Concurrent aquatic microcosm and and mesocosm experiments evaluating the ecological impact and fate of the pyrethroid insecticide cyfluthrin were conducted at the University of North Texas Water Research Field Station. Sixteen 1.9 m3 microcosms and fourteen 634.7 m3 mesocosms were established using water, sediments, biological inoculum, and bluegill sunfish (Lepomis machrochirus Rafinesque) from the same sources. Cyfluthrin impacts were not observed on mesocosm bluegill, but a slight decrease in growth was observed in the microcosm bluegill.
Two different types of microcosm controls were established, with and without young-of-the year bluegill. The fishless controls were established to partition the predation impacts of bluegill from the insecticide effects in the microcosms. Bluegill did not strongly impact epibenthic colonizing insects in our system but fed on epiphytic and emerging insects throughout, i.e., Callibaetis, diptera pupae, and odonates. The exuviae collection proved to be a sensitive measure of emergence. Bluegill effects on zooplankton populations in the microcosms were typical in that larger organisms were preferentially selected. Rotifers were numerically dominant in tanks with fish as a result of reduction of larger competitors and invertebrate predators.
Microcosms and mesocosms exhibited very similar trends with regards to insecticide effects on invertebrate population dynamics. The mesocosms and microcosms supported similar zooplankton populations. Microcosms produced fewer total organisms but supported the same sensitive taxa and provided adequate supplies for bluegill growth to occur normally.