Invertebrate Species Richness on Deep Cobble and Gravel Bottoms off Cape Arago, Oregon

Although conservation of marine diversity is a major goal of an ongoing process to establish marine reserves in the Oregon Territorial Sea, virtually all subtidal studies off Oregon have considered only fishes and the largest invertebrates. Using dredge samples, we assembled comprehensive species lists of sessile and motile invertebrates on cobble and gravel substrata between 50 and 70m depths off Cape Arago, Oregon. The species richness on cobble substratum (112 species) was much higher than species richness on gravel sub- stratum (31 species). Species accumulation curves suggest that we found most of the species on the cobble substratum but that more samples would be required to fully assess the cobble community. Sessile invertebrates were more common than mobile invertebrates. The data also showed significant patchiness, as indicated by between-sample differences. This study shows that sea-floor mapping that does not resolve substratum particle size cannot be used to predict richness of the rocky-bottom community.