LONG-TERM CHANGES IN POPULATION-DENSITY OF FISSURELLA-PICTA AND FISSURELLA-LIMBATA (GASTROPODA) IN THE MARINE RESERVE OF MEHUIN, CHILE

At the Marine Reserve in Mehuin, changes in density and distribution o f key-hole limpets were detected during the first five years as conseq uence of human gatherers exclusion. However, later demographic changes could be explained by within-community ecological processes, not dete cted in presence of human gatherers. Competition for food, predation a nd recruitment, were explanatory hypothesis for such changes, and they were tested at the study site for two species: Fissurella picta and F issurella limbata. At present, F. limbata does not occur at areas prot ected of the north winds, and F. picta shows a decreasing density in e xposed areas. The competition hypothesis was tested at the exposed are a through enclosure experiments. Predation over adult individuals was examined by means of a diet analysis for five predator species, from o ur data base of the Marine Reserve and other studies in that area and from other localities of the Chilean coast. Recruitment failure was st udied on a long-term basis, using data on size structure accumulated i n our data base. No inter or intraspecific competition was detected be tween the two species in the enclosure experiment, since neither speci es affected survivorship or biomass of the other. No evidence of an al ternative to man predator of adults was found, but only a very low pre dation exerted by Larus dominicanus, Sicyases sanguineus. Stichaster s triatus and Rattus rattus. A recruitment failure was detected for F. p icta at the exposed area, and we detected the entry of individuals sma ller than 30 mm during the last three years in the protected area. F. limbata recruited mainly in the exposed area. These results suggest us to evaluate the availability of suitable habitats that provide a refu ge to predation and food requirements that warrant the survival of set tlers.