A challenge for the sustainable development of marine aquaculture is to determine the appropriate level of production that respects the ecological carrying capacity (ECC) of the receptor ecosystems. Most environmental thresholds have only been defined for temperate ecosystems, and very few studies have quantified impact thresholds in tropical environments. To fill this gap, my PhD will 1) qualify the response of benthic habitats to organic enrichment in a tropical case study, 2) identify indicators of the effects of aquaculture impact on the benthic compartment and determine thresholds via a meta-analysis, and 3) develop an impact module integrated into the MOCAA model.
This presentation exposes results of a sampling campaign conducted in 2022 in Martinique. To quantify discharges from a fish farm ( S. ocellatus ), particle traps were deployed parallel and perpendicular to the main current direction at 0, 25, 50 and 150 m from the cages. Hydrodynamics and zootechnical data were also collected to model the environmental impact of the farm with the MOCAA model. Grab samples were taken to analyze the structure and diversity of benthic communities, supplemented by sediment cores to analyze sediment physico -chemical parameters. Isotopic signatures of each compartment (food, sediment in traps, sediment) were also carried out to trace fish farming waste and determine sources of OM content.
Initial results of this study show that s edimentation rates are significantly higher at station 0 m in the main current direction , compared to other stations. Conversely, OM content in sediments was not significantly different between stations and transects. Isotopic signatures of OM from particle trap samples ranged from -22.45 ± 0.57 to -18.77 ± 0.17 ‰ (δ13C ) and 3.18 ± 0.02 to 4.89 ± 0.29 ‰ (δ15N) (Fig.1) . S amples follow a clear gradient along both transects, with a depletion in δ13C and an enrichment in δ15N at 0 m. A similar but less marked pattern was also observed for δ13C and δ15N values of OM from the grab samples in the main current direction. Ongoing analyses (benthic communities structure, farm waste modelling ) are in progress to explain and precise these observations.