ELEMENTAL COMPOSITION (CHN), GROWTH AND EXUVIAL LOSS IN THE LARVAL STAGES OF 2 SEMITERRESTRIAL CRABS, SESARMA-CURACAOENSE AND ARMASES-MIERSII (DECAPODA, GRAPSIDAE)

Larvae of two semiterrestrial crab species from Jamaica (Sesarma curac aoense and Armases miersii) were reared in the laboratory, and changes in dry weight (W), carbon (C), nitrogen (N), and hydrogen (H) were me asured during development from hatching through metamorphosis. In A. m iersii, larval growth was also followed in their natural environment, a supratidal rock pool. Both species show an abbreviated larval develo pment, with only two zoeal stages in S. curacaoense and three in A. mi ersii. Unusually high initial C contents (c. 45% of W), together with a high C:N weight ratio (>5) in zoeae of both species indicate that hi gh amounts of yolk reserves persist from the eggs. The zoeal stages, i n particular those of S. curacaoense, show little growth compared with most marine crab larvae. This suggests that yolk reserves are partial ly utilized as an energy source during early larval development (parti al lecithotrophy), and hence, the availability of external food source s should be less critical here than in planktotrophic marine crab larv ae. A decreasing trend in the C:N ratio suggests that lipids play a ma jor role as an internal energy source in the larval development of bot h species, while the protein fraction increases proportionally during larval growth and morphogenesis. Growth of A. miersii larvae was, on a verage, slower, and the decrease in the C:N ratio faster in a natural rock pool as compared with a laboratory culture. We suggest that growt h in supratidal rock pools may be food-limited. Such conditions should select for an abbreviated type of larval development and an enhanced degree of lecithotrophy, as is found in this species. Production of ex uvial matter (W, C, N, H) was measured in all larval stages and in the first juvenile crab of both A. miersii and S. curacaoense. On average , exuviae of the former are heavier but contain less C (as a percentag e of W) than those of the latter. This indicates a higher content of i norganic materials in the larval exoskeleton of A. miersii than in S. curacaoense. In the zoeal stages I and II of both species, the exuvial losses amount to only <3% of late premoult body C. This is interprete d as an energy saving mechanism, and an adaptation to partially food-i ndependent development. Later stages (increasingly dependent on food) lose larger amounts of biomass with the cast exoskeleton. In summary, both S. curacaoense and A. miersii show ontogenetic traits that can be interpreted as adaptations to food-limited conditions in freshwater a nd terrestrial environments: abbreviated larval development, partial l ecithotrophy, and a low exuvia production during early larval life. Th ese adaptations appear more pronounced in S. curacaoense than in A. mi ersii.