Charles Carignan, “Comparing Photosynthetic Efficiency of Freshwater Algal Species in-vitro Using Fast Repetition Rate Fluorometry (FRRF)”
Mentor: Harvey Bootsma, Freshwater Sciences
Poster #36

The photosynthetic efficiency of phytoplankton is a primary determinant of the productivity of aquatic ecosystems. Every year marine phytoplankton fixes between 30 and 50 billion metric tons of carbon, roughly half of all global carbon fixation. Fast Repetition Rate Fluorometry (FRRF) is an increasingly utilized technique for measuring phytoplankton nutrient status and photosynthetic efficiency in marine environments, however, there are few studies utilizing this technique in freshwater ecosystems. Being a relatively new method, studies in varying ecosystem types and with multiple species are required to better define the interpretation of the data provided by FRRF. This technique utilizes flashes of light at specific wavelengths, repeated at a high rate, to induce fluorescence of algal cells. This fluorescence value can be used in combination with several equations to provide an estimate of the amount of O2 produced per cross-sectional area of the photosynthetic cells. As O2 is an end product of the photosynthesis reaction, O2 evolution is often used as a proxy for photosynthetic production. Traditionally, rates of primary productivity in phytoplankton are measured by tracing O2 evolution or CO2 assimilation using incubations coupled with either titrations or dissolved oxygen sensors. These techniques offer limitations, such as high cost and labor intensity involved with sample processing and low spatial and temporal resolution, which has led to the need for a simpler and less intrusive method of estimating primary productivity in both coastal and open water ecosystems. This study aims to establish a baseline of photosynthetic efficiency using phytoplankton species from two common genera found in the Laurentian Great Lakes, Navicula (a diatom) and Selenastrum (a green alga), by measuring them in-vitro. These baselines will allow future Great Lakes scientists to make comparisons between natural environments to determine how phytoplankton community composition may affect rates of photosynthetic production.