Validation de l’indice composition IC Medit dans des masses d’eau côtières méditerranéennes caractérisées par un gradient croissant d’eutrophisation

The aim of this study is to show the current status of the development and use of the new IC Medit
phytoplankton composition index as a sub-metric within the phytoplankton quality element in assessing phytoplankton quality in Mediterranean coastal waters. IC Medit uses pigment concentrations determined by HPLC for assessing phytoplankton composition. Focusing on coastal waters of Corsica, we (i) described the seasonal succession of the main phytoplankton groups in reference conditions, (ii) studied responses of phytoplankton groups to well identified drivers, (iii) assessed the shift of the seasonal succession of phytoplankton groups from the reference conditions in impacted areas, (iv) revealed pressure / impact relationships between nutrients
and pigments, and (v) established guidelines for sampling and IC MEDIT implementation.
IC Medit is an indicator that improves the information provided by chl a in relation to anthropogenic pressures. It provides useful information on water quality, and could be used for management purposes. Nevertheless, due to the lack of information about the relationship between phytoplankton composition and pressures in highly impacted areas, boundary conditions are still to be defined. This should be done in collaboration with statisticians.