Interaction between the effects of Substratun, Velocity and location on Stream Benthos: and experiment

Abstract

Patches of large and small pebbles were created in three riffles (fast current velocities) and three pools (slow velocities). It was expected that patches with different sizes of pebbles in the two velocity regimes would vary in the entrapment of fine sediments and organic matter, which in turn would result in differences in benthic community structure. This was not the case, for although deposition of fine material was greater in pools, there were appreciable location-specific differences in the fauna unrelated to the variables monitored in the experiment. Functional feeding groups did not respond predictably to the distribution of detritus. Generally, the community was least influenced by substratum size, with any differences being inconsistent across locations. Most other substratum effects were attributable to the presence of epilithon on undisturbed control patches. Velocity was the most influential factor, with riffles having higher total abundances and higher species richness. Some taxa showed strong location- specific differences. At the level of a small patch of pebbles, the colonization dynamics of the fauna are probably a mixture of species- and location-specific dispersal and selection mechanisms. At larger spatial scales, however, community structure is more predictable, with pools differing substantially from riffles.