Against the backdrop of the functional coupling between autotrophic marine algae and heterotrophic bacteria, possible temperature-related impacts on the bacterial community structure within a brackish mesocosm system were investigated. During simulated algal spring blooms over a temperature gradient, the bacterial community structure was quantitatively and qualitatively analysed, using fluorescent staining, genetic fingerprinting and the CARD FISH method. Additionally, top-down controlling factors like viruses and heterotrophic nanoflagellates were measured as well.