Effects of pH on electron transport system (ETS) activity and oxygen consumption in Gammarus fossarum, Asellus aquaticus and Niphargus sphagnicolus

1. Electron transport system (ETS) activity and oxygen consumption were measured in three crustacean species (Gammarus fossarum, Asellus aquaticus and Niphargus sphagnicolus) that differ in their pH tolerance. Measurements were made under four different pH regimes: strongly acid (pH 4.5-5.0), weakly acid (5.5-6.0), 'neutral' (7.0-7.8) and alkaline (8.5-9.0). 2. The significantly lower ETS activity/respiration (ETS/R) ratios observed in strongly acid water than in neutral and alkaline water indicate an effect of acidity on metabolism of the organisms. The main reason for the lower ratios is not increased oxygen consumption (except for G. fossarum in strongly acid water) but decreased ETS activity. Metabolic potential was lower in strongly and weakly acid water than in neutral water. Therefore, efficient exploitation of metabolic potential (i.e. of relatively large production of ATP with the existing enzyme machinery) probably enables N. sphagnicolus and A. aquaticus to survive in an acid environment. 3. Increased oxygen consumption of G. fossarum in strongly acid water indicates an acid stress that leads to the collapse of metabolism and, consequent death of the animals. 4. Although N. sphagnicolus is found exclusively in permanently acid water, no negative effect of alkaline water on metabolism was observed. This species can, therefore, be best considered as an acid-resistant species, not an acidobiont.