Spatial distribution of the intertidal limpet Patella depressa Pennant, 1777: Patterns across wave exposure and season

Spatial patterns of intertidal rocky shore gastropods depend on various environmental stresses and biological interactions. Understanding how and why these patterns arise can provide important insights into the ecology and behavior of ecologically key organisms. Here, we addressed the unexplored limpet aggregative behavior and the influence of wave action and season. We assessed intraspecific patterns of the spatial distribution of Patella depressa on rocky shores of contrasting wave exposure in seasons with different levels of storminess in central Portugal. We predicted that intraspecific spatial structure estimated through individual-to-individual nearest neighbor distances (NNDs) would be more aggregated on exposed sites than on sheltered sites and, if season-dependent, such aggregation would be greater during the stormier winter months. Two sheltered sites and two exposed sites were sampled three times in winter and in summer. On each sampling occasion, the mean NNDs were measured digitally in 20 replicated random quadrats (0.25 × 0.25 m). We showed that season and exposure significantly affect the spatial distribution of limpets, with an aggregated spatial structure on exposed sites during the stormy winter months. On sheltered sites, limpets were randomly distributed regardless of season. In contrast, on exposed sites, limpets which were randomly distributed during summer changed to an aggregated structure in the winter. This is the first report of seasonally modulated patterns of spatial distribution associated with wave exposure for P. depressa. Such behavior can influence resource availability and outcomes of competitive interactions, with implications for ecosystem functioning.