Recent research has shown that several phytoplankton taxa, especially dinoflagellates, are mixotrophic. This ability plays a key role in the structuring of the oceanic food web, hence the quantitative estimation of mixotrophic activity is fundamental for food web modelling. However, we currently lack a robust method to quantify the occurrence of mixotrophy for ¿large¿ phytoplankton (>30µm) in environmental samples. Here we explore the use of the Lysotracker fluorochrome (Molecular Probes), which stains acidic organelles such as lysosomes, to gain insight to the trophic status of a cell. Lysotracker is a non-toxic live stain, thus no fixation of the sample is necessary and the destruction of delicate cells through the fixation process can be avoided. Our aim was to quantify the number of mixotrophic organisms in microplankton communities in situ. We successfully applied the stain to quantify mixotrophic organisms in cultures using epifluorescence microscopy. We are currently adapting this method for environmental samples, both in comparison to and in a combination with DAPI (nuclei visualization). High levels of background noise present the last technical challenge for implementation. Our results suggest that the use of Lysotracker may be a viable way for quantifying the level of mixotrophy in plankton communities

2nd International Ocean Research Conference, One planet one ocean, 17-21 November 2014, Barcelona, Spain

Peer Reviewed