Settlement behavior and substrate Preference of the coconut crab Birgus latro megalopae on natural substrata in the laboratory

Although they are land dwellers, coconut crabs, Birgus latro, spend planktonic larval development in the sea and immigrate to the land as megalopae carrying gastropod shells. Better knowledge of settlement behavior and habitat requirements during the early life stages can assist in conservation of depleted coconut crab populations. Our objectives were to evaluate settlement behavior of coconut crab megalopae from 0 to 6 d post-metamorphosis (dpm), and determine the substrate preference (open sand, coral fragments, or brown algae) of 0-12 dpm megalopae. Early megalopae (0-3 dpm) were active swimmers during the night. The walking activity of naked megalopae was directly correlated with shell-inspection behavior during the day, peaking at 2-3 dpm. Almost all megalopae wore shells by 5 dpm and the walking activity of megalopae wearing shells was higher during the night than the day. Based on our observations, we hypothesize that megalopae migrate to the coast by nocturnal flood-tide transport and emigrate from the sea during the nocturnal full tidal phase to minimize predation risk. In the substrate choice experiment, early megalopae exhibited no preference for any substrata, and shell-less megalopae experienced the highest mortality, probably because of cannibalism. The survival rate plateaued at 9 dpm associated with an increase in the proportion of individuals wearing shells and of the onset of active habitat selection for complex substrata (coral fragments or brown algae). This suggests that shells and structural complex habitats are important for survival during the initial benthic phase of the coconut crab. (C) 2015 Elsevier B.V. All rights reserved.