Effects of an offshore oil platform on the distribution and abundance of commercially important crab species

The distribution, abundance, and population characteristics of large, highly mobile crab species (Cancer antennarius, C. anthonyi, C. productus, Loxorhynchus grandis) differed in relation to an offshore oil platform in the Santa Barbara Channel, California, USA. Only C, antennarius individuals recruited onto the platform, primarily into the attached community of Mytilus galloprovincialis and M. californianus at depths of <12 to 15 m. The higher CPUE (catch per unit effort) of C. antennarius beneath the platform, compared with nearby soft bottom stations, suggested that this species remained primarily in the vicinity of the platform. Although C. anthonyi did not recruit at the platform, adult female C. anthonyi were attracted to the platform from surrounding habitat. The higher CPUE of female C. anthonyi beneath the platform, compared with soft bottom stations, suggested that habitat selection is related to reproduction in this species. C. productus and Loxorhynchus grandis were present in low numbers at all benthic stations. The distribution and abundance of these crab species fit into 3 of 4 hypothesized scenarios that described different combinations of recruitment, distribution and abundance of mobile species around oil platforms: (1) 'recruitment/emigration', a platform provides recruitment habitat and individuals that recruit to the platform emigrate at some point to the surrounding environment, (2) 'recruitment/resident', a platform provides recruitment habitat, but individuals remain in the vicinity of the structure (C. antennarius), (3) 'attraction', individuals that recruited elsewhere are attracted to and aggregate at a platform (C. anthonyi), and (4) 'visitor', individuals that recruited elsewhere occur temporarily at the platform without aggregation (C. productus, L. grandis). Our results, in the context of these scenarios, illustrate the need to consider the responses of individual species to artificial structures.