Mapping Cold-Water Coral Reefs with Multibeam Echosounder Bathymetry and GIS Technology

The Sula Reef on the Mid-Norwegian shelf is the world's largest cold- water coral (Lophelia Pertusa) complex. Multibeam swath bathymetry mapping of the sea bottom has revealed that this reef at 300 m water depth is 13 km long and 400 m wide, and is composed of ca. 500 individual coral mounds. The substrate of the reef consists of dipping Mesozoic sedimentary rocks, overlain by Pleistocene glacial deposits. Shaded relief images demonstrated the irregular seabed with numerous glacial flutes and iceberg plough marks. The locations of the coral mounds are preferentially on the ridges of the flutes and on the flanks of the plough marks. Appling the methodology that was used and tested during the Sula Reef study, an area of previously undiscovered coral reefs was found in 2000. Multibeam swath bathymetry data indicated the occurrence of spectacular, up to 40 m high coral mounds on the flanks of the 100 m high moraine ridge in 300 m water depth, ca. 100 km off-shore northern Norway. The reef interpretation was later confirmed by the under water video inspection showing abundant corals on the mounds. It is interesting to note that coral mounds occur exclusively on the flanks of the moraine ridge while they are absent on the top of the ridge, or on the surrounding flat, muddy sea bottom. The knowledge from such coral reef projects is compiled into a national methodology project aiming at habitat mapping (SUSHIMAP - Survey strategy and methodology for habitat mapping). Relying heavily upon multibeam and GIS techniques, this 4-year project shall define a procedure for seabed habitat mapping, including cold-water coral reefs, on the Norwegian shelf and a long-term plan for monitoring of marine habitats.