Ocean Acidification

Increasing pCO2 in the atmosphere results in ocean acidification. The changes in ocean chemistry posed by such phenomenon pose an imminent threat to calcifying organisms such as cold-water waters corals. Very little information is available on the effect such threat poses on cold-water corals, particularly in the Mediterranean frontier. Three species of Mediterranean cold water corals (Lophelia pertusa, Madrepora oculata and Desmophyllum sp) were exposed to ocean acidification conditions. Four separate pCO2 treatments were represented: 412 ± 73 ppm, 497 ± 117 ppm, 665 ± 100 ppm, and 866± 191 ppm. Coral response was measured using several methods of assessing growth: buoyant weight, colour (area) projection, new polyp development, and skeletal density. Response to ocean acidification was shown to be species specific with Lophelia pertusa being generally more affected (a reduction of over 40% buoyant weight per day on higher pCO2 compared to lowest pCO2) than Madrepora oculata. Growth rate was not clearly influenced by ocean acidification in Desmophyllum sp. After 9 months of experiment, polyp development and skeletal density were not significantly altered by ocean acidification. A reduction in projected colour (area) was observed for both Madrepora oculata and Lophelia pertusa area under medium and high ocean acidification scenarios (Madrepora oculata over 50% colour (area) per day on higher pCO2 compared to lowest pCO2 ; Lophelia pertusa nearly 50% colour (area) per day on higher pCO2 compared to lowest pCO2). Response of the three species assessed was not linear, possibly due to several sources of variation interacting with acidification. That Lophelia pertusa consistently performs better at lower acidification scenarios has implications for the future of the deep-sea coral community and species associated. More studies are needed to assess whether the response observed here is consistent across other sites and cold-water species.

Berzunza Sanchez M. M., 2011. Growth of threee species of Mediterranean cold-water corals exposed to ocean acidification. Master thesis, Christian-Albrechts-Universität, Kiel, Germany. Master thesis.