Assessment of the impacts of human trampling on locally endangered crab behavior and its implications for coastal ecosystem conservation

Coastal ecosystems, including tidal flats, are exposed to recreational activity-driven trampling. The white-clawed fiddler crab, Austruca lactea, is endangered in South Korea majorly due to reclamation but recreational trampling also emerged as a potential threat. To assess short-term behavioral responses of individual A. lactea to a single trampling and the long-term population changes under cumulative trampling, we conducted two field experiments for three semilunar tidal cycles. First, we compared the behaviors of two crab individuals, one of whose burrow openings had undergone a single trampling event. Results revealed that trampling delayed the initiation of surface activity, reduced travel distance, and altered the behaviors of the crabs from courting or feeding to vigilance and burrow repair. Second, we constantly exerted trampling on subsets of the crab population for two trampling periods (four and two weeks) and monitored the restoration of their collective behaviors for an additional two weeks. Daily trampling decreased the number of crabs active on the surface and the degree of male courtship indicators, and the rhythms collapsed. After trampling cessation, only courtship indicators recovered after longer trampling treatment. These results imply that continuous coastal visitation without any regulation might aggravate A. lactea population decline in heavily used habitats. Because A. lactea is an indicator species for coastal ecosystem health, we suggest conservation of the habitat area of these crabs based on their behavioral changes caused by human trampling. Our study underscores the importance of assessing the behavioral ecology of benthic animals for tidal flat ecosystem monitoring and conservation areas establishment.