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Field monitoring and trophic modelling as management tools to assess ecosystem functioning and the status of high trophic level predators in Mediterranean marine protected areas

Abstract : The overexploitation of high trophic level predators (HTLP) may trigger trophic cascades, often leading to a simplification of marine food-webs and reducing their resilience to human impacts. Marine protected areas (MPAs) can foster increases of HTLP abundance and biomass, but long time frames are needed to observe a recovery, when possible, of lost trophic interactions. This PhD aimed to propose integrated management-tools to monitor HTLP recovery and the restoration of trophic interactions in Mediterranean MPAs, and to evaluate the effectiveness of these tools at assessing fishing impacts upon HTLP and the associated food-web. Two often distant approaches were combined: field monitoring and food-web modelling. First, to survey the fish assemblage, we proposed to improve the traditional underwater visual census technique of one size-transects with variable size transects adapted to fish mobility. This improvement increased the accuracy of density and biomass estimates of HTLP at three Mediterranean MPAs. We then evaluated the potential of food-web modelling with the Ecopath with Ecosim and Ecotroph approach as a tool to inform ecosystem-based management in Mediterranean MPAs. We proposed a standard model structure as the best compromise between model complexity, feasibility of model construction in terms of data collection, and reliability of model outputs. Key functional groups for which local accurate biomass data should be collected in priority in order to get reliable model outputs were identified.
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https://tel.archives-ouvertes.fr/tel-01745467
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Giulia Prato. Field monitoring and trophic modelling as management tools to assess ecosystem functioning and the status of high trophic level predators in Mediterranean marine protected areas. Agricultural sciences. Université Nice Sophia Antipolis, 2016. English. ⟨NNT : 2016NICE4000⟩. ⟨tel-01745467⟩

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