Résumé: By the end of the twentieth century, many of the coastal lagoons along the French Mediterranean coast showed insufficient water quality and degraded ecosystem states due to anthropogenic impacts. Among these, nutrient over-enrichment, resulting in eutrophication, has been a major concern. The Water Framework Directive of the E.U. (WFD) has initiated public action to improve their water quality and ecosystem state using an approach rooted in restoration ecology. Here we analyse how this has been applied for the coastal lagoons in South France, considering eutrophication as an example of ecosystem degradation and oligotrophication as the corresponding way for ecological restoration of the eutrophied coastal lagoons. Oligotrophication trajectories, initiated by the reduction of external nutrient loading, have resulted in a quick recovery (i.e. within 3 years) of integrative water column variables (Chlorophyll a, total N and P). The biomass of phytoplankton dropped very quickly showing concomitant changes in their community compositions. Starting from hypertrophic systems, the oligotrophication trajectory is described by a sequence of three ecosystem states dominated respectively by (i) phytoplankton with bare non-vegetated sediments, (ii) opportunistic macroalgae, (iii) angiosperm and perennial macroalgae, punctuated by regime shifts between these ecosystem states. Nevertheless, the latter regime shift has not been observed for the most degraded ecosystems after 10-years oligotrophication. The N and P accumulated in sediments during eutrophication may also retard the ecological restoration. In shallow freshwater lakes, the phytoplankton-dominated and the angiosperm-dominated states are also characteristic for highly-degraded and fully-restored ecosystems states, respectively. In contrast, opportunistic macroalgae do not bloom in these systems. Hence, the multiple stable state model, used successfully for these lakes, cannot be applied straightforwardly for coastal lagoons. To be successful, ecological restoration should consider societal questions as according the DPSIR framework it typically is a response of society. Local citizens and highly-involved stakeholders strongly value the coastal lagoons and attribute very high importance to their regulating ecosystem services (ESs). Different stakeholder profiles are related to different perceptions and appreciations of cultural ESs. Finally, more studies are needed to asses compatibility and incongruencies between the WFD and the Habitats directives, as both apply to coastal lagoons.

Résumé: The objective was to compare water quality and fish growth and mortality in a pilot scale recirculating system (RS) and a control tank in flow through system (FTS). The RS was designed after the Danish Model Trout Farm and operated with a make Lip Water renewal rate of 9 m(3) kg(-1) of fish produced. RS water quality did not decrease significantly with water flow rate decrease in the RS. During the experiment, the RS water treatment system presented solids removal efficiency of 59.6 +/- 27.7% d(-1), ammonia oxidation of 45 +/- 32 g m(-3) d(-1), oxygenation yield of 392 +/- 132 g of O-2 kWh(-1) and CO2 degassing of 23.3 +/- 11.9% pass(-1). In the RS, nitrite concentration was 0.15 +/- 0.07 mg l(-1), close to the toxicity threshold; a N-2 supersaturation phenomenon was measured, probably due to the air injection depth. The biofilter and sedimentation area management has to be improved to avoid Organic matter decomposition and release of dissolved elements. Even if no N-2 over-saturation apparent effect on fish performance and aspect were detected, the airlift depth has to be modified in the case of industrial development of the RS. Some improvements of the water treatment system, especially on the airlift and sedimentation area, are suggested. Concerning fish growth, no significant differences were observed between the RS and the FTS. No pathologies were detected and cumulative mortality rates (0.1%) were similar to the farm's Usual data. There were no significant effects of water flow rate decrease in the RS on fish performance and energy savings were recorded to be 0.7 kWh kg(-1) of fish produced between RS1 and RS2. The global energy cost of the RS was 3.56 kWh kg(-1) of fish produced (0.107 (sic) kg(-1) of fish produced). Even if the energy consumption of the water treatment system can be improved, the results confirm that recirculating system can be used for industrial trout On growing, without fish performance deterioration. (C) 2009 Elsevier B.V. All rights reserved.

Résumé: The importance of heterotrophic bacteria relative to phytoplankton in the uptake of ammonium and nitrate was studied in Mediterranean coastal waters (Thau Lagoon) during autumn, when the Mediterranean Sea received the greatest allochthonous nutrient loads. Specific inhibitors and size-fractionation methods were used in combination with isotopic 15N tracers. NO3 − and NH4 + uptake was dominated by phytoplankton (60 % on average) during the study period, which included a flood event. Despite lower biomass specific NH4 + and NO3 uptake rates, free-living heterotrophic bacteria contributed significantly (>30 %) to total microbial NH4 + and NO3 − uptake rates in low chlorophyll waters. Under these conditions, heterotrophic bacteria may be responsible for more than 50 % of primary production, using very little freshly produced phytoplankton exudates. In low chlorophyll coastal waters as reported during the present 3-month study, the heterotrophic bacteria seemed to depend to a greater extent on allochthonous N and C substrates than on autochthonous substrates derived from phytoplankton.