Upstream Movements of Benthic Invertebrates in a Lake District Stream

Abstract

Benthic invertebrates in lotic systems drift downstream in large numbers (see references in Bishop & Hynes 1969a; Waters 1969), but little is known about compensatory upstream movements. In amphibiotic insects the upstream flight of females may partially compensate for the drift of eggs and larvae (Roos 1957). Muller (1954) proposed the term 'Colonization Cycle' for the whole process of females migrating upstream, oviposition near the source of the stream, and larvae drifting downstream. This hypothesis is applicable to some species of Trichoptera (Roos 1957; Waters 1968; Elliott 1969), but imagines of most species fly in the same direction as the wind and show no persistent upstream movement (Elliott 1967; Bishop & Hynes 1969a). An alternative mechanism is the upstream movement of benthic invertebrates, and this is the only possible mechanism for species which are aquatic throughout their lives. Upstream movements have been recorded for gammarid amphipods (Macan & Mackereth 1957; Minckley 1964; Muller 1966; Kureck 1967; Lehmann 1967; Hultin 1968), crayfish (Momot 1966), stonefly nymphs (Stehr & Branson 1938), and mayfly nymphs (Traver 1925; Neave 1930; Harker 1953; Macan 1957; Leonard & Leonard 1962). Ball, Wojtalik & Hooper (1963) studied the upstream dispersion of radiophosphorus in a Michigan stream and concluded that the radiophosphorus was probably carried upstream by benthic invertebrates. These upstream movements were quantitatively unknown and were not related to downstream drift. Recent studies in a Canadian river (Bishop & Hynes 1969b) and in a Swedish stream (Hultin, Svensson & Ulfstrand 1969) have shown that substantial numbers of invertebrates move upstream. The purpose of the present study was to investigate the upstream movements of benthic invertebrates in a stony stream. This work is part of a general study of invertebrate drift and benthos in the Wilfin Beck, a small stony stream in the English Lake District.