Macroinvertebrate community changes at coarse sediment recruitment points along two gravel bed rivers

Abstract

Field data from two gravel bed rivers are used to investigate the response of mainstream macroinvertebrate communities to changes in bed sediment character at sites of significant coarse sediment recruitment. There is clear evidence that these points, where downstream fining trends are punctuated, are associated with significant changes in community composition. Community differences are greater between pairs of riffles that straddle recruitment points than between similarly spaced riffles that do not. Taxa that prefer coarse substrate and energetic flows tend to be more abundant below recruitment points where there is also a tendency for taxa diversity to increase. Classification procedures discriminate faunal assemblages at those sites which occur immediately downstream of recruitment points from assemblages at other sites. Although most of the lateral sediment sources examined are tributaries, a number of arguments suggest that, at least in this case, faunal changes are primarily due to abrupt changes in bed sediment character and are not due to concomitant changes in water quality or quantity. Our results suggest that at moderate spatial scales, patterns of coarse sediment recruitment are partly responsible for the spatial organization of macroinvertebrate communities in gravel bed rivers. © 2001 American Geophysical Union