Rapid Assessment of the Sex Ratio of the Fiddler Crab, Uca tangeri, in Two Mangrove Habitats on the Bonny River

A rapid assessment of the sex ratio of the fiddler crab, Uca tangeri, was undertaken in two mangrove habitats on the Bonny River which were undergoing intense human impact as a result of dredging and urbanization activities. The contrasting adult sex ratios of 4:1 of male to female at Eagle Island and 1:2.6 at Rumuolumini and or juveniles showing 2.4:1 (Eagle Island) and 1:1.8 (Rumuolumini) were highly significant (χ2 test, P<0.05). This shows evidence of studies supporting deviation in Uca spp from the 1:1 proportion. Evidence of anthropogenic activity and intensive socioeconomic exploitation provided no explanation for the contrasting high deviation in ratio of males to females between Eagle Island and Rumuolumeni habitats. Megalopae settlement is evident but the physical, chemical and interspecific cues that determine gender balance are necessary for any intended future conservation planning.

The euryhaline crab Uca tangeri showed metabolic differences to sex and environmental salinity

This study constitutes a first attempt to investigate sex differences in osmoregulatory capacity and metabolic responses in relation to hyper- and hypo-osmoregulation in the intertidal euryhaline crab Uca tangeri. Adult male and female specimens from Cadiz Bay, Spain (36°23′–37′N 6°8′–15′W), were acclimated to three different environmental salinities (12, 33 and 55 psu) during 7 days, and several parameters were assessed in haemolymph (osmolality, glucose, amino acids, triglycerides and lactate) as well as in metabolic key organs (hepatopancreas, anterior and posterior gills: glycogen, free glucose, amino acids and triglycerides). Specimens from both sex exhibited high and similar hyper- and hypo-osmoregulatory capacities. However, metabolite levels were differentially affected upon acclimation to low and high salinity in several metabolic organs and haemolymph of male and females: (i) glycogen in gills, (ii) free glucose in gills and hepatopancreas, (iii) amino acids in hepatopancreas, (iv) triglycerides in haemolymph, hepatopancreas and posterior gills, and (v) lactate in haemolymph. The results suggest the occurrence of differential metabolic adjustments upon hyper- and hypo-osmoregulation related to sex in the intertidal euryhaline crab U. tangeri.