• Sciences de l'environnement/Biodiversité et Ecologie
  
• Sciences de l'environnement
  
• Sciences du Vivant
  
• Planète et Univers/Océan, Atmosphère
  

A conceptual model was constructed for the functioning the algae-dominated rocky reef ecosystem of the Mediterranean Sea. The Ecosystem-Based Quality Index (reef-EBQI) is based upon this model. This index meets the objectives of the EU Marine Strategy Framework Directive. It is based upon (i) the weighting of each compartment, according to its importance in the functioning of the ecosystem; (ii) biological parameters assessing the state of each compartment; (iii) the aggregation of these parameters, assessing the quality of the ecosystem functioning, for each site; (iv) and a Confidence Index measuring the reliability of the index, for each site. The reef-EBQI was used at 40 sites in the northwestern Mediterranean. It constitutes an efficient tool, because it is based upon a wide set of functional compartments, rather than upon just a few species; it is easy and inexpensive to implement, robust and not redundant with regard to already existing indices.

Where seaweed forests meet animal forests: the examples of macroalgae in coral reefs and the Mediterranean coralligene ecosystem

Biotic indices, which reflect the quality of the environment, are widely used in the marine realm. The Posidonia oceanica seagrass meadow is a benthic sublittoral habitat characteristic of the Mediterranean Sea. The Ecosystem-Based Quality Index (EBQI) is based upon the overall functioning of the Posidonia oceanica ecosystem, from primary producers and the litter to top predators. It is compliant with the Marine Strategy Framework Directive (MSFD) of the European Union (EU). It provides managers with a response that is very different from that of the indices only based upon the key species P. oceanica and a few affiliate species. While the species-based indices are mainly designed for assessing the water quality of a waterbody (e.g. pollution), the EBQI provides a picture of the actual status of the ecosystem functioning, including not only pollution but also the whole range of human impacts, from anchoring to overfishing.

tA theoretical model of structure and functioning was constructed for the Mediterranean undersea caveecosystem. This model integrates almost all representative components of the cave ecosystem and givesan idea of their faunal compositions, characteristics and related interactions.This model constitutes the basis of the Ecosystem-Based Quality Index (EBQI) of the European Union’sMarine Strategy Framework Directive, which aims at evaluating the ecological quality of an ecosystem. Itis based on four crucial complementary elements: (i) each component was weighted in accordance withits importance in determining the structure and functioning of the cave ecosystem; (ii) a suite of relevantparameters were defined to assess the ecological state of each component of the cave ecosystem; (iii)these parameters were aggregated into one relevant index, the Cave EBQI (CavEBQI), to summarize thequality evaluation for each cave site; (iv) each value of ecological state is accompanied by a ConfidenceIndex as a measure of its reliability.The CavEBQI was used on 22 Mediterranean undersea caves of France and Italy. Disparities of ecologicalquality were found among caves but most of them ranged from moderate to high ecological quality. Forsome caves, no conclusion can be drawn when our method predicts a poor reliability of the evaluationof their ecological quality.This ecosystem-based evaluation of the quality of undersea caves seems to be a powerful tool, withthe advantage of being based on almost all its components, rather than just on a few species. It is accom-panied by a measure of its reliability, hence it provides a reliable idea of the ecological state of the entireecosystem at each cave site. Monitoring the ecological state of caves and the effects of disturbancesover large geographic and temporal scales is made possible with CavEBQI. Applying the same method toother ecosystems, can provide an integrated view of a marine region, which is essential when addressingquestions about protection, conservation and restoration.

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.