While research has shown that ocean acidification threatens many invertebrate marine species, such as clams and corals, by hindering their ability to grow shells and exoskeletons, a new study suggests that some species may actually benefit from increased acidity. As the ocean absorbs growing amounts of carbon dioxide from the atmosphere and becomes more acidic, not all organisms respond in the same way because they use different forms of calcium carbonate for their shells, says Justin Ries, a marine scientist at the University of North Carolina, Chapel Hill, and lead author of a study in the journal Geology. After exposing 18 marine organisms to four levels of ocean acidity — including 10 times 
pre-industrial levels — Ries found that oysters, scallops, and temperate corals grew thinner, weaker shells as acidity levels were increased. Exoskeletons of clams and pencil urchins dissolved completely at the highest levels. But some species — including blue crabs, lobsters, and shrimp — grew thicker shells that could make them more resistant to predators. It is unclear, however, whether the energy spent coping with the higher acid levels detracted from other functions, such as immune responses, Ries said. “The take-home message is that the responses to ocean acidification are going to be a lot more nuanced and complex than we thought,” he said.
A blue crab