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4522984 
Journal Article 
Reduced grazing rates in Daphnia pulex caused by contaminants: Implications for trophic cascades 
Bengtsson, G; Hansson, LA; Montenegro, K 
2004 
Yes 
Environmental Toxicology and Chemistry
ISSN: 0730-7268
EISSN: 1552-8618 
23 
11 (Nov 2004) 
2641-2648 
Ecotoxicological endpoints based on behavioral traits (e.g., predator avoidance, feeding, and locomotion) may be more sensitive and give more insights into patterns of sublethal toxicity than survivorship tests. In this study, the density-dependent grazing rate of Daphnia pulex pre-exposed to p,p'-dichlorodiphenyldichloroethylene (DDE) (insecticide metabolite) and glyphosate (herbicide), via water or a vector, Scenedesmus spp., was assayed in laboratory experiments. The phytoplankton biomass was estimated from the chlorophyll content, and the pesticide uptake and turnover pattern in Daphnia and Scenedesmus were determined from parallel experiments with a radiolabeled source. Scenedesmus spp. relative net growth rate was inversely and linearly related to the density of the grazer. Daphnia pulex exhibited significant reductions in grazing rate: 30% for those pre-exposed to p,p'-DDE via water and 40% for D. pulex pre-exposed to glyphosate via Scenedesmus spp. Through the process of trophic cascading, this impaired grazing allowed Scenedesmus spp. to grow at higher rates, 70 and 60%, respectively. The reduced grazing efficiencies were associated with the treatments that gave the highest body burden of p,p'-DDE (70 mu g/g dry wt) and the lowest of glyphosate (13 mg/g dry wt). The pattern of results suggests a toxic effect of p,p'-DDE on D. pulex and a growth enhancement of Scenedesmus spp. in response to nitrogen and phosphorus in glyphosate excreted by D. pulex. 
Chlorophylls; Grazing; DDE; Protective behaviour; Phytoplankton; Herbicides; Metabolites; Trophic relationships; Toxicity tests; Chlorinated hydrocarbons; Self purification; Fresh water; Insecticides; Trophic structure; Bioaccumulation; Feeding behaviour; Locomotion; Sublethal effects; Freshwater crustaceans; Pesticides; Uptake; Phosphorus compounds; Growth rate; Feeding; Chlorophyll; Phosphorus; Survival; Vectors; Avoidance behavior; Predators; Toxicity; Biomass; Contaminants; Feeding behavior; Pollution indicators; Glyphosate; Nitrogen; Scenedesmus; Density; Laboratories; Daphnia; Growth Rates; Pollutants; Water Pollution Effects; Absorption; Daphnia pulex; Cladocera