CONWAY, K.W.; KRAUTTER, M.; BARRIE, J.V.; WHITNEY, F.; THOMSON, R.E.; REISWIG, H.M.; LEHNERT, H.; Geological Survey of Canada – Pacific; University of Hannover; Geological Survey of Canada – Pacific; Insititute of Ocean Sciences; Insititute of Ocean Sciences; University of Victoria; University of Hamburg; : Sponge Reefs in the Queen Charlotte Basin: Deep Sea Successors to Mesozoic Reefs

In the Mesozoic Era siliceous sponge reefs became very common on the northern shelf of the Tethys Ocean where they formed a reef belt 7000 km long at the end of the Jurassic, perhaps the largest reef system to have ever developed on earth. Today hexactinellid sponge reefs exist on the deep continental shelf of western Canada in glacially scoured troughs from 165-240 m depth. The reefs occur in four complexes, with large (up to 21 m in height) bioherms and vast, low relief meadows. The largest complex is 30 km in length and 15 km wide. The massive reefs have developed over the last 9 ka on the glacially scoured, relict seabed. Development of the reef is dependent on the preferred selection of sponge skeletons by larvae as settling sites, over alternate hard substrate. Different taxa of demosponges are present, both on the reefs as individuals and also as cryptic commensal, epizootic or parasitic sponges that grow on and within hexactinosan skeletons. The sponges baffle and trap sediments from the moderate bottom currents that deliver suspended sediments and nutrients. Seasonal upwelling of nutrient rich slope waters augments shelf productivity in a silicate rich oceanic environment. The sponges form a habitat for many species of fish and invertebrates. Rockfish have been particularly identified as users of sponge habitat and rockfish catches by the deep shelf trawl fishery are often correlated with a large sponge bycatch. Bottom trawling damaged or destroyed reefs in many areas between the late 1940s and 2002, when a trawl closure was implemented.