Larval release and associated tree-climbing behavior of the land hermit crab Coenobita violascens Heller, 1862 (Anomura: Coenobitidae)

Larval releasing behavior of Coenobita violascens Heller, 1862 was studied on a mangrove forest on the banks of a river on Iriomote Island, Japan (24°25′N, 123°46′E) between May and October 2012 and July and September 2014. Larval release was observed on the mangrove root systems, boulders, and fallen trees on the riverbanks. Behaviors from tree climbing to larval release began during nighttime at low tide when ovigerous females approached mangrove trees on the intertidal shore and climbed trees to heights of 0.2-1.6 m. After climbing, they rested on the trunk under the leaf canopy or under the root system to avoid direct sunlight during the day and descended to the roots near the water line following the nighttime high tide. Females immersed themselves fully or partially in river water and released the hatching zoea larvae. Larval release was observed for several days before and after the new moon between July and October and occurred only after sunset; larval release coincided well with high tide. For this species, which is adapted to mangrove habitats, larval release on mangrove roots with tree climbing and clear lunar and tidal rhythms enhances the probability of as many larvae as possible reaching the sea with a receding tide.