Scientists have identified many benefits for restoring oyster reefs to Chesapeake Bay and other coastal ecosystems. Oysters filter and clean the water, provide habitat for their own young and for other species, and sustain both watermen and seafood lovers.

A new study from the Virginia Institute of Marine Science adds another item to this list of benefits—the ability of oyster reefs to buffer the increasing acidity of ocean waters.

Concerns about increasing acidity in Chesapeake Bay, and the global ocean, stem from human inputs of carbon dioxide to seawater—either through the burning of fossil fuels or runoff of excess nutrients from land. The latter over-fertilizes marine plants and ultimately leads to increased respiration by plankton-filtering oysters and bacteria. In either case, adding carbon dioxide to water produces carbonic acid, a process that has increased ocean acidity by more than 30% since the start of the Industrial Revolution.

A more acidic ocean concerns marine-life experts, who cite its corrosive effects on the calcium carbonate shells of oysters, clams and other molluscs, as well as its possible physiological effects on the larvae of fish and other marine creatures. At current rates of increase, ocean acidity is predicted to double by 2100.

As ocean water becomes more acidic, oyster shells begin to dissolve into the water, slowly releasing their calcium carbonate: an alkaline salt that buffers against acidity. An oyster reef is a reservoir of alkalinity waiting to happen.

The team’s calculations suggest that in 1870 – before people began large-scale harvesting of oyster meat and shells from the Chesapeake – the amount of oyster shell exposed to Bay waters was more than 100 times greater than today, with an equally enhanced capacity to buffer acidity.

“What’s worrisome about this is that the shell reservoir is getting smaller and smaller,” says Professor Roger Mann, one of the lead authors of the study. “Could we reach a tipping point where increasing acidity so overwhelms the decreased buffering capacity of dead shells that it then begins to significantly affect live oysters, further limiting their ability to add shell to the alkalinity buffer? If so, we could end up with a negative feedback loop and a worst-case scenario.”

Further Reading:
Virginia Institute of Marine Science