Comparison of fecundity, embryo loss and fatty acid composition of mangrove crab species in sewage contaminated and pristine mangrove habitats in Mozambique

The effects of anthropogenic activities combined with the lack of technical solutions for sewage treatment have lead to serious contamination problems in the coastal ecosystems of East Africa. However, not all contaminants can be considered pollutants. Determining when contamination results in pollution requires not only chemical but also biological measurements. Because benthos integrates conditions over time, macrobenthic organisms are considered good bioindicators to assess local environmental quality. Crabs constitute one of the most important macrofauna taxa in terms of abundance, species richness and biomass in mangrove ecosystems. In the present study, the reproductive potential and quality of Uca annulipes population inhabiting a peri-urban mangrove, subjected to domestic sewage discharges, was compared to populations inhabiting pristine mangroves. Fecundity, egg quality (fatty acids composition) and potential fertility were evaluated and compared by sampling a representative fraction of ovigerous females captured in each of the mangrove habitats at two, seasons (February to March, 2006 - wet season; and August to September, 2006 - dry season). Most of the measured reproductive parameters of U. annulipes were different at Maputo peri-urban mangrove when compared to nearby pristine locations. Although we cannot prove that sewage discharge done at Costa do Sol mangrove was the main factor influencing the reproductive dynamics of U. annulipes populations, at this peri-urban mangrove this fiddler crab species extended its reproductive season, increased fecundity, as well as improved embryo quality, mainly regarding the concentration of SFA and MUFA, in relation to the pristine mangrove populations.