Structural Characteristics of Benthic Algal Communities in Laboratory Streams

Abstract

Effects of light intensity and current velocity on the species composition and ecological properties of communities of benthic algae were investigated in laboratory streams. Of the 15 diatom taxa studied, only Melosira varians, Meridion circulare, and Navicula radiosa were more abundant in streams receiving 700 ft—c of illumination than in those receiving 150 ft—c. Achnanthes exigua, A. minutissima, Meridion circulare, Rhoicosphenia curvata, and Navicula radiosa were indifferent to current velocity, while current velocity had a positive effect on the abundance of Nitzschia linearis, Achnanthes lanceolata, Navicula cryptocephala, N. minima, N. seminulum, Synedra ulna, Gomphonema parvulum, G. angustatum, Cocconeis placentula, and the lanceolate Nitzschia. Melosira varians exhibited a negative response to current and was more abundant in standing water. Of the six taxa other than diatoms, Anabaena variabilis and Tribonema minor were more abundant in streams at the higher light intensity, but only one species, Phormidium retzii, was more abundant in streams with a current than in standing water. At a particular season, light intensity, and current velocity, conditions in a laboratory stream allow the establishment of an algal community with a more or less unique species composition and a characteristic biomass, pigment concentration, and increment of export. In order to understand the factors which influence productivity in these communities, it is necessary to have some knowledge of the autecologies of the community constituents and the mechanisms which regulate species composition and diversity of the flora.