Reexamination of Methods for Measuring Photosynthesis of Benthic Algae in Flowing Water Systems

We reexamined the critical importance of water motion in measuring algal growth and photosynthetic rates, addressing a significant limitation in traditional static incubation approaches. It presents a comprehensive framework for dynamic measurement methods that better simulate natural hydrodynamic conditions experienced by both macroalgae and other benthic autotrophs. We considered the barrier effects of the diffusion boundary layer surrounding the algae on the fluxes of gases and nutrients across the cellular membrane, and integrates findings demonstrating that flow-enhanced mass transfer of nutrients, inorganic carbon and O2 across diffusion boundary layers can increase photosynthetic performance in macroalgae including the tested Sargassum, Porphyra and Macrocystis species. We provide quantitative comparisons demonstrating that increased velocities of water current can enhance photosynthetic and/or nutrient uptake rates compared to stagnant conditions. The comparative analysis highlights the advantages of flowing water systems in reducing diffusion limitations and better simulating natural environments against the technical simplicity of static methods. We detailed practical methodologies including flow-through system setup and sealed chamber with magnetic stirring techniques for macroalgae, and brush substrate for benthic diatoms. These approaches enable diurnal physiological tracking and reveal saturation responses to increasing water velocities. The methodological framework provides researchers with robust protocols for more accurate assessment of algal photosynthesis and primary productivity in both experimental and applied contexts such as aquaculture, carbon sequestration, and ecological monitoring.