Abstract
Habitat structural complexity can affect the abundance, distribution, and diversity of species. The architectural and spatial arrangement of substrate surfaces influences the availability of resources, in particular shelter from predators and environmental stresses. In communities such as the rocky intertidal zone, where shelter is a necessity, habitat complexity may directly affect population density and distribution. The invasive Asian shore crab, Hemigrapsus sanguineus, has exhibited notable success in establishing itself in the rocky intertidal zone of eastern North America, occurring in densities greater than in its native range. The present study sought to examine the influence of habitat complexity on the density of H. sanguineus. Artificial shelters of increasing levels of complexity were deployed in the intertidal zone. Results showed significant differences in crab density depending on habitat complexity, with the highest H. sanguineus densities occurring in more complex shelters, and the lowest densities occurring in less complex shelters. It was also shown that crabs exhibited shelter selectivity based on body-size. In a follow-up lab study, crab activity was observed in the presence of artificial shelters, as well as simulated tidal conditions. Shelter complexity had little influence on crab activity; instead, activity was influenced by tide conditions: crabs were more active when submerged in water than when exposed to air. These results show that crab density increases as intertidal habitat complexity increases, and may serve as a predictor of H. sanguineus density but not behavior.