title: Competition impedes the recovery of Daphnia magna from repeated insecticide pulses.
abstract: The effects of multiple insecticide pulses on non-target organisms have rarely been investigated in combination with relevant biotic interactions, such as competition. In this study, we examined the effects of two repeated pulses of the insecticide pirimicarb (3, 10, 24 μg/L) on populations of Daphnia magna with or without competition. To investigate the influence of competition, half of the test systems were supplemented with the pirimicarb-insensitive species Culex pipiens. The pesticide pulses were followed by a recovery period of 28 days, which corresponded to approximately three generation times for D. magna. The one-species setup with the Daphnia populations and the two-species setup with both the Daphnia and Culex populations had a precontamination period of 30 days so that intra- and interspecific competitions were present prior to the insecticide pulse. Short-term effects on the survival of the Daphnia population were observed in both setups immediately after each insecticide pulse at the highest concentration level. In the one-species setup, the short-term effects on population survival were increased by intraspecific competition. However, the Daphnia populations in the one-species setup recovered and reached the control level within approximately two weeks after each insecticide pulse. In contrast, in the two-species setup at the highest concentration, we observed culmination of insecticide effects: the Daphnia populations did not recover and their abundance was below the control level until the end of the observation time. Their recovery was impeded by the presence of the competing species C. pipiens for at least four weeks. At low concentrations, no culmination of effects was observed. We conclude that repeated toxicant pulses on populations that are challenged with interspecific competition may result in a multigenerational culmination of toxicant effects.
authors.affiliation: Department of System Ecotoxicology, Helmholtz Centre for Environmental Research (UFZ), Permoserstrasse 15, 04318 Leipzig, Germany. Electronic address: ida.dolciotti@ufz.de.
authors.forename: Ida
authors.initials: I
authors.lastname: Dolciotti
authors.affiliation: Department of System Ecotoxicology, Helmholtz Centre for Environmental Research (UFZ), Permoserstrasse 15, 04318 Leipzig, Germany.
authors.forename: Kaarina
authors.initials: K
authors.lastname: Foit
authors.affiliation: Department of Geography and Environmental Research, Leipzig University, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Herkelrath
authors.affiliation: Department of System Ecotoxicology, Helmholtz Centre for Environmental Research (UFZ), Permoserstrasse 15, 04318 Leipzig, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Liess
mesh_terms: D000818:Animals; D003163:Competitive Behavior / Q000502:physiology*; D003621:Daphnia / Q000187:drug effects* / Q000502:physiology*; D013995:Time; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D014874:Water Pollutants, Chemical
keywords: Competition; Daphnia magna; Multispecies test systems; Repeated exposure