigantism still taste good?

If you want to learn more about ocean acidification, Sigourney Weaver is on hand to help. The Alien actress has narrated a film on the subject entitled Acid Test for the Natural Resources Defense Council.

Image top: Justin Ries, UNC-Chapel Hill

Image lower: Tom Kleindinst, Woods Hole Oceanographic Institution