The role of ion regulation in the control of the distribution of Gammarus tigrinus (Sexton) in salt-polluted rivers.

Abstract

Fluctuating salinities at different sites on the German salt-polluted rivers Werra and Weser were compared with extracellular ion levels of specimens of Gammarus tigrinus (Sexton; Amphipoda, Crustacea), collected at the same sites. G. tigrinus regulated haemolymph concentrations of inorganic anions (Cl-, SO(4)2-, PO(4)3-) and cations (Na+, K+, Mg2+, Ca2+) during fluctuations of salt pollution in the upper Weser. This capacity to regulate varying levels of salt pollution in the upper Weser, correlated well with the distribution of the brackish amphipods in this river ecosystem. G. tigrinus tolerated periods of Na+ and Cl- stress (> 380 mmol l-1) without compensating these maxima by regulating extracellular Na+ and Cl-. However, during such bursts of Na+ and Cl- stress in Werra and Weser, the ability to regulate extracellular [K+] at river water K+ stress of > or = 6.0 mmol l-1 may explain why this brackish species has been more successful in these rivers than its competitors like Gammarus pulex. The present investigation demonstrates that the water salinity affects the [NO3-] in the haemolymph of G. tigrinus. With increasing hypo-osmotic stress the animals accumulate increasing amounts of NO3-. A simultaneous increase in stream water [NO3-] causes an additional accumulation of NO3- in the haemolymph. The high extent of accumulation indicates that active ion transport systems may be involved. The accumulation of NO3- in the haemolymph has low physiological consequences to G. tigrinus, but when hypo-osmotically stressed under anoxic conditions, nitrite formed by the reduction of nitrate may have an adverse affect on the metabolism of G. tigrinus.