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 curacaoense and Armases miersii) were reared in the laboratory, and changes in dry weight (W), carbon (C), nitrogen (N), and hydrogen (H) were measured during development from hatching through metamorphosis. In A. miersii, larval growth was also followed in their natural environment, a supratidal rock pool. Both species show an abbreviated larval development, with only two zoeal stages in S. curacaoense and three in A. miersii. 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 high amounts of yolk reserves persist from the eggs. The zoeal stages, in particular those of S. curacaoense, show little growth compared with most marine crab larvae. This suggests that yolk reserves are partially utilized as an energy source during early larval development (partial lecithotrophy), and hence, the availability of external food sources should be less critical here than in planktotrophic marine crab larvae. A decreasing trend in the C:N ratio suggests that lipids play a major role as an internal energy source in the larval development of both species, while the protein fraction increases proportionally during larval growth and morphogenesis. Growth of A. miersii larvae was, on average, slower, and the decrease in the C:N ratio faster in a natural rock pool as compared with a laboratory culture. We suggest that growth 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 exuvial 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 percentage of W) than those of the latter. This indicates a higher content of inorganic 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 interpreted as an energy saving mechanism, and an adaptation to partially food-independent 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 and terrestrial environments: abbreviated larval development, partial lecithotrophy, and a low exuvia production during early larval life. These adaptations appear more pronounced in S. curacaoense than in A. miersii.