Abstract
back to Publications Conway, K.W., Barrie, J.V. & Krautter, M., (2007): Complex deep shelf habitat: sponge reefs in the Pacific Northwest.
Complex deep shelf habitat: sponge reefs in the Pacific Northwest
Abstract: Siliceous (hexactinellid) sponges form reefs that cover large areas of the seafloor, and are a complex habitat that may be stable for millennia. Hexactinosidan sponges construct framework reefs between 90 and 240 m of water to form distinctive biological communities dominated by a low-diversity assemblage of glass sponges that support a diverse community of other species. The hexactinellid sponge reefs were first discovered during surveys employing sidescan sonar and sub-bottom profiling systems in the mid 1980s. High-resolution, deep-towed, single-channel seismic (Huntec Deep-Tow), conventional hull-mounted profilers, sidescan-sonar instruments, and multibeam swath bathymetry systems have all been used to map sponge reef distribution. Four extensive sponge reef complexes, discontinuously covering over 1000 km2, have been identified in the Queen Charlotte Basin, and recently eight smaller reefs have been discovered in the Georgia Basin. The acoustic signature of these features, which can attain heights of 21 m, is distinctive and readily identified. The reefs develop from the coalescence of small mud mounds that grow, over millenia, to form steep-sided bioherms and really extensive biostromes. The acoustic properties of the reefs are mainly due to the non-reflective, massive clay matrix, the framework of buried siliceous sponge skeletons, and the surface covering of living sponges. These characteristics provide a sharp acoustic contrast with the normally reflective and dense underlying relict glacial sediments, which are characterized by gravel to boulders, and glaciomarine clays that have been scoured by icebergs. This difference provides a distinctive backscatter contrast in multibeam datasets that can readily be used to map reef distribution.