Response of biofilm growth to experimental warming in a temperate stream

Abstract

Biofilm is an important component of small streams, and it is highly sensitive to variations in water temperature. Therefore, it is expectable that the warming predicted for this century will be reflected in its communities. In this study, we investigated the effects of experimental warming on biofilm growth in a small forest stream in Central Portugal. The stream was longitudinally divided in two halves, both at ambient temperature during ambient period; the following months (warmed period), one stream half remained at ambient temperature (control half) and the other half was experimentally warmed by ~3 °C (experimental half), following a before‐after control‐impact design. Biofilm variables (biomass, chlorophyll‐a and chlorophyll‐c concentrations, autotrophic index, and diatom density) were determined from epilithic samples collected from both stream halves three times during the ambient period and five times during the warmed period. The experimental warming led to a significant increase in biomass, chlorophyll‐a, chlorophyll‐c concentration, and diatom density, especially in the winter months. Future warming, especially during the colder months, may thus stimulate biofilm growth, which may strengthen the autotrophic pathways of these systems traditionally based on detritus.