SENSITIVITY OF THE CRUSTACEANS GAMMARUS-PULEX (L) AND ASELLUS-AQUATICUS (L) TO SHORT-TERM EXPOSURE TO HYPOXIA AND UNIONIZED AMMONIA - OBSERVATIONS AND POSSIBLE MECHANISMS

Episodic organic pollution results in short-term increases in the ammonia concentration and reductions in the dissolved oxygen (DO) concentration of receiving waters. This study provides information on the lethal effects of 24-h pulses of high ammonia and low DO on two common freshwater crustaceans. Both inter and intraspecific differences in sensitivity were observed. Asellus aquaticus was five times more resistant to hypoxia and two times more resistant to unionized ammonia and Gammarus pulex. Moreover, for both stressors, juveniles were less susceptible than adults. Interspecific differences in ventilation rate and blood characteristics (i.e. haemocyanin concentration and oxygen affinity) could explain interspecific differences in susceptibility to hypoxia, and possibly ammonia. Intraspecific differences in ventilation rate may partly explain the reduced susceptibility of juvenile G. pulex to these stressors.