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

The distribution, abundance, and population characteristics of large, highl y mobile crab species (Cancer antennarius, C. anthonyi, C. productus, Loxor hynchus grandis) differed in relation to an offshore oil platform in the Sa nta Barbara Channel, California, USA. Only C, antennarius individuals recru ited onto the platform, primarily into the attached community of Mytilus ga lloprovincialis and M. californianus at depths of <12 to 15 m. The higher C PUE (catch per unit effort) of C. antennarius beneath the platform, compare d with nearby soft bottom stations, suggested that this species remained pr imarily in the vicinity of the platform. Although C. anthonyi did not recru it at the platform, adult female C. anthonyi were attracted to the platform from surrounding habitat. The higher CPUE of female C. anthonyi beneath th e platform, compared with soft bottom stations, suggested that habitat sele ction is related to reproduction in this species. C. productus and Loxorhyn chus grandis were present in low numbers at all benthic stations. The distr ibution and abundance of these crab species fit into 3 of 4 hypothesized sc enarios that described different combinations of recruitment, distribution and abundance of mobile species around oil platforms: (1) 'recruitment/emig ration', a platform provides recruitment habitat and individuals that recru it to the platform emigrate at some point to the surrounding environment, ( 2) 'recruitment/resident', a platform provides recruitment habitat, but ind ividuals remain in the vicinity of the structure (C. antennarius), (3) 'att raction', individuals that recruited elsewhere are attracted to and aggrega te at a platform (C. anthonyi), and (4) 'visitor', individuals that recruit ed elsewhere occur temporarily at the platform without aggregation (C. prod uctus, L. grandis). Our results, in the context of these scenarios, illustr ate the need to consider the responses of individual species to artificial structures.