Food-web manipulation in a small, eutrophic Lake Wirbel, Poland: The effect of replacement of key predators on epiphytic fauna

The effect of fish removal on the invertebrate fauna associated with Stratiotes aloides was studied in a shallow, eutrophic lake. The biomass of invertebrate predators was approximately 2.5 times higher in the invertebrate-dominated year (1992) than in the fish-dominated year (1991), while the density of non-predatory invertebrates in 1991 was ca half that in the invertebrate-dominated year. The decrease was due to a sharp fall in the density of epiphytic chironomids, with the density of plant-mining chironomids being far less affected. Marked declines in the density of non-predatory invertebrates in the invertebrate-dominated year were most probably caused by invertebrate predators. Once freed from suppression induced by fish, invertebrate predators were able to control the density of epiphytic prey more effectively than fish.