The Role of Drift Dispersal in Production Ecology of a Stream Mayfly

The role of drift behavior in the production ecology of the mayfly Tricorythodes atratus McDunnough was investigated in a headwater reach of the Mississippi River in northern Minnesota, USA. Comparison of drift and bottom samples revealed that larger nymphs exhibited a greater propensity to drift; in bottom samples, small immatures (1—2 mm) were predominant in a study riffle, whereas larger nymphs (>2 mm) were relatively more abundant in a downstream pool. Annual production was 8.56 g.m — 2 .yr — 1 (dry mass) and the annual turnover ratio (annual production/annual mean biomass) was 26; the species was bivoltine. Errors in production rate estimation resulting from sampling a single habitat were substantial when differential size dispersal of nymphs occurred.