In the past century, the oceans absorbed almost half of the atmospheric carbon dioxide derived from human activities like the burning of fossil fuels. As the ocean absorbs carbon dioxide, it becomes more acidic and has a lower concentration of carbonate, the substance which shell-making organisms use to produce their calcium carbonate structures, such as their shells.

Talmage and Gobler examined the growth and survival rates of larvae from three species of shellfish. The larvae were raised in containers bubbled with different levels of carbon dioxide in the range of concentrations projected to occur in the oceans during the 21st century and beyond. Under carbon dioxide concentrations estimated to occur later this century, the clam and scallop larvae showed a more-than-50% decline in survival. The larvae were smaller and took longer to develop into the juvenile stage. Oysters also grew more slowly, but their survival was only affected at carbon dioxide levels expected next century.

"The longer time spent in the larval stage is frightening on several levels," said Talmage. "Shellfish larvae are free swimming. The more time they spend in the water column, the greater their risk of being eaten by a predator. A small change in the timing of the larval development could have a large effect on the number of larvae that survive to the juvenile stage and could dramatically alter the composition of the entire population."

The researchers hope their work might help improve the success rate of shellfish restoration projects. "On Long Island, there are many aquaculturists who restock local waters by growing shellfish indoors at the youngest stages and then release them in local estuaries," said Talmage.

"We might be able to advise them on ideal carbon dioxide conditions for growth while larvae are in their facilities, and offer suggestions on release times so that conditions in the local marine environment provide the young shellfish the best shot at survival."