Reproduction of the Fiddler Crabs Uca longisignalis and Uca spinicarpa in a Gulf of Mexico Salt Marsh

Monthly field sampling of active animals in a Louisiana coastal salt marsh monitored changes in size class frequency distributions, ovarian development of females, and rates of egg extrusion for two species of Uca endemic to the Gulf of Mexico. Ovigerous females occurred no earlier than February for Uca spinicarpa and April for Uca longisignalis. Peak percentages of ovigerous females were observed in June 1992 for Uca longisignalis (67%) and in March 1993 for Uca spinicarpa (85%). Peaks in ash-free dry weight (AFDW, in g) of females coincide with peak periods of ovarian development and subsequent ovigery. Mean biomass as AFDW of males and females combined for Uca longisignalis was 0.26 g individual-1 and for Uca spinicarpa was 0.17 g individual-1 A significant correlation existed between AFDW and carapace width in both species, males and females. U. longisignalis appears to be of warm-temperate lineage, and its reproductive activity is the more seasonally restricted, with later ovarian development, earliest egg laying delayed to late spring, and peak ovigery in summer. In keeping with putative tropical affinities of Uca spinicarpa, ovarian development is episodic over a longer period from late winter to summer, and eggs are produced earlier in the year. The more striking seasonality in reproductive activity and biomass peaks for Uca longisignalis may also reflect some nutritional dependency on temperate, annual marsh plants that characterize its preferred habitats.