Relatively small increases in ocean acidity significantly harm clams, bay scallops, and oysters, particularly in their crucial larval stage, according to a new study. Researchers at the State University of New York, Stony Brook, exposed shellfish to levels of acidity expected in Earth’s oceans later this century and next century, and found that modest increases in acidity led to a 50 percent decline in survival of clam and scallop larvae, reduced the size of the larvae, and caused the larvae to develop more slowly. Oyster larvae also grew more slowly, but their survival was not affected until ocean acidity reached levels expected next century. The world’s oceans absorb about half of the 30 billion tons of carbon dioxide released annually by burning fossil fuels, and the increased carbon dioxide is rapidly making the oceans more acidic, inhibiting the ability of mollusks such as clams and scallops to make their calcium carbonate shells. The researchers said the detrimental impact of ocean acidity on shellfish larvae growth rates is particularly worrisome, as the larvae are free-swimming and exposed to predation. The group’s work is being published in the journal Limnology and Oceanography.

This article originally appeared on Yale Environment 360.