Simulation experiments to elucidate variable fluorescence as a potential proxy for bulk microalgal viability from...

The variable fluorescence fluorometry measuring microalgal biomass (initial fluorescence - F₀, a chl-a proxy) and photosynthetic efficiency (F_v/F_m) has been suggested as a potential tool in ballast-water assessment. In ballast tank, microalgae can be found in contiguous compartments i.e., in water, sediment, and biofilms. Therefore the utility of F₀ and F_v/F_m depends upon proper background corrections, which is straightforward for water samples but not for sediment and biofilms. This study proposes procedures for correcting F₀ values from sediment and biofilms. Irrespective of the saturation flash protocol used on any sample types the outcome of the results from viable and non-viable microalgae will remain same. Stress experiments (continuous darkness and biocide treatments) confirm that variable fluorescence (F_v) can be used as a potential proxy for viable cells as the values were negligible for non-viable cells and increased with an increase in abundance. Through this study, the utility of F_v and σ_PSII (functional-absorption-cross-section of photosystem II) along with F₀ and F_v/F_m in providing additional information on cell-viability and algal-size group during assessment is discussed. The findings will have implications not only from the perspective of ballast water but also in testing/assays of specific interest (e.g. toxicity, water treatments, antifouling) and ecological studies involving microalgae.