An Emerging Decline: Large Consumers Decrease Aquatic Insect Emergence By an Order of Magnitude in a Missouri River Backwater

As local fish diversity is on the rise in some regions, due to non-native species introductions, it is important to understand how fish communities affect links between aquatic and terrestrial habitats. We tested the hypothesis that large consumers (mostly fish, including invasive Asian Carp) alter algae, benthic insects, and emerging aquatic insects. Experiments were conducted in a Missouri River backwater near Wynot, NE using large enclosures that contained a small number of juvenile fish but excluded all adult fish. Preliminary results indicate that average insect emergence increased by as much as a factor of nine following the exclusion of large consumers. Twenty five days after enclosures were deployed macrophyte biomass was also significantly higher within enclosures than in the ambient backwater, where it was essentially absent. Although small fishes within the enclosures consumed some insects, a greater degree of macrophyte reduction and insect suppression occurred within the species rich backwater. Our results suggest large consumers, namely invasive Asian Carp, are drastically reducing algal densities and severing aquatic-terrestrial insect flux through a combination of indirect herbivory and direct predation, ultimately reducing spider presence.