Environmental drivers of mixotrophy and its impact on the plankton metabolic balance

Mixotrophy is a successful nutritional strategy as it provides marine micro-organisms with the ability to combine photoautotrophy and phago-heterotrophy, and therefore use alternative forms of carbon uptake (1). Thus, mixotrophs contain a functional chloroplast and can additionally graze on prey to obtain their carbon. This alternative nutritional pathway is advantageous under light- and nutrient-limited environments, where mixotrophs get a nutritional advantage compared to strict autotrophs or heterotrophs (2). There is limited knowledge on the influence of mixotrophy on the relationships between chlorophyll-a and primary production, on the net community production, and therefore, on the carbon transfer to higher trophic levels and the ecosystem functioning. A recent study in temperate coastal waters showed that mixotrophy can alter the relationship between primary production estimates and chlorophyll-a concentration, and this change could introduce biases to the primary production estimations from satellites and gliders (3). However, there is currently no quantification of the variability of this relationship, and whether it is similar for different organisms (bacteriophages, mixotrophic ciliates and coccolithophores) or the influence of environmental conditions. This project will address these questions combining laboratory work and numerical models.