Nutrient-induced fluorescence transients in diatom-bacteria biofilms suggested the possible application of marine biofilms in monitoring nutrient disturbance

•The diatom-bacteria biofilms selectively used nitrogen sources.•The fluorescence transients of the biofilms occurred when ammonium was added.•The changes in fluorescence were related linearly to the ammonium concentrations.•The biofilms have the potential to monitor the disturbance of ammonium in water.