SAND EROSION BY MOBILE PREDACEOUS STREAM INSECTS - IMPLICATIONS FOR ECOLOGY AND HYDROLOGY

Despite increasing knowledge of the ability of keystone animal species (''ecosystem engineers'') to change their physical environment, there is little and inconsistent evidence that benthic invertebrates affect the erosion of bottom material in streams. Therefore we designed fiel d stream experiments and observations to investigate the effect of mob ile predaceous stonefly (Dinocras cephalotes) larvae on sand erosion. When short of prey, the stoneflies erode sand from stream riffles ther eby deepening the interstices between cobbles. On the basis of reasona ble assumptions, we speculate that Dinocras has an erosion potential o f about 200-400 kg sand m(-2) yr(-1) at natural population densities u nder favorable flow conditions. We consider the possible implications of the bioturbation potential of stream invertebrates for ecology (hab itat quality and disturbance) and hydrology (sand transport and stabil ity of coarse stream bottoms), which call for joint research on this n ovel role invertebrates play in the functioning of stream ecosystems.