Ecotoxicology and ecophysiology of mysids, with special reference to copper toxicity in Praunus flexuosus

Abstract

Toxicity of dissolved copper was examined in a common coastal mysid population {Praunusflexuosus}. The life cycle and ecophysiology were studied under natural conditions throughout the year, and responses to dissolved copper were determined in the laboratory. Pronounced and ontogenic seasonal differences in copper toxicity for the mysid Praunusflexuosus were observed. Sublethal and lethal parameters (mortality, behaviour, metabolism, reproduction, and bioaccumulation) showed seasonal variation in response to copper toxicity, being highest toxicity in summer. Changes in the form of dissolved copper were measured during toxicity testing, using the chelating resin method to provide a measurement of total and labile (Chelex-available) dissolved copper in the natural seawater used in the toxicity tests. Labile dissolved copper did not show significant variations in the test seawater, confirming that organisms were exposed to constant labile copper concentrations during the toxicity test. The total dissolved copper concentration was significantly higher than the labile form, as organic complexation occurred in natural seawater and during toxicity tests. The labile fraction could be less than 50% of the total fraction. The total dissolved copper concentration decreased significantly when the organism was under stress. While the mortality of the population was insignificant after 10 days of copper exposure (0, 5,25, 75 and 200µg 1^-1) in winter, lethal effects occurred at every copper exposure level after 24 hours (96h LC₅₀ =30.8 µg 1^-1) in summer. The effects of copper on metabolism (respiration and excretion) were very sensitive indicators of sublethal toxicity, which resulted in lethal effects with a prolonged time of exposure. Metabolism shifted to a greater reliance on protein catabolism under copper exposure in both seasons, demonstrating a stronger effect in summer. Total copper content accumulated in the organism increased with increasing copper concentration in solution. Copper accumulation rate was higher in summer. than in winter, increasing to rates of 7.9µg g^-1 dry weight day per day. Reproductive processes were severely disrupted at any copper treatment. Production of juveniles was reduced to zero, because of the high abortion rate, reduction on brood survival and damage to fertilisation processes.

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