DEVELOPMENT OF CULTURE AND TOXICITY TESTING METHODS FOR THE FRESHWATER COPEPOD BRYOCAMPTUS ZSCHOKKEI
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The aim of this thesis was to evaluate the use of a meiofaunal copepod as a test species for assessing the developmental and reproductive effects of toxicants relevant to freshwater ecosystems. The harpacticoid copepod Bryocamptus zschokkei was chosen as a candidate test species as it possesses several attributes (widespread distribution, small size and fast development times) that are considered pre-requisites for toxicity test organisms, and has previously been shown to be a sensitive component of the stream community to contaminant exposure. Prior to conducting toxicity tests with B. zschokkei, studies were performed to evaluate the effects of water hardness and food quality on the development and reproduction of this copepod. These data were then used to define optimal culture conditions. Bryocamptus zschokkei was insensitive to water hardness at <150 mg 1ˉ¹ (as CaCO3), reflecting its range of tolerance in the field and suggesting the potential for toxicity testing across a range of hardness levels. Food quality affected development and reproduction: beech leaves (Fagus sylvatica L.), conditioned for 2 weeks supported optimal overall development to adult and reproduction of B. zschokkei and were chosen for use in subsequent culturing and testing regimes. Development and reproduction assays for assessing the effects of environmental parameters on B. zschokkei were combined to produce the first full life-cycle toxicity test for a freshwater copepod. This life-cycle test was relatively quick (6 weeks at 20°C) and is highly reproducible. The effects of three reference chemicals, the trace metal zinc, the pesticide lindane, and the moulting hormone 20-hydroxyecdysone (20-HE), were measured using this toxicity test. There was no effect of 20-HE (0-269 µg 1ˉ¹) on the life cycle of B, zschokkei. Bryocamptus zschokkei was, however, relatively sensitive to zinc and lindane compared with other freshwater crustaceans although sensitivity depended on the chemical and the duration of exposure. A model of ‘equiproportional development' was used to aid interpretation of the mechanism of toxicity of lindane, which was found to act by significantly prolonging the development time to adult. Reproductive endpoints (numbers of eggs and nauplii per female) were the most sensitive measure of zinc and lindane exposure, with lowest observed effect concentrations (LOEC) of 0.48 mg Zn 1ˉ¹ and 32 fig lindane 1ˉ¹, respectively. An increase in abortion frequency, observed for these contaminants, may have potential as a biomarker of stress for this copepod. In conclusion, it is proposed that toxicity tests with B. zschokkei should be included in contaminant assessment procedures for freshwater systems as they would increase the choice and ecological relevance of current testing regimes.
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