Acid in Coastal Waters Affecting Marine Animals

High levels of acid in coastal waters could soon prevent marine creatures from forming and keeping their shells, says a new study led by University of Georgia researchers.

Their findings were recently published in the Nature Geoscience. According to the study, the combined effects of excessive atmospheric carbon dioxide from burning fossil fuels and high levels of fertilizer dissolved in the Mississippi River are leading to an unexpectedly large increase in the acidity of subsurface water in the northern Gulf of Mexico.

“Before, scientists only worried about low oxygen in waters along the coast,” said Wei-Jun Cai, a professor of marine sciences at UGA. “Our paper basically says not only do we need to worry about low oxygen, we also need to worry about acidification.”

When fertilizer-polluted river water flows into coastal waters, phytoplankton growth explodes. And, after dying, this excess plankton sinks to the sea bottom and decomposes. The result is a release of massive amounts of carbon dioxide and a decrease in the amount of oxygen in the water.

Moreover, this dissolved carbon dioxide forms great quantities of acid in the water. This acid dissolves the shells and skeletons of sea animals. Absorption of carbon dioxide produced by fossil fuels also increases the ocean’s acidity.

Sea creatures are less able to form and maintain shells or skeletons as the water becomes more acidic. Cai and his coauthors predict that many will no longer be able to form such structures by the end of the century if coastal water acidity keeps increasing (which means they would go extinct).

“Many of our fisheries resources, especially shellfish, are concentrated in areas where rivers discharge onto the coast, like the northern Gulf and the East China Sea, and thus are at risk,” said UGA marine sciences professor James T. Hollibaugh, who collaborated with Cai on the project. “And of course there are likely ramifications for fish and animals further up the food chain that depend on these same shellfish for food.”

The study found similar results for coastal waters adjacent to the mouth of the Yangtze River, the largest river in China. This finding suggests the double whammy of fertilizer and fossil fuel pollution is damaging marine ecosystems worldwide.

To reduce future damage to the coastal environments, Cai and his colleagues say that farmers will need to improve management of fertilizers use and national governments will have to place legal limits on fossil fuel use.

More information about ocean acidification >>