Extra Carbon Dioxide Bulks Up Lobsters

Rising levels of atmospheric CO₂ may lead to larger lobsters, shrimp, and crabs, but this change is more likely to disrupt ocean food webs than to benefit seafood buffets, according to a study by Justin B. Ries of the University of North Carolina, Chapel Hill, and colleagues (Geology 2009, 37, 1131). Some of the additional CO₂ has been sinking into the world’s oceans, dropping the water’s pH by 0.1 units. Ries and coworkers decided to check out how this ocean acidification might alter the shells of 18 marine organisms, and they found that the effects were more varied than expected. The calcium carbonate shells of 10 creatures, such as sea urchins and clams, began to diminish when exposed to more acidic conditions. But other creatures, including lobsters, bulked up. The different reactions to acidification could reflect differences in how the organisms regulate pH, or whether their outer shell layer is protected by an organic covering, Ries notes. Because both carbonate winners and losers are part of the same food web, creatures that could stand to benefit by bulking up may find themselves with too little to eat and may not prosper after all, the researchers suggest.