Development of coral banks in Porcupine Seabight: do they have Mediterranean ancestors?

Abstract

This paper presents an overview of the spatial distribution and morphology of coral banks in the Porcupine Seabight in relation to their environmental settings. The study area is characterised by well-delimited clusters of coral banks, each featuring typical bank morphology and environmental setting. In the central part of the basin, two mound provinces can be identified: a set of complex flat topped seafloor mounds in the Hovland Mound province is flanked to the north by a crescent of numerous north-south elongated buried coral banks in the Magellan Mound province, along the eastern margin of the basin partly buried and seabed coral banks represent the Belgica Mound province. The banks are mound-shaped elevations, many of them hosting living deep-water corals (Lophelia pertusa, Madrepora oculata, Desmophyllum cristagalli, Dendrophyllia sp.) and associated fauna. This active biological layer covers a dead assemblage of corals clogged with mud. All coral banks, buried or seabed, occur in association with current-induced features (e.g., scouring features, dunes) and steep palaeo- and present-seabed slopes. Only a few banks have a present-day seabed expression, which suggests that environmental conditions have been more favourable for bank development in the past. The depth range of the seabed coral banks coincides with the Mediterranean Outflow Water which may control indirectly the coral distribution. The distribution of corals in the southern part of the North Atlantic and the actual link with Mediterranean water suggest a possible migration of corals within the Mediterranean water along the NE Atlantic margin. The start-up phase of the coral bank development in the basin has taken place simultaneously for all provinces, and tentatively framed in times subsequent to a Late Pliocene period of erosion and non-deposition. It is considered that the sedimentary load of the currents plays an important role in the bank development. Coral banks accrete by the active baffling of sediment by the biological framework and growth of the biological cap. When sedimentation and biological growth get out of balance, the framework will progressively be clogged with sediment. Once sediment dominates the structure the coral banks get buried and draped by sediment.