The trophic cascade from fish to benthic algae: manipulation of habitat heterogeneity and disturbance in experimental flow-through pools

Abstract

To investigate the effects of environmental change on the trophic cascade from fish to benthic algae, two 26-day experiments were conducted in outdoor flow-through pools. Habitat heterogeneity was manipulated by filling grooves under tiles with wood. Disturbance was simulated by removing invertebrates and benthic algae from tiles with a stainless steel brush 10 days before the end of the experiment. Benthic invertebrates and algae rapidly colonized the pools. Japanese dace Tribolodon hakonensis that had been introduced as a top predator fed predominantly on ephemeropteran nymphs, chironomid larvae, trichopteran larvae, and benthic algae. Predation and intimidation by the dace reduced the number of ephemeropteran nymphs and lowered the percentage of invertebrates on the upper surfaces and sides of the tiles. Consequently, dace increased the algal biomass through a trophic cascade. When dace were present, a disturbance did not reduce the numbers of invertebrates at the end of the experiment, probably because most invertebrates recolonized the tiles and new invertebrates rapidly colonized the pools. The manipulation of habitat heterogeneity reduced the number of trichopteran larvae, but did not affect other invertebrates that used all surfaces of the tiles. Consequently, trophic cascades were not damped by these changes of habitat heterogeneity and disturbance.