Diversity of benthic microalgae in response to colonization time and eutrophication

The factors regulating species diversity have received increasing attention in the face of the global biodiversity loss, but are not well understood for unicellular organisms. We conducted in situ experiments in Kiel Fjord in order to analyze the response of microalgal diversity to colonization time and to artificial eutrophication. Diversity decreased throughout colonization time (maximum: 12 weeks), whereas species richness initially increased to about 25 species before it leveled off. The proposed unimodal time course of diversity during succession could not be detected for diversity or species richness. The rapid decrease of evenness indicated a greater importance of algal growth on the substrata compared to the arrival of new species. Artificial eutrophication led to an decrease of diversity, which could be correlated to the supply concentrations of the limiting nutrient: P in spring, N in summer and Si in the presence of high concentrations of N and P. The decrease was due to an increased dominance of few species (i.e. reduced evenness), whereas species richness was not or positively correlated to nutrient supply. Species richness was negatively correlated to evenness and diversity measures. Thus, species diversity indices are useful response variable to measure environmental effects on local periphyton communities. (C) 2000 Elsevier Science B.V. All rights reserved.