Metal Toxicity Can Affect Dragonfly Nymphs and Ostracods Predation Rates and Food Selectivity: Ecological Implications on Food Webs

Predation is known to play a prominent role in maintaining ecosystem structure and functioning. Despite metals being known to potentially affect predation in aquatic ecosystems, few studies have been conducted, so far, with the aim of evaluating this interplay. In the present study, the effects of four metal salts (copper, cadmium, mercury, and manganese) on the feeding rates and food preference of the dragonfly Tramea cophisa and of the ostracod Chlamydotheca sp. were studied by performing laboratory ecotoxicity tests. Food preference was evaluated by offering four prey species to dragonfly nymphs and three to adult large ostracods. In general, the food preference of both predator species after being exposed to metal salts was not altered, compared with controls, but the feeding rate of T. cophisa decreased in comparison with controls, after exposure to each metal salt, except manganese. Contrastingly, predation rates of Chlamydotheca sp. increased after metal salt exposure. This difference in response can be explained by differences in life-history traits of these two organisms. Both species individuals preferred soft-bodied prey (Oligochaeta, Chironomidae) over water-dwelling crustaceans that are likely to be more difficult to prey upon. Tests evaluating the effects of metals and other chemicals on predation behavior may lead to a better understanding of biotic interactions that can be restricted by chemical stress, improving our understanding of possible food web disruptions underlying chemical stress.