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This paper describes the PREI (Posidonia oceanica Rapid Easy Index), a method used to assess the ecological status of seawater along Mediterranean French coasts. The PREI was drawn up according to the requirements of the Water Framework Directive (WFD 2000/60/EC) and was tested on 24 and 18 stations in PACA (Provence-Alpes-Côtes d'Azur) and Corsica, respectively. The PREI is based on five metrics: shoot density, shoot leaf surface area, E/L ratio (epiphytic biomass/leaf biomass), depth of lower limit, and type of this lower limit. The 42 studied stations were classified in the first four levels of status: high, good, moderate and poor. The PREI values ranged between 0.280 and 0.847; this classification is in accordance with our field knowledge and with our knowledge of the literature. The PREI was validated regarding human pressure levels (r(2)=0.74). (http://eurex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2000:327:0001:0072:EN:PDF).

In this study, living (Rose Bengal stained) foraminiferal faunas from 31 stations along the entire French Mediterranean Sea coast except Corsica have been analysed. In the context of the Water Framework Directive, the aim was to develop a biotic index to evaluate the benthic ecosystem quality. Therefore, different faunal parameters (diversity indices, wall structure proportion, and indicative species groups) have been tested to determine their relevance as indicators of environmental conditions. The best results are obtained with a biotic index based on the relative proportion of stress-tolerant taxa. For ecosystem quality evaluation, it is essential to distinguish between natural and anthropogenic eutrophication phenomena. In order to do so, we applied a correction on our biotic index, using the expected percentage of stress-tolerant species in natural environments, in function of sediment grain size (percentage <63 μm). Finally, a comparison of the different faunal parameters calculated for two different sediment intervals (0-1 and 0-4 cm) indicates clearly that the analysis of the uppermost centimetre of the sediment is sufficient to obtain relevant information needed for bio-monitoring purposes. Highlights ► Development of a biotic index based on benthic foraminiferal faunas. ► Discriminate between natural and anthropogenic eutrophication. ► Relevance of foraminiferal parameters for the development of biotic index. ► Inventory of living benthic foraminiferal faunas of the French Mediterranean coast. ► Restrict faunal analysis to the first cm of sediment for bio-monitoring studies.

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