7 A Deglacial Cold-Water Coral Boom in the Alborán Sea: From Coral Mounds and Species Dominance

The two scleractinian cold-water corals Lophelia pertusa and Madrepora oculata are widely distributed in the Alborán Sea. They have been found (alive and fossil) on seamounts, volcanic ridges and mud volcanoes, and they formed coral mounds in the geological past. While the cold-water corals show a reduced occurrence during the last glacial period, they experienced a boom since the last deglaciation until the Early Holocene. The proliferation of cold-water corals during this time is expressed in very high vertical mound aggradation rates of >400 cm kyr⁻¹. Since the mid-Holocene coral mound aggradation significantly slowed-down, which is ascribed to the reduced occurrence of cold-water corals likely supplemented by a reduced sediment supply. During the Holocene, a shift in coral species dominance towards a M. oculata-dominated cold-water coral community becomes apparent. It is speculated that in comparison to L. pertusa, M. oculata has a higher tolerance against the increasing Holocene bottom water temperatures, but is not efficient in building-up mounds likely attributed to its thinly branching framework.