Microbes in aquatic biofilms under the effect of changing climate

Abstract

The effects of climate change on aquatic biofilm structure and function is difficult to predict mainly due to biofilms being complex and dynamic assemblages of microorganisms. We review observed patterns of the effects of warming and desiccation on biofilms. Commonly observed effects of warming on biofilms include changes in the autotrophic community composition and extracellular polymeric substances, stimulation of the heterotrophic community, and changes in the microbes, protozoa and small metazoans densities and composition. The magnitude of the temperature effects depends on the biofilm successional stage, resources availability, community composition and interactions within communities including top-down effects. Temperature also affects biofilm functioning by direct control of biological activities and by selecting adapted taxa, which provide feedback on activities. Biofilm photosynthesis, respiration, denitrification and extracellular enzyme activities show differential sensitivity to temperature. Results suggest a significant effect of temperature on the nitrogen cycling and a link between the specific community composition and the biofilm temperature sensitivity. On the other hand, desiccation may produce more permanent changes on the biofilm microbial community composition than on extracellular enzyme activities, the effects also depending on species specific sensitivity and biofilm structure (such as the content of extracellular polymeric substances). At the ecosystem level, both factors (warming and desiccation) may coincide in time, but few studies have looked at the drought?temperature interactions on aquatic biofilms. Future trends might include multistress and short- and long-term experimental approaches. Measurements of carbon and nitrogen budgets are needed to quantify the effects of biofilm metabolism on ecosystem nutrient cycling and, at the same time, to improve biofilm models