Sollfrank, Nicole (2011) The combined effect of variable food supply and elevated CO2 partial pressure on feeding and calcification rates of the Mediterranean cold-water coral. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 104 pp.

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Abstract

Only 50 % of today's anthropogenic C02 emissions stay in the atmosphere, while 25 % are absorbed by the world's oceans. The complex reactions of seawater with C02 cause fundamental changes to seawater carbonate chemistry, which already led to a decline in seawater pH by 0.1 units since pre-industrial times. Another consequence of the so-called "ocean acidification" (OA) is a decreasing seawater saturation state with respect to aragonite (Qar)- the material from which skeletons of scleractinian corals are built. Twenty-six individuals of the Mediterranean cold-water coral Madrepora oculata were incubated under two different feeding regimes, with the high (HF), respectively low feeding (LF) corals receiving freshly hatched Artemia nauplii five, respectively two times a week. To investigate the effects of OA on the corals, the animals were subsequently exposed to pC02 regimes of 380 (ambient pC02), 1600, 800, 2000 and 380 ppm for two weeks each. After each exposure, the corals were incubated in a closed system for 18 hours, followed by the measurement of the coral calcification rates (G) with the total alkalinity anomaly technique (G-TA). Additionally, G was determined with the buoyant weighing technique (G-bw). Every second week, POC and PON ingestion of the corals was measured. Feeding rates on POC were PON significantly affected by high pC02 conditions, with the lowest ingestion rates found at 2000 ppm for both feeding groups. Average G-TA was negative for 1600 and 2000 ppm and positive for ambient pC02 and 800 ppm, whether or not feeding regime was considered in the analyses. As seawater was under-saturated with respect to aragonite (Qar < 1) in the two highest pC02 treatments, this suggests a strong dependence of coral calcification on nar· The effect of pC02 on G-T A was highly significant (repeated measures ANOVA, p << 0.001), while G-bw was not significantly affected by pC02. A significant effect of the feeding regimes on G was not detected, either. However, the lowest, respectively highest feeding and calcification (G-TA) rates were found at 2000, respectively 800 ppm. This might indicate that Madrepora oculata exposed to medium pC02 ("medium" defined as 800 ppm in this study) is able to compensate for the effects of OA by an additional energy supply obtained from heterotrophic feeding. Another explanation might be a general insensitivity of Madrepora oculata to medium pC02. In either case, the corals most likely could still endangered by OA, as food concentrations in the oligotrophic Mediterranean Sea are low and pC02 could further rise to 1900 ppm by the end of the 23rd century.

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