Patterns of shell utilization by hermit crabs as a proxy of gastropod population dynamics

Abstract

Hermit crabs are known to use empty gastropod shells, which allows them to grow and avoid predation and desiccation stress. However, shell benefits lessen with crab growth and natural damages so that hermit crabs are always in search for new and better-quality shells. This makes these organisms dependent on the input of newer shells, presenting adaptations to locate new released shells, as perception of chemical cues liberated by predated gastropods. The allocation from older to newer shells suggests that the patterns of shell utilization by hermit crabs may reflect populational changes of gastropod species. In this scenario, we aimed to investigate whether a recognized population decline of the intertidal gastropod Olivella minuta in summer can be explained by mortality or intertidal migration. To do so, we analysed patterns of shell availability and use (number and quality) by hermit crabs before and after the population decline. Contrary to our mortality hypothesis, there was no increase in availability and occupancy of newer shells in the area, as well as no increase in shell quality after the period of population decline of gastropods. There were also no general changes in the size distribution of available and occupied shells. Thus, it is likely that O. minuta migrates towards lower areas of the intertidal to avoid thermal stress and mortality due to summer higher temperatures