Ocean Acidification

Ocean acidification caused by increased atmospheric CO2 is feasible threat for calcifying organisms including corals. Decalcification by lower pH has been reported in several marine organisms, such as foraminifera, sea urchin and corals. In order to evaluate the impact of lower pH on calcifying organisms, the range of tolerable pH on their various life stages should be investigated. In addition, study on variation of chemical compositions in calcifying organisms against pH is important to understand the mechanism of biomineralization for each organism.
In this study, we assessed the effects of increased CO2 on early life stages of scleractinian corals (Acropora spp.), which is one of the most dominant species around Okinawa Island, Japan. In this experiment, four steps of pH (SWS) were controlled using filtered seawater which was bubbled by pure CO2 at 27 oC (pH 6.6, 7.3, 7.6 and 8.0). Approximately 40 coral polyps were cultured more than 10 days under each pH setting and several polyp skeletons were weighted one by one using a microbalance. Then trace elements (Mg/Ca, Sr/Ca, Ba/Ca and U/Ca) in polyp samples were measured by ICP-MS (HP4500). As a result, smaller polyps were found at lower pH, indicating a positive relation between polyp growth and pH. However, even at pH 7.3, which is under-saturation for aragonite, skeletons were not dissolved and/or grown slightly. It is suggested that a specific physiochemical mechanism may control pH in the coral. Furthermore, as previous studies suggested, Mg/Ca in coral skeletons seem to be controlled by coral growth and it could play important role on coral biomineralization.



Inoue M, Suwa R, Iguchi A, Suzuki A, Kawahata H & Sakai K, 2009. Assessment of increased CO2 on growth and variation of trace elements of the coral polyp skeletons (Genus Acropora). Awards Ceremony Speeches and Abstracts of the 19th Annual V.M. Goldschmidt Conference, V.M. Goldschmidt Conference. Geochimica et Cosmochimica Acta 73(13)-1:A570. Supplement.