The macroinvertebrate faunas of riffles and pools

Macroinvertebrate data from studies of rivers, principally in upland areas, of North America (9) and U.K. (8) were examined to identify differences in the faunas of riffles and pools. Overall the number and representation of taxa in the two habitats was similar although some organisms (e.g. Simulium, riffles; Corixa, pools) may characterise each habitat. Significantly higher mean total densities were detected in riffles compared to pools and this confirmed the general conclusions from a number of individual studies: significantly higher densities in pools were never reported. The relative abundance of major groups (Orders) in each habitat was variable: in general, Ephemeroptera formed a higher proportion of the total density in riffles than pools and the reverse was found for Diptera. Only the Ephemeroptera showed significant differences in density between the two habitats, riffles supporting higher densities than pools. Considering families, only Baetidae and Simuliidae showed significant differences in density, riffle density being greater than pool density. Community analyses, commonly used in biological surveillance, indicated that it is unlikely that major misclassification of sites will result from the use of data collected from one habitat (riffle/pool) only. Further studies are required at lowland sites to test the general applicability of the conclusions.