Threat : Ocean Acidification

Ocean chemistry is changing, and the main focus of attention has been ocean acidification, which occurs when increased CO2 uptake reduces available carbonate ions . Recent projections suggest, under high emission scenarios, that global average pH could decrease from 8.1 to 7.8 by the end of the century. However, ocean acidification hotspots (acidity increasing at a faster rate) occur due to regional factors such as coastal upwelling, changes in discharge rates from rivers and glaciers, sea ice loss, and urbanization.

Ocean acidification is a significant threat to shellfish. The United States the shellfish industry may be losing more than $400 million a year by 2100 as a result of ocean acidification. Acidic ocean waters can inhibit shellfish growth, lower survival rates, and populations. For example, in Chesapeake Bay increased growth rates in crabs, tied to lower pH, can lead to increased predation of oysters. Recent studies suggest that competitive interactions among species may shift, putting shellfish at a relative disadvantage.

According to a 2019 report prepared by a Massachusetts Special Legislative Commission on Ocean Acidification, the Commonwealth is home to some of the most acidification-vulnerable communities in the country. 

Oysters are a habitat forming species. If they are harmed by ocean acidification (and pathogens), key habitat may be lost for other species and ecosystem services may be disrupted. For example, oyster reefs can also provide storm surge protection, and their loss can make shorelines more vulnerable to coastal erosion and damage.

Despite Wellfleet Bay’s high rate of primary production, it may be particularly sensitive to the acidification of coastal waters because of anthropogenic disturbance to its fringing salt marshes. About half the coastal marshes around Wellfleet Harbor have been diked and drained since 1909. Salt marsh diking and drainage generates acid sulfate soils and the leaching of low-pH freshwater during ebb tides into the harbor

Ocean Acidification Impacts Relevant to Shellfishing

1. A decline in calcification rates, leading to slower lipid accumulation rates and thinner, malformed, or eroded shells.
2. Acidification may favor predators feeding on bivalves.
3. Acidification may cause a decrease in populations of bivalve species, by potentially inhibiting larval development.

“Oyster farmers and ocean acidification in Washington State”