Authors’ contributions
W.K., N.B. and A. Schwarz performed sampling. R.S. and S.A. performed molecular analyses, S.K. ran high-throughput sequencing, S.A. processed the sequence data. W.K. and P.R. worked on morphological analyses of the diatoms. S.A. and W.K. analyzed the data and performed statistical analyzes. A. Schwalb developed the program (DFG-GRK 2309) that funded this research. S.A. prepared the manuscript with the contributions from all authors. All authors approved the final version.