Benthic invertebrate larval response to substrate characteristics at settlement: Shelter preferences of the American lobsterHomarus americanus

The factors controlling shelter selection by the first post-larval stage of the American lobsterHomarus americanus were studied in the laboratory in 1988 using an experimental approach. The relative importance of shelter size, light level within shelters, number of shelter entrances, and presence of algal-film cover in and around them were investigated. Post-larvae showed a strong preference for opaque versus transparent shelters. No difference in post-larval selectivity was observed either for shelters of different widths or heights or between shelters with different numbers of entrances. Post-larvae showed no preference for microhabitats colonized by microorganisms compared to others without colonization. The intensity of the response measured suggests a possible hierarchical organization of the different cues involved in shelter selection, the light level within the shelter apparently being the most important. Simple linear regression was used to assess the effect of shelter area on the number of post-larvae occupying a shelter. Up to four post-larvae were observed simultaneously in a shelter of 40 cm² basal area, indicating that they can cohabit at settlement. The minimum shelter area necessary to the first post-larval stage was estimated to be about 3.25 cm². The results are discussed with reference to recent hypotheses concerning the mechanisms controlling larval settlement in other benthic species with relatively weak mobility during the larval and the post-larval phases.Contribution to the programmes of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec) and of the Institut Maurice-Lamontagne