Stability of size distributions of benthic diatoms in lotic ecosystems

Body size distributions have been explored in a wide range of terrestrial and aquatic organisms, and show that densities decrease log-linearly with increasing body size. Moreover, current knowledge of algal ecology suggests that the slopes and intercepts of these relationships should vary with environmental characteristics. The purpose of this study was to describe the body size distributions of stream benthic diatoms. The specific objectives were: (1) to evaluate whether body size distributions of diatoms display a log-linear decrease with increasing body size, similar to other organisms, (2) to evaluate if the slopes of diatom body size distributions vary as a function of trophic status, and (3) to evaluate if average body size is related to trophic status. The body size distributions of 29 benthic diatom assemblages sampled along an agricultural gradient were plotted. The size distributions appeared to be very similar, despite variability in pollution levels among sites. The slopes did not vary significantly between the 29 sites. There was also no relationship between TP concentrations and diatom biovolume. These results suggest that small diatoms are more abundant than large diatoms in stream systems, and that the distribution of body size in these organisms is independent of nutrient conditions.