Beneath the surface: co-habitation of land crabs recruits of Johngarthia lagostoma and its relevance for conservation on oceanic islands

Abstract

Abstract Gecarcinid crabs have their life cycles in antagonistic scenarios, with their larvae developing in the sea and the juvenile/adult phases occurring on land. Adults migrate from land to sea to release their larvae, which return to land upon reaching the megalopa stage. Recruitment and early instar traits in land crabs remain unknown, leading to some species lacking age-specific information. It is expected that recruits exhibit cryptic behavior, potentially occupying conspecific burrows. We evaluated whether recruits of Johngarthia lagostoma (H. Milne Edwards, 1837) on Trindade Island, Brazil, co-inhabit larger conspecific burrows, describing this occurrence, and examining their growth patterns, density, and body size across different lunar phases. Johngarthia lagostoma recruits inhabit conspecific burrows, either abandoned or occupied by adult crabs, but always with leaves stored in the inner chamber. Recruits in co-inhabiting behavior reach a maximum carapace width of 7.3 mm and, after that, they are likely detected by the adults and possibly cannibalized or leave burrows naturally. During the full moon, the higher density and smaller size of recruits were recorded, indicating a recruitment lunar phase. It is crucial to ascertain the prevalence of co-inhabitation behaviors in other land crab species to expand the knowledge about recruitment patterns in these key community species.