Movements of Invertebrates between Stream Channels and Forested Floodplains

Abstract

The magnitude, direction, and temporal aspects of invertebrate movements between two headwater stream channels and their hardwood forest floodplains were determined over one year. There was a net output of numbers of individuals from the floodplains to the channels, whereas there was a net input of biomass to the floodplains. The effect of these movements on the trophic functioning of the floodplains probably was minimal because net numbers exported amounted to <1% of the annual mean density of floodplain invertebrates and the net biomass imported was <4% of the annual mean biomass and <1% of the annual invertebrate production of the floodplains. Invertebrate movements occurred through both drift and crawling. Drift accounted for the majority of individuals moving to the floodplain, but most of the biomass moved onto the floodplains by crawling across the channel-floodplain boundary. Most individuals moved between the channels and floodplains during February-April, the numbers drifting being positively correlated with discharge, whereas movement by crawling was primarily keyed to habitat shifts associated with life history events of species of Ephemeroptera, Trichoptera, and Megaloptera.