The amount and distribution of calcium in the exoskeleton of intermoult crayfish of the genera Engaeus and Geocharax

Abstract

Total calcium concentration and calcium distribution have been studied in the exoskeletons of the crayfish Engaeus fossor, E. leptorhynchus, Engaeus sp, and Geocharax falcata. In all species the total exoskeleton calcium concentration is low in comparison with most other crustaceans, especially the decapod Crustacea. Furthermore the results suggest that the total exoskeletal calcium concentrations of two of the species (E. fossor and Engaeus sp.) decreases with increased crayfish size whilst one other species studied (G. falcata) maintains a constant concentration of calcium with increased crayfish size. It is suggested that reduction in (relative) calcification is an adaptation to the low calcium concentrations in the waters inhabited by the crayfish. The distribution of exoskeletal calcium in the crayfish species studied was dissimilar. The significance of these differences in calcium distribution is discussed in relation to the habitat requirements of each species.