Abstract
We measured biomass and elemental composition (dry mass, W; carbon, hydrogen, nitrogen, CHN) in eggs and larvae of a mangrove crab, Sesarma rectum . The results are compared with previously published data from a closely related species with abbreviated development ( S. curacaoense ). Egg size of S. rectum increased during embryogenesis, while egg biomass, C content (%W), and the C:N ratio decreased. Initial biomass of eggs and larvae in S. rectum was about half of that in S. curacaoense, also showing lower percentage values of C and H and a lower C:N ratio (indicating a lower lipid content). After hatching, however, the zoeae of S. rectum showed higher growth rates than those of S. curacaoense (presumably due to partial utilisation of internal energy reserves in the latter) and a longer period of development to the megalopa (passing though three vs. only two zoeal stages); as a consequence of these differential growth patterns, S. rectum compensated for the initially lower biomass. Interspecific comparison among neotropical Sesarmidae suggests an intermediate degree of dependence on planktonic food sources in S. rectum , which is lower than in estuarine species with small eggs and an extended mode of development (e.g. Armases angustipes ), but higher than in relatives with larger egg biomass and an abbreviated development (e.g. A. miersii, S. curacaoense, S. fossarum, Metopaulias depressus ). This should allow S. rectum larvae to develop partially within the parental mangrove system, but requiring a limited export towards coastal marine waters with planktonic food sources.
Highlights
Grapsoid crabs, in particular those of the familySesarmidae, show a general tendency to invade nonmarine environments such as brackish, freshwater, and terrestrial habitats.This life style requires physiological adaptations in the adult crabs, namely euryhalinity and/or resistance against desiccation, but frequently adaptive traits in the early life-history stages
Inferring from adult ecology, it may be expected that the semiterrestrial crab Sesarma rectum
On February 7, 1996, seven ovigerous females of Sesarma rectum were collected from their typical habitat, deep burrows that the crabs had constructed in almost dry sandy soil at the upper margin of a mangrove swamp near Bertioga (State of São Paulo, Brazil)
Summary
Grapsidae; for recent major changes in the taxonomy of the Grapsoidea, see Schubart et al, 2000, 2002), show a general tendency to invade nonmarine environments such as brackish, freshwater, and terrestrial habitats (for review, see Anger, 2001). This life style requires physiological adaptations in the adult crabs, namely euryhalinity and/or resistance against desiccation, but frequently adaptive traits in the early life-history stages. These allow for at least partial larval independence from planktonic food sources and for development in nonmarine habitats with low or unpredictable plankton production.
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