The Effects of Grazing by Snails on Community Structure of Periphyton in Laboratory Streams

Abstract

The effects of grazing by snails on community structure of periphyton were studied in laboratory streams. The levels of grazing studied caused slight reduction in standing crop, significant increase in chlorophyll a concentration, reduction in pigment diversity and no effect on species diversity. Grazing did not affect instantaneous rates of accumulation of oven-dry weight, ash-free weight, or ash-free percentage of oven-dry weight. Pigment diversity and species diversity were positively correlated. Oven-dry weight per unit chlorophyll a was reduced by grazing, but ash-free weight per unit chlorophyll a was not affected. Grazing had no effect on the percentage of chlorophyll a in ash-free weight.