Seasonal variations of the effect of temperature on lethal and sublethal toxicities of ammonia for three common freshwater shredders.

In a context of global change, increases in temperature and in ammonia concentration should strongly affect the crustaceans of wetlands. We experimentally examined, at three different seasons (i.e. winter, spring, and summer), the effect of temperature (12, 18, and 24°C) on the lethal (survival rates) and sublethal (oxygen consumption) toxicity of unionized ammonia (NH(3)) on the amphipods Gammarus pulex and Gammarus roeselii and the isopod Asellus aquaticus. Our results demonstrate (1) a gradient of increasing tolerance and survival from G. roeselii to G. pulex and A. aquaticus, (2) an increasing toxicity of ammonia with temperature, and (3) a strong seasonal variation of the tolerance to ammonia, with a higher tolerance of individuals in winter than in summer. However, the sub-lethal effect of ammonia on the oxygen consumption rate was species dependant and changed according to temperature or season. Global change and resulting variations in crustacean densities will potentially affect the ecosystem functioning (e.g. organic matter recycling).