Effects of macrophyte architecture and leaf shape complexity on structural parameters of epiphytic algal community in a Pampean stream

Abstract

Habitat heterogeneity is one of main factors determining distribution of organisms, and vegetation is of primary importance in shaping structural environment in aquatic systems. The effect of macrophyte complexity on macroinvertebrates has been well researched, however, much remains to be revealed about influence of complexity on epiphytic algae. Here we used fractal dimension to study effect of complexity at two scales, macrophyte architecture and leaf shape, on several parameters of epiphytic algal community (number of individuals, biomass, taxon richness, and diversity) in a Pampean stream. Four submerged macrophyte species with different complexities and associated algae were sampled in late spring, summer, and autumn. Important differences were found in fractal dimension of whole plant and leaves among macrophyte species. Particulate organic matter and chlorophyll-a associated positively to leaf fractal dimension, but not to plant fractal dimension, partially supporting the hypothesis of a positive effect of macrophyte complexity on periphyton biomass. No association was found of fractal dimension with algal abundance, taxon richness or diversity. Complementary, a mesocosms experiment was performed with plastic imitations of different plant fractal dimension. After four weeks, there were differences in chlorophyll-a and autotrophy index between treatments which suggested a positive effect of complexity on autotrophic periphyton biomass. Differences in plant fractal dimension effect between sampling and experiment were attributed to differences in environment and algal community between stream and experimental trays. Results indicate that well-known positive effect of macrophyte complexity on macroinvertebrates might be partially explained by a positive effect of complexity on periphyton biomass.