Fossil data links ocean acidification with mass decline of coral reefs

Ordovician fossils from Minnesota; brachiopods and bryozoans. Mark A. Wilson.Rising levels of carbon dioxide in the atmosphere are turning the ocean more acidic, threatening the survival of corals and some other marine animals. Acidic seawater impairs their ability to use calcium to build their shells and other body structures.

Millions of years ago, similar conditions may have caused major die-offs of corals and other species associated with coral reefs, according to a new analysis of geological and paleontological data appearing in the journal Global Change Biology.

The findings suggest that today’s ocean acidification could result in loss of coral reefs and numerous speciesthat live on these ecosystems.

Wolfgang Kiessling and Carl Simpson of the Leibniz Institute for Research on Evolution and Biodiversity investigated the potential linkage between ocean acidification and loss of coral reefs by using data from fossilized reefs, some hundreds of millions of years old.

Based on the PaleoReefs Database, which compiles data from some 4,000 ancient reef sites, they assessed the global volume of reefs through time.  

Their analysis revealed five episodes in the last 450 million years when global reef volume plummeted to extremely low levels.

Kiessling and Simpson determined that four of these events were correlated with periods of ocean acidification, leading them to suggest that ocean acidification and global warming could be a major cause of reef crises.

Because a decline in reef volume does not necessarily mean loss of species, the scientists also combed through the Paleobiology Database (http://paleodb.org) to identify periods of exceptionally high rates of extinction, particularly for species vulnerable to ocean acidification.

They defined vulnerable species as those that “secrete calcium carbonate skeletons or shells, lack gills, and have weak internal circulation and low metabolic rates.”

Five major extinction events emerged from the paleontological data, but not all coincided with declines in reef volume.

By examining the timing of the reef declines and extinction events, as well as the types of species affected, Kiessling and Simpson determined that two of the mass extinctions in the last 450 million years appear to have been related to ocean acidification.  

While there are inherent limitations in using geological and paleontological data to understand global biogeochemical events over periods of millions of years, this study does add weight to the idea that the current trend of ocean acidification could have dire consequences for marine life.

--by Peter Taylor

KIESSLING, W., & SIMPSON, C. (2010). On the potential for ocean acidification to be a general cause of ancient reef crises Global Change Biology DOI: 10.1111/j.1365-2486.2010.02204.x