Larval release rhythm of the land hermit crab Coenobita cavipes Stimpson, 1858 (Anomura, Coenobitidae) on Iriomote Island, Japan

The larval release behaviour of Coenobita cavipes Stimpson, 1858 was studied on Iriomote Island, Japan between June and September 2012. The larval release was observed for several days before and after the new and full moons between July and August and showed semi-lunar rhythms. The larval release occurred 1-3 h after sunset and the peak time was almost 30 min earlier in August than in July. The time was not synchronised with nocturnal high tides in earlier and later days in each phase of syzygy. Emerging from residual lowland forests behind the coast, ovigerous females walked towards the river's water edge and released larvae at the swash zone on the riverbank in the lower river. Therefore, they do not need to synchronise the larval release to coincide with the timing of high tide, unlike their congeneric nearest neighbour, C. violascens Heller, 1862, which releases larvae on the mangrove roots in the upper river.