Abstract

The spatio-temporal structure of large carnivorous decapod assemblages (minimum adult carapace width 60 mm) in the southern part of Bahía Tongoy, Chile (30°16?S 71°30?W) was analysed to understand coexistence and to investigate differential habitat use of eight species of Brachyura and one of the Stomatopoda, which occur sympatrically along the South American coast in the shallow subtidal above 25 m water depth. They form the main benthic predatory group in the sheltered areas and play a central role in the functioning of the benthic system of Bahia Tongoy, which is an important centre of the artesanal diving fishery. Crab density may be limited by the carrying capacity of the system for predatory species, thus competition for space and food may be shaping differential habitat use. A seasonal survey was carried out to describe the structure of the crab assemblage in four habitat types, including abundance and biomass distribution, species composition, and zonation. Samples were taken by SCUBA diving along transects of 100 m2 each. Although some degree of differential spatial or temporal distribution is observed, that is between major groups, not at the species level. Paraxanthus barbiger, Gaudichaudia gaudichaudii, Homalaspis plana and the stomatopod Pseudosquillopsis lessonii form a permanent group on cobblegravel grounds. These smaller xanthid species are clearly segregated from the larger Cancer porteri, Cancer coronatus, Hepatus chiliensis, and Platymera gaudichaudii, which co-occur all year round on soft sediments. Besides these two major groups, Cancer polyodon, the most abundant crab species, revealed a pattern of its own, being a habitat generalist. Lowest crab biomass was found in seagrass meadows and on sandy bottom, although both habitats serve as important refuge areas for ovigerous C. polyodon. Cobble-gravel, seagrass, and nearshore sandy areas constitute the principal nursery grounds for several crab species. Seasonal crab biomass and density variation followed different patterns in the four habitats and was driven by species-specific dynamics such as migration and recruitment.