Acquisition de données complémentaires aux dénombrements, avec les techniques d’analyses pigmentaires et de diversité génétique. Etat d’avancement et premiers résultats. Action Indice Composition. Livrable n° AIV. Rapport final, 16 juillet 2014.

Studies on phytoplankton community diversity cannot be limited microphytoplankton (cells>20 ìm), it is indeed necessary to take into account also the nano (3-20ìm) picophytoplankton (<3 ìm) components. In the frame of this work aimed at studying temporal phytoplankton community diversity two complementary methodologies of phytoplankton sample analysis, pigment and genetic (metarbarcoding) diversity, have been used as alternative to routine morphological analysis carried out at light microscopy. The REPHY station (047-P-016 Concarneau Large) off-shore the Concarneau Bay has been sampled during the annual highest phytoplankton production (March-July 2012) with a frequent sample interval strategy (twice per week). Results obtained by both pigment and metabarcoding analyses showed a good resolution of all phytoplancton size classes (micro-, nano-, picophytoplankton) diversity, from a groups/class level (pigments) to a species/genetic clades taxonomic resolution (metabarcoding). Size class dynamics of phytoplankton communities is clearly controlled by the high nutrient concentrations measured during the study period, with pico-nano phytoplankton dominating in periods of nutrient depletion. The metabarcoding approach allowed the identification of protistan groups characteristic of all size classes and showed that diversity of each compartments evolve independently. Sequences of piconanophytoplankton together represent in most of the samples at more than the 50% of total identified OTUs (Operational Taxonomic Units), suggesting that pico- and nanophytoplakton communities are dominant compartments of the phytoplankton of the Concarneau Bay.