This is an excerpt from a piece in the New York Times Science Section.
Different species of oyster Phroto Credit Tony Cenicola/The New York Times
By studying oyster populations in relation to acidity levels, a team of researchers has concluded that oysters — particularly their shells — can play a significant role in reducing that acidity.
“Oyster shells are made out of calcium carbonate, so they’re sort of like an antacid pill,” said George Waldbusser, an assistant professor of earth, ocean and atmospheric sciences at Oregon State and an author of the study, which appears in the journal Ecology. “In an undisturbed oyster reef, healthy oysters are generating a lot of biodeposits,” a genteel term for excrement, “which helps generate CO2 to help break down those shells, which helps to regenerate the alkalinity back into the environment.”
Since the Industrial Revolution, ocean acidity has increased by about 30 percent, researchers say, and it is on track to double by 2100. Among the dangers of highly acidic waters are damage to fish larvae and corrosion of mollusk shells, which means the oysters in this case are helping themselves. “It creates a positive feedback loop,” Dr. Waldbusser said.
Here is the abstract from the study.
Disease, overharvesting, and pollution have impaired the role of bivalves on coastal ecosystems, some to the point of functional extinction. An underappreciated function of many bivalves in these systems is shell formation. The ecological significance of bivalve shell has been recognized; geochemical effects are now more clearly being understood. A positive feedback exists between shell aggregations and healthy bivalve populations in temperate estuaries, thus linking population dynamics to shell budgets and alkalinity cycling. On oyster reefs a balanced shell budget requires healthy long-lived bivalves to maximize shell input per mortality event thereby countering shell loss. Active and dense populations of filter-feeding bivalves couple production of organic-rich waste with precipitation of calcium carbonate minerals, creating conditions favorable for alkalinity regeneration. Although the dynamics of these processes are not well described, the balance between shell burial and metabolic acid production seems the key to the extent of alkalinity production vs. carbon burial as shell. We present an estimated alkalinity budget that highlights the significant role oyster reefs once played in the Chesapeake Bay inorganic-carbon cycle. Sustainable coastal and estuarine bivalve populations require a comprehensive understanding of shell budgets and feedbacks among population dynamics, agents of shell destruction, and anthropogenic impacts on coastal carbonate chemistry.