A comparison of community structure and response to grazing between epilithic and epiphytic algal periphyton.

Abstract

Periphyton respond to grazing in different ways depending on the species of algae, the abundance of algae, and the substrate type. The snail, Elimea livescens, reduced biovolumes of large algal taxa, like diatoms, as much as fifty percent. When algal species were considered, the effects of grazing varied from none with Cocconeis placentula to extreme reduction in Navicula radiosa. Elimea livescens grazed the periphyton of rocks more efficiently than it did the peripihyton of Potamogeton richardsonii. This was only ture for what appeared to be a distinguishable upper periphyton layer of predominately diatoms. Perhaps periphyton had a 'refuge' on some part of the macrophyte. Distributions of many algal species were not random with respect to substrate type or substrate parts. Achnanthes minutissima, for example, showed a preference for plant stems. When doing any work with algae it is important to remember the large diversity of microhabitats and species involved.