Effect of acute acidic stress on survival and metabolic activity of zooplankton from Lake Biwa, Japan

ABSTRACT Acute acidic stress from sources such as acid rain might impact lake ecosystems in many aspects. Because zooplankton are sensitive to environmental change, they could be a good biotic indicator of acidification effects. We investigated survival and metabolic rates of 3 dominant zooplankton taxa in Lake Biwa, the cladoceran Daphnia pulicaria and the copepods Eodiaptomus japonicus and Cyclopoida spp., when subjected to different pH values (pH 4.0–8.0) at low (10 °C) and high (20 °C) temperatures. Because mortality of D. pulicaria and Cyclopoida spp. exceeded 50% over 24 h of incubation at pH < 4.6, but for E. japonicus at pH < 5.6, E. japonicus may be more vulnerable to acidic stress than the other 2 taxa. This vulnerability to acidification slightly increased at 10 °C for each taxon. Metabolic rates in D. pulicaria remained relatively constant over a wide pH range (4.6–8.0), but those of both copepods decreased at acidic conditions (pH 4.6–7.0). This decrease of metabolic rate might be related to their swimming activity, which decreased in acidic conditions.