Managing the offspring environment: brood care in the bromeliad crab, Metopaulias depressus

Summary

Maternal modification of the larval environment was studied in the bromeliad crab, Metopaulias depressus (Decapoda, Grapsidae). The bromeliad crab breeds in rain water stored in the leaf axils of large Jamaican bromeliads. The physico-chemical water conditions are highly unfavorable for the development of the larvae. Water in nursery axils contained no leaf litter and up to 14 empty snail shells, whereas other axils were partly or completely covered with leaf litter and rarely held snail shells. Mother crabs removed leaf litter from nursery axils, and occasionally from neighboring axils. Nursery axils contained twice as much dissolved oxygen (DO₂) at night when DO₂ is at a minimum, and less dissolved carbon dioxide (DCO₂) than axils unattended by a crab. The higher DO₂ content in nurseries meets the respiratory needs of an average sized brood, but the lower concentration in axils with litter may not. It is suggested that the higher DO₂ and lower DCO₂ concentrations in the nursery axils result from a water circulation produced by the mother and her leaf litter cleaning behavior. The low pH and the Ca²⁺ content in the water of unattended bromeliad axils are unfavorable for development of larvae and young. Mother crabs significantly increased pH and Ca²⁺ by adding empty snail shells to the nursery-axil water. In experiments where the brood was transferred to other axils, mothers switched from the nursery axil to the new axil containing the brood, and there continued caring for their offspring.