Fecal pellets from a dense aggregation of suspension-feeders in a stream: An example of ecosystem engineering

Abstract

Blackfly larvae (Diptera: Simuliidae) are "allogenie ecosystem engineers" that capture fine particulate and dissolved matter from suspension and egest much larger fecal pellets. We investigated the effects of blackfly larvae on organic matter transport at 25 sites along a small stream that flowed 500 m from a lake to the sea. Blackfly density was high upstream (>6 × 105 ind. m-2) and the numbers of fecal pellets in suspension rose markedly downstream from the blackfly aggregation. A total of 1.6 × 109 fecal pellets (biomass 3.2 kg C d-1) were discharged to the sea each day and 8.0 × 108 pellets (biomass 1.6 kg C d-1) were lost from suspension. Sedimenting pellets were available to the benthic microbial and invertebrate communities.