Do native land crabs hinder forest regeneration on Socorro Island?

• Low seedling and sapling densities indicate poor tree recruitment. • Adult DBH distribution reflects historical recruitment gaps. • Land crabs act as key recruitment barriers via seed predation. • Low seedling emergence suggests other recruitment barriers (e.g. climate change or genetics) Forests are important ecosystems whose long-term sustainability depends on the recruitment of new individuals. Socorro Island (Revillagigedo Archipelago, Mexico) has endemic forests with a pattern that could indicate poor regeneration. We evaluated the five dominant tree species to determine the state of regeneration of the forests and tested if the land crab Johngarthia oceanica is the main seed predator and, therefore, the main recruitment barrier. We found a lack of current recruitment, since the youngest life categories (seedlings and saplings) showed lower or null densities of individuals, than those in the adult category. In addition, the DBH distribution for the five species, showed that only Guettarda insularis has a higher abundance of saplings than adults, while the rest of the species did not. Crab exclusion experiments showed that crabs ( J. oceanica) mainly consumed two tree species: Psidium socorrense and Sideroxylon socorrense . In the areas where crabs had access, they preyed on 83.7% and 99% of the seeds, respectively. The other two species: G. insularis and Ilex socorroensis , did not show significant differences between control and predator exclusion treatments. Germination of all species only occurred in the crab exclusion zones; however, germination percentages were very low, they ranged between 0.008 % ( G. insularis ) and 5.65 % ( P. socorrense ). Although crabs represent an important recruitment barrier for P. socorrense and S. socorrense , the main regeneration problem that these forests appear to face is the low germination rate, which could be due to environmental or genetic factors.