Temporal patterns in epilithic biofilm-relation with a putative allelopathic activity

Temporal patterns in biomass and in the production of inhibitory compounds were assessed for a diatm-dominated epilithic biofilm of a shallow temperate river. Biomass showed a typical seasonal pattern with the development of two peaks of biomass parallel with species successions. Analysis with self-organizing maps (SOM), a non-supervised neural network, indicated that species composition of phototrophic assemblages was completely explained by environmental parameters during the low-biomass period. When epilithic biomass was high, these Factors were not enough to explain species composition. This suggests that as the biomass increased, intrinsic parameters took over from extrinsic factors in the regulation of biofilm composition. Over the studied period, 70 % of the biofilm samples showed inhibitory activity against one or several of the four indicator phototrophic strains tested in the bioassays. The presence of inhibitory Compounds was not correlated to biofilm biomass. The Occurrence of several patterns of inhibitory activity Suggested the implication of different compounds or mix of compounds, certainly linked to various compositions of algal assemblagges. The SOM analysis underlined putative relationships between the Occurrence of certain species and the presence of an activity inhibiting one of the indicator strains. This indicates potential targets or producers of the implied compounds. To our knowledge, this study followed for the first time the temporal dynamics of inhibitory activity in a biofilm. e frequent presence of inhibitory Compounds is in agreement with the hypothesis that biofilms are auspicious Systems for the development of allelopathic interactions. and provides new insights for further research oil allelopathic interactions in benthic phototrophic systems.