An experimental evaluation of habitat modification on species richness and abundance by enhancing spatial heterogeneity using artificial reefs was carried out in Seno Reloncaví, southern Chile (41°29′S, 72°54′W). Because of the potential applications of artificial
reefs for fisheries, particular attention was paid to commercially valuable species. In October 1990, hollow (30 cm)3 concrete blocks with 20 cm diameter openings on their six sides were arranged in two layers to form 0.6 m high reefs of 0.81 m2 basal area. Five of these
reefs were deployed at depths of 13 to 18 m on sandy and rubble bottoms. Colonization and community development was quantitatively recorded using SCUBA. Three major faunal groups—fish, crustaceans, and sea urchins—increased their abundance on the reefs. Commercially valuable species
included adults of two crabs: Cancer edwardsi and Homalaspis plana. The reefs also served as recruiting sites for juvenile rockfish (Sebastes capensis) and as feeding and courtship arenas for tripterygids (Tripterygion cunninghami). A few other crab and fish species
also appeared in and around the reefs but without becoming residents. Algal colonization was slow and their abundance was notably controlled by sea urchins (Arbacia dufresnei). Artificial habitats placed on low-relief bottoms of the Channel Region of Southern Chile can potentially enhance
the abundance of some commercially valuable species. The effect of artificial reefs on species richness (especially fish) was not striking, however. This is most likely related to a natural paucity of species in the region.
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