Indirect Effects of Human Exclusion from the Rocky Intertidal in Southern Chile: A Case of Cross-Linkage between Herbivores

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Abstract
Differences in size structure of the limpet Siphonaria lessoni in different localities have been related to variations in density of the key-hole limpet Fissurella picta under the supposition that they compete for food. Here, we test the hypothesis that the human exploitation of F. picta is responsible for changes in the individual growth rate of S. lessoni. Removals of F picta before the springtime period of recruitment produced greater availability of algae in the rocks. Analysis of monthly size frequency distributions of S. lessoni cohorts recruited into these experimental zones were compared with other obtained in areas with natural densities of F. picta. In the presence of F. picta, S. lessoni''s individual growth rate decreased; also, fecundity decreased near to 38% because individuals of the same age are smaller.