| Summary: | Only few cold-water coral species are able to build reef-like structures in the deep oceans. These deep coral bioherms are likely among the first to be affected by ocean acidification i.e. decrease in pH due to an increase in pCO2. Calcification rates of L. pertusa were assessed for Skagerrak and Mingulay corals and the response in calcification to lowered pH has been investigated for Skagerrak L. pertusa during 2 research cruises. Experiments were carried out directly onboard using freshly collected corals. Calcification rates were assessed using the 45CaCl2 labelling technique under ambient pH and pH lowered by 0.15 and 0.3 units. Calcification rates were on average 0.07% d-1 ±0.02 S.E. and 0.05% d-1 ±0.01 S.E. (normalised to initial skeletal weight) for bulk calcification of small branches of Mingulay and Skagerrak corals, respectively. Highest calcification rates were found in youngest polyps. Lowering the pH by 0.15 and 0.3 pH units reduced coral calcification by 30 % and 56 %, respectively. Also, the effect of changes in pH (0.3 pH units lower than in ambient water) on calcification rate was stronger for fast growing, young polyps (59 % reduction) than for older polyps (40 % reduction). This first study on calcification rate and pH effects for L. pertusa implies that the young and fast calcifying corallites will be influenced most negatively by ocean acidification. Laboratory experiments on Mediterranean cold-water corals are presently underway and corals are studied under variable pCO2 and temperature range. The alkalinity anomaly technique is used to assess calcification rates and results will be compared with findings of Skagerrak and Mingulay L. pertusa Peer Reviewed
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