New research by an international team of oceanographers has found that ocean acidification has significantly compromised 40% of the global surface ocean, and 60% of the subsurface ocean to a depth of 656 feet (200 meters).
This extent of acidification indicates there has been considerable declines in suitable habitats for important marine species that rely on dissolved calcium and carbonate ions to build their hard shells and skeletons. Impacted economically and ecologically important species include crabs, oysters, mussels and other bivalves, corals and small sea snails known as pteropods that form the base of food webs.
The finding by an international team that included scientists from Plymouth Marine Laboratory in Great Britain, NOAA’s Pacific Marine Environmental Laboratory, the Cooperative Institute for Marine Ecosystem Research at Oregon State University, and the Earth System Science Interdisciplinary Center at the University of Maryland, was based on a detailed analysis of ocean carbon system observations, models and biological assessments. The research was published in the journal Global Change Biology as “Ocean Acidification: another planetary boundary crossed”.
The new analysis provides a global assessment of the saturation state of a form of the mineral aragonite. Aragonite is a form of calcium carbonate that calcifying marine organisms like corals and shellfish use to build their shells and skeletons. NOAA uses aragonite saturation state as a measure of how easily aragonite will dissolve in seawater, in order to track ocean acidification. As pH levels drop, causing seawater to become more acidic, calcifying species struggle to maintain their protective structures, leading to weaker shells, and slower growth. In 2016, NOAA research linked carbon dioxide (CO2) to dissolving sea snail shells off U.S. West Coast, reduced reproduction and decreased survival rates.
“Our research has found that since the pre-industrial era, the aragonite saturation state has declined by a fifth in 40% of surface waters and in 60% of subsurface waters to a depth of 200 meters, which means that we have gotten close to or crossed the boundary of ‘safe living space’ of good habitats for some calcifying species in many regions of the ocean,” says Richard Feely of NOAA’s Pacific Marine Environmental Laboratory.
The largest change in surface waters has been in the polar regions like Alaska and the Arctic, while the largest change in deeper waters has been in the sub-polar regions and along the west coast of North America from Canada to Mexico.
Read about NOAA’s research in U.S. regions.
The researchers estimate that some tropical and subtropical coral reefs have lost 43% of their suitable habitats. Additionally, sea butterflies as an important food web plankton in polar regions have lost up to 61% of their habitat. Of particular economic importance, coastal shellfish species have lost 13% of their global coastline habitats compromising essential biological processes.
NOAA’s Ocean Acidification Program supported the work by researchers at the NOAA Pacific Marine Environmental Laboratory.
More documented effects of ocean acidification
Additional findings of a NOAA study published in February 2025 in the Canadian Journal of Fisheries and Aquatic Sciences show correlations between changes in ocean pH in the Bering Sea and recent declines of Bristol Bay red king crab. The study led by Mike Litzow at NOAA’s Alaska Fisheries Science Center Kodiak Lab, looked at whether increased acidity, sea ice, or warming could explain the decline in southeast Bering Sea red king crab. Results demonstrated the first correlation between ocean acidification with declines in a wild stock. Increasing acidity explained about 21% of the population decline over the 1980 to 2023 period, and roughly 45% of the decline since 2000, the study found. Litzow and his co-authors note that the study shows a correlation, and that it’s very difficult to apply lab-based results on wild populations because ecosystems are complex.
The Bering Sea red king crab fishery experienced a two-year closure from 2022 to 2024 due to low stock abundance, and reopened in October 2023 with a significantly reduced quota.
In 2020, a NOAA study, led by Nina Bednaršek of Oregon State University, documented for the first time that ocean acidification along the U.S. Pacific Northwest coast is impacting the shells and sensory organs of some young Dungeness crab, another prized crustacean that supports the most valuable fishery on the West Coast.
In the late 2000s, changing ocean chemistry rocked shellfish hatcheries in the Pacific Northwest, driving an estimated $110 million loss for the industry until hatchery managers began to buffer the water used in their tanks. to adjust the pH.
