Original paper

Impacts of suspension feeders on the modification and transport of stream seston

Wotton, Roger S.; Warren, Luke L.

Abstract

Suspension feeders collect, and ingest, small particles and egest much larger faecal pellets into which many small particles become bound. Pellets sink through the water column and, if sinking is rapid, they become incorporated into sediments close to where they were produced. If sinking is slower, pellets are carried downstream for much longer distances. As fall velocity (the rate at which a particle settles through a quiescent water column) gives a good indication of downstream particle transport, we used laboratory experiments to investigate the effect of two factors on the fall velocity of pellets egested by blackfly larvae (Diptera: Simuliidae): their composition and their age. Larvae were fed a range of diets (organic only, organic dominated, natural, mineral dominated, and mineral only) and the fall velocity of pellets recorded for larvae of a range of sizes. Fall velocities increased with increasing mineral content, pellets generated from natural stream water during summer conditions being intermediate between the fall velocities of pellets produced by larvae feeding on the organic and mineral diets. Ageing natural pellets for 0, 10, 17, 27, 31 and 41 days resulted a progressive lowering of fall velocity for pellets of a given size. Larger pellets sank more rapidly than small pellets in all experimental treatments.

Keywords

suspension feedersfaecal pelletsfall velocityorganic and mineral content of pelletsageing and conditioning of pelletschalk streams