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Abstract: Condition indices and metal bioaccumulation of early life stages of juvenile flounder (5–10cm) were determined in three anthropogenic estuaries (the Scheldt, Seine and Loire) and compared to a reference site (the Canche). Significant correlations were found between metal concentrations in sediment and (i) fish liver for Cd, Cu, Ni, Pb, V and Zn and (ii) fish gills for Cd and Mn. Metal accumulation in juvenile flounder from the three anthropogenic estuaries coincided with significantly lower Fulton’s K indices (from 0.99±0.03 to 1.06±0.01mgmm−3) compared to those from the Canche estuary (from 1.02±0.01 to 1.13±0.01mgmm−3). This discrepancy in fish condition index increased with fish size and therefore, strongly depends on the time juvenile spend in estuary. Muscle lipid contents and Triacylglycerol to Sterol ratios were significantly lower in fish collected in the Scheldt (lipid content: 21.3±3.6%), Seine (17.9±19.8%) and Loire (19.5±2.4%) estuaries compared to those originating from the Canche (38.3±4.6%). This study highlights that combined measures of both fish metal contents and condition indices gives a relevant assessment of juvenile fish health growing in anthropogenic estuaries. [Copyright &y& Elsevier]

Abstract: Heterotrophic bacterial standing stocks (total and viable cells) and production were determined in the coastal surface waters of the eastern English Channel, during different stages of a phytoplankton succession. Two coastal zones of variable freshwater influence were surveyed within the ‘coastal flow system’ (Wimereux and Somme Bay) where massive and recurrent Phaeocystis globosa blooms take place in spring. The proportion of intact (MEM+) cells, assessed by the LIVE/DEAD® BacLight™ (L/D) method, varied from 15 to 94% at the two coastal stations studied (median of 46%). MEM+ and total (DAPI) cell counts were significantly correlated over the study period, whereas the higher proportion of MEM+ cells did not correspond to an elevated bacterial cell production (BP). Low levels of living (potentially active) cells were nevertheless responsible for the high productivity levels within the bacterial community when the P. globosa bloom declined. Our study revealed that the bacterial carbon production/primary production ratios (BCP/PP) showed broad variations (7 to 111%) within each site, going from low values (7–16%) when the bloom was the most productive, to higher values (61–111%) at the end of the bloom. This suggested (i) a temporal uncoupling between bacteria and phytoplankton throughout the bloom duration and (ii) a drastic change of the amount of PP potentially processed by the bacterial community among high and low productive periods. The BCP increase after the decline of the P. globosa bloom implies that, at this time, a large part of the phytoplankton-derived organic matter (OM) was remineralised via the bacterial heterotrophic production. With respect to the L/D results, this bacterial remineralisation was due to a small yet productive total cell fraction. [Copyright &y& Elsevier]

Estuaries are considered one of the most dynamic ecosystems in the world, ensuring high production and transfer of large quantities of organic matter (OM) from continents to the ocean. Despite the large influence of estuaries in the functioning of coastal ecosystems, our understanding of OM dynamics in these buffering coastal environments remains fragmented. In this frame, our study was carried out to describe and understand the main drivers of OM distribution in two estuaries (Canche, Authie) of the eastern English Channel, based on descriptive and quantitative approaches. For this purpose, in February and March 2018, surface sediments were sampled at low tide along cross-shore transects in the intertidal zone of each estuary. Analysis of sediment grain size, porosity, proportion of aggregated particles, total carbonate content and organic geochemical characteristics (total OM content, atomic TOC/TN ratio, δ13C value) of surface sediments allowed identifying four biosedimentary facies: sand flat, mud flat, low and high salt marshes. In parallel, the elemental and isotopic characterization of the suspended particulate OM inputs by the rivers, the surface biofilms and the halophytic vegetation was performed to trace the three major sources contributing to sedimentary OM in both estuaries. Spatial distribution of OM in surface sediments (ranging between 0.6 and 26.9% dry weight) evidenced higher contents along marsh platforms than in sand and mud flats. and the OM pool was mainly constituted of a mixing of C 3 terrestrial vascular plants, marine and riverine phytoplankton. The comparison between both estuaries highlighted that the geomorphology impacted by natural and anthropic factors plays a preponderant role in the distribution and the sources of sedimentary OM by influencing vegetation communities and hydrodynamic processes. In the context of sea level rise, an improved understanding of the OM dynamics within each biosedimentary facies is crucial to better constrain and assess the role of macrotidal estuaries in carbon cycle. • Field observation and physico-chemical analyses of exhaustive surface sediment samples used for determining biosedimentary facies. • Source of sedimentary organic matter defined by elemental and isotopic proxies. • Influence of the structure and texture of surface sediments on OM distribution. • Principal Components Analysis highlighted two contrasted geomorphological stages. [ABSTRACT FROM AUTHOR]