Simulation experiments to elucidate variable fluorescence as a potential proxy for bulk microalgal viability from natural water, sediments and biofilms: Implication in ships ballast water management

Abstract

The variable fluorescence fluorometry measuring microalgal biomass (initial fluorescence - F0, a chl-a proxy) and photosynthetic efficiency (Fv/Fm) 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 Fv/Fm 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 (Fv) 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 Fv and σPSII (functional-absorption-cross-section of photosystem II) along with F0 and Fv/Fm 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.