Population structure of the stone crab Xantho poressa (Olivi, 1792) in a human-restricted access area

Abstract

Some of the elements in the rocky intertidal zone, such as boulders, act as a refuge, mating, feeding and nursery area for marine fauna. In the present study, we analysed the population structure of the intertidal stone crab Xantho poressa in a human-restricted area, between March 2019 and February 2020, comprised of a rocky shore along the SW Atlantic Spanish coast. The study aims to provide information about the size distribution and identify which environmental factors shape the distribution, sex ratio and mating system of the species. The males were significantly larger than the females and no significant difference in size was observed between ovigerous and non-ovigerous females. The sex ratio was biased towards females. Groups constituted by one large male and several females were observed coexisting under a boulder. Other groups of two or more males and various females were also observed during the study. The distribution of the species is mainly determined by the size and weight of the boulder. The complexity of the study area, and the key role of boulders in the distribution of the species, suggests that X. poressa might have a refuge–defence polygynous mating system.