Center for Biological Diversity

Ocean Acidification

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Last Updated November 16, 2008

Greenhouse Gas Pollution Turns the Seas Sour


National Park Service photo

Ocean acidification is one of the most pressing threats to marine ecosystems. Carbon dioxide, the most common greenhouse gas, is increasing the acidity of ocean waters, and scientists say ocean pH, a measure of acidity, is changing more rapidly than it has in 650,000 years. This occurs because when carbon-dioxide pollution is absorbed by the ocean, it causes changes in seawater chemistry. Already 50 percent of carbon-dioxide pollution from human activities has been absorbed by the ocean. The potential impacts on marine life and biodiversity are devastating.

Marine Biodiversity Threatened

Carbon-dioxide pollution threatens to decimate corals and other calcifying marine life. Rising levels of carbon dioxide in the ocean strip the seawater of important compounds needed for marine organisms to build shells and skeletons. Corals, crabs, seastars, sea urchins, and plankton will have difficulty building their protective shells in lower pH waters. Additionally, ocean acidification can dissolve the armor of many species. For example, the coral reefs that provide habitat for many marine species are likely to erode faster than they can rebuild within our lifetimes.

At the base of the marine food web are plankton, some of the most productive calcifying organisms in the ocean. According to marine scientists, calcifying plankton are vulnerable to ocean acidification and will suffer deformities and shell dissolution at levels of carbon dioxide that are likely to be reached before the end of this century. These impacts will reverberate up the food chain, affecting many other species.

Fish and other marine animals are also at risk from living in a more acidic ocean environment. Scientists warn that ocean acidification can stress marine fish and copepods, compromising their fitness and survival. In addition, stresses from ocean acidification are likely to make marine life more vulnerable to disease and less tolerant of warming waters caused by global warming.


Hawiian coral reef community. James Watt/NOAA

Imperiled Species Vulnerable to Changes in Marine Ecosystems

Due to specific habitat tolerances and needs, some non-calcifying ocean species may also become imperiled from the impacts of high concentrations of carbon dioxide. And many endangered species that depend on ocean ecosystems and are extremely vulnerable to changes in marine habitat because of already-low population numbers, will be at increased risk of extinction due to carbon dioxide pollution. Ocean acidification jeopardizes their survival.

For example, ocean acidification may dissolve the shell of the endangered white abalone, or inhibit shell formation in the first place. And of course there are numerous threatened and endangered species that prey on calcifying species, such as blue whales, humpback whales, fin whales and sea otters. Declining fitness of fish due to acidification could also impact fish-eating species such as the California least tern, California brown pelican, marbled murrelet, Steller sea lion, and Guadalupe fur seal.

Center’s Oceans Program

Ocean acidification is one of the most important threats to marine biodiversity, and the Center for Biological Diversity is using science, law, policy, and education to address the problem. The Center has recently launched an initiative to enforce carbon dioxide regulation under the federal Clean Water Act, which defines pH as a pollutant. And our lawyers and scientists are working to ensure the protection of imperiled species that are most vulnerable to changes in ocean ecosystems. A petition to protect elkhorn coral and staghorn coral under the Endangered Species Act was an early success.

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