Is salt the solution? Interactions between trace-metal uptake and salinity in the freshwater crab Potamonautes warreni Calman, 1918 (Decapoda: Brachyura: Potamonautidae).

The article focuses on the uptake of dissolved trace metals zinc (Zn²⁺) and cadmium (Cd²⁺) in the true freshwater crab Potamonautes warreni from South African rivers near mining areas, investigating whether these metals enter via sodium (Na⁺) and calcium (Ca²⁺) ion uptake pathways. Experimental acclimation of P. warreni to varying Na⁺ and Ca²⁺ concentrations showed that Cd²⁺ uptake into haemolymph increased under Na⁺-replete conditions, while whole-body Zn²⁺ uptake was also elevated with higher Na⁺, suggesting physiological changes influence metal uptake. Compared to the catadromous crab Eriocheir sinensis, P. warreni exhibited lower permeability and trace-metal uptake rates, likely reflecting its greater adaptation to freshwater environments. The study concludes that trace-metal uptake in P. warreni involves multiple mechanisms, including paracellular pathways, and that increased environmental salinity or Na⁺ concentration does not necessarily reduce metal absorption, highlighting the importance of species-specific physiological responses in assessing vulnerability to metal contamination.