From Tswett to identified flying objects: A concise history of chlorophyll a use for quantification of phytoplankton

The unique optical characteristics of chlorophyll a (Chl a) and the relatively easy procedures for its isolation and quantification are the reasons that Chl a is quite likely the most frequently measured biological substance in aquatic research. Development of analytical methods of quantification and commercialization of optical instruments were the impetus for the widespread measurement of Chl a in all aquatic environments. Chl a is often utilized as a proxy for the assessment of phytoplankton biomass, although it is by no means synonymous with phytoplankton biomass, usually expressed in terms of cellular carbon content or fresh weight. The modification of light reflected from a water surface by Chl a can be quantified in different types of water, and thus provides a basis for remote sensing of that pigment. Reflectance information recorded by satellite-carried sensors enables mapping of Chl a distribution, and due to the high frequency of data collection provides a database for estimation of phytoplankton dynamics over large areas, up to global coverage.