Effects of three different grazers at high densities on algal communities.

Abstract

This study examined the effects of three dominant grazers, Glossosoma nigrior and Protoptila tenbrosa, which are caddis flies, and Elimia sp., a snail, at high densities on algal communities in artificial streams. In the areas from which this species are found in high numbers, the algal standing crop is very low. Both Glossosoma and Elimia removed a considerable percentage of the algae, but at their approximated actual densities, they did not remove all possible algae. The remaining algae could be important in determining what other species coexist in the same community. Both grazers seemed to remove the algae in patches but this was not conclusively shown. Protoptila, on the other hand, did not remove very much of the algae. The conditions of this experiment may not have been suitable for it or else the Protoptila may have been going through a dormant period.