Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs

Abstract

The reef-forming scleractinian coral, Lophelia pertusa has been recovered in bottom samples and observed as a dense debris field during remote-operated vehicle transects on a terrace on the flank of a steep-sided seamount-like knoll in the central Strait of Georgia, British Columbia. The coral debris has a minimum thickness of 33 cm and extends over several hectares in water depths of 225 to 255 m, suggesting that the coral community dominated this site for several centuries. Lophelia pertusa forms extensive reefs in many regions of the world, suggesting that a cold-water coral reef existed at this site in the recent past. This site and a sample from the west coast of Vancouver Island represent the first recognized British Columbia occurrences of Lophelia pertusa. In addition, regional multibeam surveys have revealed the presence of small (< 1 square km) Hexactinellid sponge reefs in waters 100 to 140 mdeep along the eastern approaches to the Gulf Islands in the southern Strait of Georgia in areas of low-relief glacial deposits. The surfaces of these reefs are covered with large Hexactinosidan sponges, predominately Heterochone calyx and Aphrocallistes vastus, or mantled with broken sponges where anthropogenic impacts, including trawling, have occurred. Mapping of these and other sensitive habitats will allow effective ocean management measures to be undertaken by the responsible agencies.