Fun with Science Club®


			Crab mothers know just what their babies need. Beth Tyler 05.25.01 In April, female Jamaican bromeliad crabs, Metopaulias depressus, lay their larvae in leaf axils, the corner where the leaf meets the branch of a tree or bush, in bromeliad plants (plants in the family Bromeliaceae. There is a pool of water in the leaf axil where the larvae live. After two weeks, the larvae develop into baby crabs. The baby crabs stay in the water for two more months. During this entire time, the mother feeds and takes care of her babies. The water in the leaf axils does not have very much calcium, a nutrient the growing crabs need. Because of this, mothers collect snail shells, which are made from calcium, and put them in the water with their babies. A German scientist wanted to know if mothers knew how many snail shells, or calcium, their babies needed. To find out, he went into the field in April and looked for the little crab nurseries, with larvae and baby crabs, in the leaf axils of bromeliad plants. He did this for two years, finding 12 crab nurseries the first year and 10 the next. In half of the crab nurseries he found, he took out the water and added water with no calcium. He predicted that mothers would know that the water had less calcium and would therefore put more calcium-rich snail shells into it. As he predicted, mothers brought their babies more snail shells when the water had less calcium. Somehow the mothers can sense the amount of calcium in the water, and then adjust the number of snail shells they put into it.


			Diesel, Rudolf. 1997. Maternal control of calcium concentration in the larval nursery of the bromeliad crab, Metopaulia depressus (Grapsidae). Proceedings of the Royal Society of London Series B 264:1403-1406.