Is there variation in the occupation of Gastropoda shells and in the diurnal and nocturnal activities of the hermit crab Dardanus insignis (Saussure, 1858) ?

Abstract

The presence of gastropod shells in the environment is crucial for the survival of hermit crabs, and the population's abundance is directly associated with shell availability. Furthermore, understanding the daily activity of the species contributes to elucidating changes in a community's structure. Therefore, the aim of this study was to evaluate the occupation of gastropod shells and the diurnal and nocturnal abundance of Dardanus insignis on the northern coast of the state of São Paulo, Brazil, at eight different depths. Among 527 hermit crabs, 292 were males, 187 were females (35 ovigerous), and 48 were juveniles. The crabs occupied shells belonging to 11 species, with Olivancillaria urceus being the most abundant, followed by Siratus tenuivaricosus and Buccinanops gradatus. The occupation of O. urceus by all demographic groups indicates its high availability in the region and is an important factor that reduces intraspecific competition within the population for this resource. The increased abundance of hermit crabs captured during the nighttime can be attributed to their predominantly nocturnal activity. Additionally, there was an observed concentration of the population at greater depths, where a higher diversity of shell species is available for occupation.