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Structure-forming invertebrates belong to a polyphyletic group of primarily sessile and sedentary megafauna that can significantly enhance the complexity of physical habitats. A number of these organisms, including cold-water corals and sponges, are known to be slow growing and vulnerable to physical disturbance. In addition, as filter feeders, these invertebrates can indicate areas of consistently favorable conditions for feeding and growth. This study provides the first quantitative analysis of structure-forming invertebrate communities in many areas along the continental margin of Oregon and Washington. Geological surveys during 1992-95, using the occupied submersible, Delta, sampled an extensive area in this region, primarily on and around rock outcrops. The videos from these surveys were analyzed to inventory and catalog sessile structure-forming invertebrates and to document their associations with geological habitat types. Detailed data on geological substrate, invertebrate diversity, abundance, and density were compiled and analyzed. It was found that geological substrate and depth were reliable indicators of suitable habitat for most species included in the study. Gorgonian corals tended to concentrate in high densities in depths between 200-250m, at the southern edges of submerged rocky banks, and where hard rocky substrate was covered with a thick layer of sediment. Because of recent fishery regulation changes, this information can be used as baseline data for future studies on the effectiveness of closed areas on the recovery of structure-forming invertebrates from disturbance, particularly bottom trawling. |
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