For over a decade, scientists have been scratching their heads over why shellfish populations on the East End of Long Island have not rebounded from brown tide outbreaks that occurred decades ago.

A study by two researchers from the Stony Brook University School of Marine and Atmospheric Sciences may have found the main culprit: carbon dioxide.

With carbon dioxide emissions, the majority of focus has gone towards the rising concentration of this gas in the atmosphere and the climatic implications of this rise.  However, the impact of these emissions on the oceans may be on par with those on the climate.  According to the Southampton Press, about half of the carbon dioxide emissions released by humans is absorbed by the oceans.

Once absorbed by the oceans, the added carbon dioxide increases the acidity of the water.   Doctoral candidate Stephanie Talmage and Dr. Christopher Gobler, a marine science professor, have been studying the impact of this process, also known as ocean acidification, on shellfish survival rates.  Over the past year, the two have been raising larval shellfish under a wide spectrum of carbon dioxide levels that simulate past, present and future pH levels of ocean water.

The survival rates under pre-industrial conditions have been between 70-80 percent, but drop to 20 percent under conditions expected at the end of this century.  The mechanism behind the decline, according to Dr. Gobler, is the impact of the pH on carbonate, a critical component to the shells of scallops, lobsters and shrimp.  As the ocean becomes more acidic, the carbonate levels decrease and cause shell thinning.