Meeting Abstract
Legally or not, mangroves have been used as biofiltering systems of wastewater (WW) effluents in tropical countries. Although this release enhances the ecosystem functioning (e.g. primary production), previous studies showed that WW discharges impact crab species, which are key ecosystem engineers. The WW impact occurs at different scales ranging from population effects down to individual and cellular damage. One of the major pollutants in WW effluents is ammonia, known to be toxic for many crustaceans. To better understand the effects of WW-released ammonia on mangrove crabs, this study focused on a mangrove forest located on the island of Mayotte (Indian Ocean). This experimental site is used to monitor the ecological and physiological effects of daily WW discharges. In the control area, NH4-N concentration is about 0.11 mgL-1, but for the impacted area, values present a high variability (3.3 to 75 mgL-1). In laboratory condition, the physiological effects of ammonia concentrations up to 80 mgL-1 on the Spider crab (Neosarmatium meinerti) were determined with a focus on osmoregulation, excretion and energy metabolism (animal respiration rates, mitochondrial activity in the gills). NH4-N at 2.5 and 80 mgL-1 induced enzyme activity alterations for the Na+/K+– and H+-ATPase pumps, especially in the anterior gills. However, hemolymph osmotic pressure is maintained constant even if ammonia accumulates at high exposure. Also, respiration rates is increased with ammonia exposure but mitochondrial activity tends to decrease in the anterior gills. These results confirm the negative effects of ammonia on crab physiology. This can at least partially explain the ecological changes observed in the field.
