Influence of light and flow on taxon composition and photosynthesis of marine phototrophic biofilm in photobioreactors

In this study, marine biofilms were cultured in a flow-lane, semi-continuous photobioreactor at different irradiances and flows to evaluate their combined effect on biofilms' phototrophic composition and photosynthetic activity. Taxon richness, evaluated by different microscopy techniques, including transmission and scanning electron microscopy, resulted to be heavily reduced from source communities to mature cultures. The strongest decrease was observed for diatoms, which were overcome by cyanobacteria and green algae over time. Photosynthetic performance was investigated by pulse amplitude modulated fluorescence. Irradiance was the main driver of data distribution of the photosynthetic parameters rel.ETRmax and Ik, while flow rate affected alpha and Delta F/ Fm'. The combination of irradiance and flow rate affected Delta F/Fm' reflecting the photosynthetic performance of the most relatively abundant taxa. Higher Delta F/Fm' was attained when cyanobacteria and green algae were dominating, whilst lower Delta F/Fm' when diatoms occurred in the initial phase of biofilm development.