Variability of heterotrophic activity in Mediterranean stream biofilms: A multivariate analysis of physical-chemical and biological factors

Abstract:

Environmental factors responsible for inter-site and temporal variations in extracellular enzymatic activities in benthic biofilms were studied in three Mediterranean streams. Results from canonical correlation analysis suggest that ionic content of the water and chlorophyll a content of biofilms (algal biomass) were the main factors accounting for the variability in extracellular enzyme activity of the biofilms in these streams. Water temperature was not an important factor accounting for differences among streams, while nutrient concentration played a role only in special situations such as periods when flow stops. Episodes of flow cessation and high discharge greatly affected the extracellular enzymatic activities. Biofilms differed in their efficiency in the use of polysaccharides (defined as the activity of $\beta$-glucosidase and $\beta$-xylosidase per bacterial cell). Biofilms at the site showing high nutrient concentrations (Ter River) were the least efficient, while those occurring at lower nutrient concentrations (La Solana and sandy sediments of Riera Major) were the most efficient. The highest efficiency was associated with stromatolitic communities in La Solana. The epilithic biofilms of Riera Major showed a lower efficiency than biofilms on sand in the same stream, suggesting that biofilm type may be another factor inducing variation in biofilm activity.