Biotic indices, which reflect the quality of the environment, are widely used in the marine realm. Sometimes, key species or ecosystem engineers are selected for this purpose. This is the case of the Mediterranean seagrass Posidonia oceanica, widely used as a biological quality element in the context of the European Union Water Framework Directive (WFD). The good quality of a water body and the apparent health of a species, whether or not an ecosystem engineer such as P. oceanica, is not always indicative of the good structure and functioning of the whole ecosystem. A key point of the recent Marine Strategy Framework Directive (MSFD) is the ecosystem-based approach. Here, on the basis of a simplified conceptual model of the P. oceanica ecosystem, we have proposed an ecosystem-based index of the quality of its functioning, compliant with the MSFD requirements. This index (EBQI) is based upon a set of representative functional compartments, the weighting of these compartments and the assessment of the quality of each compartment by comparison of a supposed baseline. The index well discriminated 17 sites in the north-western Mediterranean (French Riviera, Provence, Corsica, Catalonia and Balearic Islands) covering a wide range of human pressure levels. The strong points of the EBQI are that it is easy to implement, non-destructive, relatively robust, according to the selection of the compartments and to their weighting, and associated with confidence indices that indicate possible weakness and biases and therefore the need for further field data acquisition.
International audienceThis study highlighted that the management of coastal fish assemblages still requires to upgrade and involve not only the approach of controlling catches but also in addition the management of all the essential habitats frequented during the different stages in the life cycle of these species. On the basis of a specific case study, the nurseries of the Sparidae fishes of the genus Diplodus (white seabream) in the area of the Calanques National Park (Marseilles; north-western Mediterranean), the present article proposes a conceptual scheme to guide coastal managers in following a seascape scale approach while using the tools they dispose of. This case study furthermore enables us to make practical recommendations applicable to the statutory and contractual management of the whole of the Mediterranean coastal zone
. Cross-taxon congruence in the rarity of subtidal rocky marine assemblages: No taxonomic shortcut for conservation monitoring. Ecological Indicators, Elsevier, 2017, 77, pp.239-249 investigating the distribution of rarity among subtidal rock bottom phyla; (2) searching for 27 potential surrogate phyla with a cross-taxon congruence approach based on their rarity; (3) 28proposing an appropriate multi-phyla indicator to evaluate the importance of subtidal rocky 29 habitats for conservation. We analysed the distribution of 548 species belonging to 8 phyla 30 sampled in 137 assemblages in subtidal rocky areas located around Brittany, Western France.
31We applied the Index of Relative Rarity, a flexible method which fits rarity weights to species 32 depending on their respective phyla. We found only weak congruence in rarity patterns among 33 phyla, which prevented any attempt to identify surrogate phyla. This finding has important 34 implications for the conservation of subtidal rocky habitats as it means that there is no shortcut 35 to monitor their rarity: working on a subset of phyla would imply a biased evaluation of 36 biodiversity. Consequently, we propose a multi-phyla Index of Relative Rarity combining all 37 phyla which allowed us to successfully describe rarity patterns across all sampled sites. 38 39
Key-words 40Occurrence-based rarity, subtidal conservation, rare species, Brittany 41 42 3
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