Environmental Variables Influence on Spatial Distribution of Bacterial Communities Across the English Channel in Two...

The English Channel features a wide range of ecological habitats that host numerous biodiversity resources and are submitted to natural and/or anthropogenic pressures. During the 'EcoPel' oceanographic campaigns (spring and summer 2018) in French waters of the English Channel and North Sea, a variety of coastal pelagic habitats were sampled for analysing environmental variables and bacterial communities. Results of PCA suggest that main environmental variables were SPM, POM, PIM, salinity and NO₂ ^-/NO₃ ⁺ in spring and salinity, SPM, Si and Chl-a in summer. The Shannon index suggested summer alpha diversity had higher richness and equitability compared to spring. A clear seasonality in the bacterial community structure was also revealed by hierarchical cluster analysis. Most of the spring communities had a higher proportion of Bacteroidetes while most of the summer communities had a higher proportion of Proteobacteria, Actinobacteria, Verrucomicrobia and Planctomycetes. Based on distance correlations and statistical significance, the spring taxonomic composition was correlated with Chl-a, PO₄, POM, SPM and PIM, while the summer composition was correlated with salinity. According to hierarchical cluster analyses, both environmental variables and bacterial communities seem to be clustered in parallel with the coast, evidencing the main influence of coastal-offshore gradients and implying possible links with river inputs and phytoplankton/algae dynamics.