State-dependent habitat selection by an intertidal snail: the costs of selecting a physically stressful microhabitat

Animals often modify their behavior in response to changing environmental conditions. As physical conditions become more severe animals in stressful habitats pay higher costs and should expend additional resources to search for less stressful habitats. We tested whether conditions resulting in more severe thermal and desiccation stress increased selection of more protective microhabitats by the intertidal gastropod Littorina sitkana, Philippi. We found that complex microhabitats such as barnacles and macroalgae were better on warm days because they provided cooler temperatures than less complex microhabitats such as crevices and bare rock surfaces. On warm days on the shore, snails foraged for shorter periods before selecting a microhabitat and large snails chose more complex microhabitats such as barnacles and algae more often than on cool days. We then used artificial substrates made entirely of clay in a laboratory experiment to show that this microhabitat selection by the snails was based on a preference for high topographic complexity. In this experiment snails that selected microhabitats early in the observation period chose topographically complex microhabitats significantly more often than snails that selected microhabitats late; and this became even more marked at higher temperatures. These results demonstrated state-dependent microhabitat selection by L. sitkana. The short-term cost of selecting stressful microhabitats on the shore was increased dehydration during low tide. The long-term costs of remaining in less complex areas without barnacles were lower rates of growth and survivorship. We conclude that topographically complex microhabitats allow the persistence of L. sitkana in the high intertidal zone.  1999 Elsevier Science B.V. All rights reserved.