Distribution and abundance of Rhynchocinetes typus Milne Edwards (Crustacea Decapoda), in di¡erent benthic community structures in northern Chile Luis M. Caillaux* and Wolfgang B. Stotz Universidad Cato¤ lica del Norte, Facultad de Ciencias del Mar Casilla 117 Coquimbo Chile. *Corresponding author, e-mail: lcaillau@ucn.cl An evaluation was carried out on the distribution and abundance of the rock shrimp Rhynchocinetes typus in the inshore subtidal zone on the north-central coast of Chile. A number of di¡erent benthic community types occur in the region which have di¡erent degrees of spatial complexity provided by the primary substratum and by the biotic communities colonizing the substratum. Shrimp abundance was estimated in ¢ve di¡erent community types including shallow and deep ‘barren grounds’, low encrusting commu- nities, erect suspension feeding associations, and kelp beds of Lessonia trabeculata. The abundance of shrimp was determined on three di¡erent types of primary substratum (stones, boulders, rock mass) within each community. Rhynchocinetes typus occurred in all the communities studied, showing the highest abundance on the deep barren grounds and lowest abundance on the shallow barren grounds.The shrimp was found to prefer the stony areas, as these o¡ered the greatest degree of refuge.The abundance of pre- dators was not signi¢cantly di¡erent among the di¡erent communities. However, a decline of abundance of predators was apparent over the deep barren grounds. INTRODUCTION Spatial heterogeneity of the environment may have important in£uences on predator^prey relationships. A high degree of heterogeneity may provide a greater amount of refuge which prey species may occupy in escaping predator activity (Skilleter, 1994; Beck, 1995), indirectly in£uencing the survival, distribution, and abundance of various species (Steger, 1987; Herrkind et al., 1997). Environmental heterogeneity may arise from conditions of the substrate per se, or from the biotic community inha- biting the substrate. Thus the more structurally complex communities have been observed to o¡er relatively more refuges than simpler communities, and facilitate the persis- tence of their associated species (Heck & Thoman, 1981; Marinelli & Coull, 1987; Beck, 1995). Vertically oriented species such as algae or barnacles form spatially complex (secondary) habitats which may be used as refuges for other species. Such species might not otherwise be protected on primary substrata not colonized by the habitat formers. Since the primary substratum indeed has a certain degree of heterogeneity (Bourget et al., 1994) it is therefore of some interest to compare and contrast the e¡ects of spatial heterogeneity between primary and secondary spatial structure on prey populations in marine benthic habitats. The example chosen for this study was the rock shrimp Rhynchocinetes typus Milne Edwards (1837) which inhabits the rocky subtidal of north and central Chile from the intertidal zone to 30m depth (Martinez & Arana, 1983). This shrimp inhabits a broad spectrum of subtidal commu- nities. Among these are bottoms dominated by Macrocycstis integrifolia or Lessonia trabeculata kelp, which have been gener- ally described as structurally complex and hetereogeneous, compared with so-called ‘barren grounds’ (Lawrence, 1975) which are bottoms lacking foliose algae (Woodin, 1978; Heck & Thoman, 1981; Lavalli & Barshaw, 1986; Marinelli & Coull, 1987; Wilson et al., 1987; Barshaw & Lavalli, 1988; Ojeda & Dearborn, 1989; Whale & Steneck, 1992). The rock shrimp inhabits both types of community, surviving in the presence of a number of species of ¢shes which are its potential predators (Nun‹ es, 1988; Va¤ squez, 1993; Moreno, 1972). Rhynchocinetes typus presents at least two strategies for the avoidance of predation, one of which is to carry out the majority of its life activities at night (Arana & Henriquez, 1983) when visually oriented predatory ¢shes are less active or impeded in their location of prey. During the day, when the predators are more active, Rhynchocinetes retreat to crevices or caves (Miranda & Kong, 1983) which are less accessible to the predators. Heterogeneity of com- munities and habitats present in the rocky subtidal zone suggest that the distribution and abundance of R. typus may vary from one community to another, perhaps being more abundant in communities which o¡er more complexity, and thus more possibility for refuge. Alternatively, they may prefer to inhabit communities where predator abundance is less. In order to evaluate these factors, the distribution and abundance of R. typus was determined in di¡erent commu- nities present in the rocky subtidal zone near Coquimbo. J. Mar. Biol. Ass. U.K. (2003), 83, 4112/1^9 Printed in the United Kingdom Journal of the Marine Biological Association of the United Kingdom (2003)