Abstract
Marine aquaculture has a high growth potential, useful for meeting current and future populations’ food needs. Aquaculture activity, including the stage of production and those upstream and downstream the value chain, however, is responsible for potential environmental impacts on local (e.g. benthic impact) or global (e.g. impact on climate change) ecosystems. To minimize these impacts, it is necessary to develop environmental analysis methods with a holistic approach. The general objective of this thesis was to design a method to assess environmental impacts at different spatial scales (local, regional, global) by combining modeling tools at several organizational scales (individual, farm, sector) and scenario analysis. This method was tested on a case study of red drum (Sciaenops ocellatus) farming in Mayotte lagoon. Three farm scenarios were built based on field surveys. The FINS model was developed to simulate farm operations in these scenarios and to estimate farm emissions (solid and dissolved). Solid waste dispersion and deposition were simulated with the NewDEPOMOD model for site scenarios covering different hydrodynamic conditions in a zone of the lagoon. Farm scale, farm management choices and site current intensity are the main factors that determined the level of emissions and/or solid waste dispersion and thus the potential benthic impact. A life cycle assessment (LCA) was performed to compare global impacts of one of the monoculture farm scenarios to those of an integrated multi-trophic aquaculture (IMTA) system combining the deposit-feeder Holothuria scabra and fish farming. This IMTA system demonstrated low bioremediation capacity for solid waste and global impacts at levels similar to those of the monoculture system, due stocking-density limits for the deposit-feeder compartment. This multiscale environmental impact assessment made it possible to identify the key factors determining systems’ environmental sustainability and the factors for which actions could be proposed.