Seasonal and interpopulational variability in fecundity, egg size, and elemental composition (CHN) of eggs and larvae in a grapsoid crab, Chasmagnathus granulatus

Reproductive traits at the beginning and the end of the annual reproductive season were compared between two populations of the intertidal crab Chasmagnathus granulatus living in ecologically contrasting habitats: (1) Mar Chiquita (MC) (37 degrees 45'S, 57 degrees 19'W), a highly productive estuarine coastal lagoon with strong salinity fluctuations. (2) San Antonio Bay (SA) (40 degrees 46'S, 64 degrees 50'), a physically stable but less productive coastal marine environment. Number, size, and elemental composition (CHN) of eggs and larvae differed significantly between populations. Regardless of the season, more but smaller eggs and larvae were produced in MC, while eggs and larvae from SA revealed higher dry mass and C/N ratios indicating higher lipid content. A latitudinal temperature gradient cannot explain these patterns, suggesting that other environmental factors including salinity, quality or quantity of benthic food sources and productivity may be responsible. In both populations, fecundity and biomass per egg were higher at the beginning as compared to the end of the reproductive season. As a consequence, the reproductive effort was consistently maximal at the beginning of the season. At MC, also variability was found between two successive years. Intraspecific (both interpopulational and seasonal) variations in reproductive and developmental traits may be important for the formation of physiologically different metapopulations along the wide geographic range of C. granulatus.