Effects of geophysical cycles on the rhythm of mass mate searching of a harvested mangrove crab

► The harvested crab Ucides cordatus exhibits cycles of searching for mates en masse. ► The rhythm of mate searching is linked to the syzygy tide inequality cycle. ► Mating shifted between new and full moon depending upon the highest tidal amplitude. ► The rhythm seems to be endogenous, favouring optimal larval release at strongest tides. ► Knowing the link between geophysical cycles and mating can help in placing capture bans.