Premières propositions pour un indice de composition du phytoplancton, basé sur les résultats de cytométrie en flux. Action 3 - Indice Composition - Livrable 2. Rapport final, mars 2016

The European Union Water Framework Directive (WFD) refers to phytoplankton as one of the biological quality elements that should be regularly monitored and evaluated thanks to three ecological indices: biomass, abundance and composition. The first two have already been defined, but the third one has not yet been proposed in the English Channel - Atlantic zone. The construction of a composition index must consider the diversity of all the phytoplankton organisms. As the microscopic counts concern only the micro-phytoplankton, it is necessary to use additional information which concerns the nano- and pico-phytoplankton, of great importance in the phytoplankton diversity. These components of the phytoplankton can be measured by different complementary techniques: traditional or scanning flow cytometry, HPLC pigments analysis, spectral fluorescence, FlowCAM / PhytoImage, genetic biodiversity. In order to define the indicators for the WFD while considering the phytoplankton dynamics in all the marine waters, it is necessary to use high resolution measures, thanks to the development of new sensors and data analysis tools. The actions described in the present report were carried out in collaboration between the Laboratory of Oceanology and Oceanography from Wimereux (CNRS UMR 8187 LOG) and the laboratory IFREMER LER/Boulogne, and the participation of the laboratories DYNECO/PELAGOS, DYNECO/VIGIES from IFREMER, LISIC-ULCO from Calais, as well as the partners of the DYMAPHY project. The comparison of the results obtained by different techniques of phytoplankton assessment was described in the previous 2013 A.II and A.III reports, in which the analysis of the first comparisons of measurements carried out within the INTERREG IVA “2 Mers” DYMAPHY project during common cruises or on observation and monitoring sites in Eastern English Channel were presented. In the present report, the aim was to propose a set of analysis which could help building a phytoplankton composition index based on the results of automated flow cytometry. Here the focus is made on a part of the total results (see below). The data from regular monitoring not analysed yet will contribute to move towards the proposition of a phytoplankton composition index based on flow cytometry measurements. The monitoring of phytoplankton distribution carried out at both high spatial resolution during international oceanographic cruises (DYPHYMA- DYMAPHY project) and high temporal resolution during regular observation cruises (Wimereux-Slack transects), permitted to bring out the complexity of proliferation/accumulation, dominance changes from a phytoplankton group to another, responding to environmental changes. These techniques, when used at high resolution, will allow a better understanding of the phytoplankton diversity and will make it possible to move towards the proposition of a composition index for the WFD, but will also help bringing some important information, that could be used to estimate the ecological quality of all marine waters, in the frame of the Marine Strategy Framework Directive (MSFD).