Research on the biology and ecology of cold-water corals (CWCs) is still in its infancy.The growth patterns of CWCs in their natural environments are poorly known. Growth rateinvestigations on these deep-sea reef builder species are needed to predict recovery timesfollowing damage to their ecosystems. This study investigates a new approach for analysingCWC growth rate, suitable for in situ application. Lopheliapertusa and Madrepora oculata (Scleractinian) were collectedfrom the Lacaze-Duthiers canyon in the northwestern Mediterranean Sea (520 m depth),marked and then either redeployed in situ for 6 months, or maintained inaquaria for growth rate comparison at a constant temperature of 13 °C, corresponding totheir habitat conditions. Two different types of staining (calcein and manganese) andthree different exposure times (30, 60 and 240 min) were tested. The results show thatcalcein offers rapid incorporation and easy detection, making it particularly suitable forskeletal growth rate investigations compared with other chemical staining. In situlinear polyp growth rates of 7.5 ± 1.2 mm y-1 and 3.5 ± 2.1 mmy-1 were measured in new polyps of L. pertusa and M.oculata, respectively. Those values were significantly higher in young polypsthan in older ones, where they decreased to 1.3 ± 1.5 mm y-1 and 1.2 ± 1.2 mmy-1. Beyond the study of coral reef growth processes, this approach offers amethodological basis for habitat quality assessment which could be used in the managementof deep-sea marine protected areas (MPA).

Lophelia pertusa, a cosmopolitan cold-water coral, offers potential for new palaeoclimate proxies. This study investigated its skeletal growth patterns to aid in this development. Corallite characteristics (calyx diameter, height, thecal width and banding) of L. pertusa sampled from oil platforms in the northern North Sea were examined. The mean distance between daughter polyps along a growth axis (27.4 ± 5 mm, SD) was equivalent to the estimated annual growth rate; hence, the polyps bud once a year. The majority of growth occurred in the first year when the characteristic trumpet shape of a corallite was formed, while the thecal wall thickened more consistently. Further examination of two polyps showed a dark growth band and centres of calcification along the full length of the inner theca, which represents early skeletal growth. Skeletal sampling adjacent to this area along sequential polyps shows promise as an annual chronology in these North Sea corals.