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Rationale: Carbon (δ13C) and nitrogen (δ15N) stable isotope analysis is a powerful tool to investigate diverse questions in fish ecology, such as their trophic position or migration strategies. These questions appear particularly important to protect endangered European eel. However, elevated lipid content in eel muscle can bias δ13C values, as lipids are 13C‐depleted compared to proteins and carbohydrates. Methods: We measured δ13C and δ15N values of bulk and lipid‐free samples of eel muscle. Lipid‐free samples were obtained after the extraction of lipids with cyclohexane. Lipid‐corrected δ13C values, using five different mathematical equations based on bulk δ13C values, were compared to lipid‐free δ13C values. We also evaluated the effect of lipid extraction on δ15N values. The analyses were based on linear regression performed on 333 individuals captured in nine lagoons and four rivers. Results: Independently to the capture site or habitat (river or lagoon), the predicted lipid‐corrected δ13C values were highly consistent with the measured lipid‐free δ13C values (R2 > 0.90). The application of specific equations for each habitat or capture site only slightly increases these R2 (1.5% or less). The lipid extraction treatment significantly decreased by 0.2‰ the δ15N values compared to bulk samples. Conclusions: Given the excellent prediction of mathematical equations and the small decrease of δ15N values after lipids extraction, we propose to use mathematical correction to estimate δ13C values of eel muscle. As the habitats or sites did not strongly influence the results, the coefficients from our study can be applied to other studies on European eel. [ABSTRACT FROM AUTHOR]

Integrated multi-trophic aquaculture (IMTA) is a solution to biomitigate waste by rearing species from different trophic levels. In European freshwater fishponds, common carp is often produced along with secondary fish species. Developing recycling IMTA systems requires better understanding of the complexity of trophic interactions between fish. Analyses of fatty acid and stable isotopes of carbon and nitrogen are suitable tools for determining food preferences of fish species. Three IMTA systems, including carp, roach, rudd and perch, were investigated in ponds: a semi-intensive (SI) pond in which fish were fed pellets; a semi-intensive pond in which fish were fed pellets, coupled with a lagoon planted with macrophytes (SIC); and an extensive (E) pond in which fish were not fed pellets. In the SI and SIC ponds, fatty acid profiles of carp, roach and rudd were closed to those of pellets. The δ13C and δ15N values of fish confirmed that they mainly fed on pellets, but the diet of roach and rudd also contained natural food sources. In the E ponds, fatty acid profiles of carp, roach and rudd slightly differed but their δ13C and δ15N values were similar. Mixing model indicated that fish from E ponds mainly fed on zooplankton. Regardless of the IMTA systems, fatty acid and stable isotope analyses indicated that juveniles consumed mainly large zooplankton. In the three systems, the FA profile of perch was closed to that of juvenile fish. Mixing model estimated that perch supplemented their diet with large zooplankton and crayfish. In the SI and SIC ponds, the distribution of commercial pellets drove the trophic interactions among fish. In the E ponds, fish had significant feeding overlap due to the limited resources available.

Portmán Bay in Southern Spain is one of the most extreme cases in Europe of anthropogenic impact on the marine ecosystem by the disposal of mine tailings resulting from the processing of sulphide ores. First, the composition and extent of the surficial deposit were investigated from geochemical and metal analysis on high spatial density of sediment samples. Then, a disturbance experiment was conducted in the coastal area off Portmán Bay in order to investigate the potential impact of mining activities on marine ecosystems. Two research vessels were used for that experiment, one performing as a trawler resuspending bottom sediments while the other monitor the behaviour of turbid plumes thus generated and the evolution of their characteristics through time by using a range of acoustic and optical tools together with water and bottom sediment sampling for biogeochemical and metal analyses. The surficial part of the submarine extension of the mine tailings deposit is highly concentrated in As, Cd, Pb, Fe and Zn with peak concentrations adjacent to the present coastline, from where they decrease seawards before reaching average values for the Mediterranean Sea around 50-m water depth. The artificially triggered resuspension of the surface layer of the deposit led to the formation of resuspension plume about 100 m in width and up to 6 m in height. Resuspended plume was composed of fine particles which rapidly aggregated into flocs of 100 μm. While the biggest particles settled rapidly, the finest fraction remained in suspension during at least 3 h. Resuspended sediment and metal concentrations in particles remained at relatively high levels throughout the experiments following triggering. Fe, Pb, and As concentrations in resuspended particles showed a continuous increase while trawling before decreasing in parallel with the settling down of the resuspended sediments. Those metals have higher affinity with fine particles than with coarse ones, so that while the coarsest fraction from sediment plumes settled first, the finest fraction remained in suspension thus increasing the metals/sediments concentration ratio. On the other hand, Cd and Zn concentrations in suspended particles did not change significantly over time, which is thought to be caused by the fast dissolution of such metals in seawater. Beyond waste dumping itself, the observed increase in some metals in marine particulate material could have a significant impact on the adjacent coastal ecosystems due to their toxicity above certain thresholds. The consequences of the resuspension experiment here presented can be extrapolated to the impact of seafloor mining activities leading to the resuspension of metal-rich particle plumes into the water column. The experimental set-up presented here may be further explored for investigating metal behaviour during seafloor mining activities. [ABSTRACT FROM AUTHOR]