Population biology of the endangered land crab Johngarthia lagostoma (H. Milne Edwards, 1837) in the Trindade Island, Brazil: Identifying crucial areas for future conservation strategies

The life history of insular gecarcinid crabs is divided into a marine larval and an adult phase, adapted to the terrestrial environment. As adults, individuals migrate seasonally to locations near the sea, engaging in reproductive behaviors. Therefore, identifying breeding and recruitment areas is crucial for the conservation of insular gecarcinids, especially for those endangered, such as Johngarthia lagostoma (H. Milne Edwards, 1837). We used sex ratio and sexual dimorphism analyses (body and cheliped size) as well as records of juveniles and adults to describe the population structure of J. lagostoma in the Trindade Island, Brazil. During the reproductive period, several population parameters were compared among sites with different altitudes, comprising two beaches (Andradas and Tartarugas) and two hills (Príncipe, 136 m; and Desejado, 612 m). Overall, males predominated in the population and invested more in body and cheliped growth than females. However, at Andradas Beach, it was observed a similar frequency of adult males and females as well as a small difference in the body size between the sexes. In comparison, the smallest crabs were found at Príncipe Hill. The analyzed population presented a predominance of adults, especially at Andradas Beach (93.1%). Compared to the other sites sampled, Príncipe Hill showed the highest abundance of juveniles (males: 22.2%; females: 40.8%). Thus, Andradas Beach was considered a reproductive site, while Príncipe Hill had the highest density of juveniles, which makes them priority areas for the conservation of J. lagostoma in Trindade Island.