Drift

Abstract

Stream-dwelling organisms often are transported downstream in the water column in substantial numbers. Because they have limited swimming ability and apparently are being swept downstream, the phenomenon has been called ‘drift’. While most descriptions of drift focus on invertebrates, downstream transport also has been reported for taxa of the periphyton and some larval fishes and amphibians. Brown and Armstrong (1985) found that 18 of some 60 fish species in an Arkansas river exhibited larval drift. Diatoms also occur in the drift (Müller-Haeckel, 1971), providing nourishment to suspension-feeding invertebrates and resulting in rapid colonization of new habitats and artificial substrates. In this chapter however, and in most of the literature, the principal focus is on insects and crustaceans.