Caribbean gorgonian corals highly resistant to ocean acidification

Recently a group of coral scientists found that Caribbean gorgonian corals could calcify and grow under future ocean acidification scenarios. The finding, just published in the online first version of the journal Coral Reefs, has important implications for predicting the abundance and composition of the future coral reef community under the “business as usual scenario”.

Increases in atmospheric carbon dioxide concentrations are altering the seawater chemistry of the ocean, lowering the pH and causing the ocean to become more acidic. This has serious effects on the calcification rates of many different marine organisms, with negative repercussions to the ecosystem. Marine animals with calcified shells and skeletons, such as corals, mollusk, clams, urchins, and crabs, among others, will struggle to keep their natural protection.

Despite the high relative abundance of gorgonian corals (including seafans, sea whips, sea candelabra and sea rods) at both sides of tropical and sub-tropical America, the Mediterranean Sea and the west coast of Africa, it is surprising how little we know on their ability to calcify in response to stressors such as ocean acidification.

It is believed that corals with calcareous skeletons formed by high-magnesium calcite, such as tropical gorgonians, can be more susceptible to carbonate ions depletion than either calcite or aragonite-depositing organisms. However, no studies on these organisms were available until now.

A collaboration of scientists from BIOMMAR at Universidad de los Andes (Bogotá, Colombia), Smithsonian Institution (Fort Pierce) and University of Miami (RSMAS), investigated the calcification response of Eunicea fusca, an abundant tropical shallow-water gorgonian coral typical of Caribbean coral reefs (see photo above), under different experimental concentrations of CO2 that simulated a range of predicted future ocean acidification conditions. The authors measured growth and calcification response in a range of CO2 concentration from 285 to 4585 ppm (pH range 8.1 – 7.1).

First author of the study, graduate student Carlos Gómez said “although Eunicea fusca showed a negative response for calcification and CO2 concentrations; growth and calcification did not stop in the different CO2 treatments that were used in the study, which spanned a wide range of concentrations. Having the ability to work with such a wide range of CO2 concentrations, I think was one advantage of our study”. These results suggest that this species, although affected by high levels of CO2, could thrive in mid-term ocean acidification conditions expected by the end of this century, and allow us to predict the future of diversity in reef communities at a time of increasing ocean acidification.

This study is the first to report the effects of future ocean acidification on a tropical shallow-water gorgonian coral, which shows some degree of resilience to elevated concentration of CO2.

Juan Armando Sanchez, Frontiers, 4 December 2014. Article.

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