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Environmental Variables Influence on Spatial Distribution of Bacterial Communities Across the English Channel in Two
Luen-Luen Li1, Nicolas Delatre1, Zéline Hubert1
1Université du Littoral Côte d'Opale, CNRS, Univ. Lille, UMR 8187, LOG, Laboratoire d'Océanologie et de Géosciences, Wimereux, France.
Environmental Microbiology Reports
|October 12, 2025
Summary
Seasonal changes in the English Channel reveal distinct bacterial communities. Spring communities are linked to nutrients and particulate matter, while summer communities correlate with salinity, showing coastal-offshore gradients.
Area of Science:
- Marine Ecology
- Microbial Ecology
- Oceanography
Background:
- The English Channel's diverse habitats support rich biodiversity.
- These ecosystems face natural and anthropogenic pressures.
- Understanding pelagic bacterial communities is crucial for ecosystem health.
Purpose of the Study:
- To analyze environmental variables and bacterial communities in French English Channel and North Sea waters.
- To investigate seasonal variations in pelagic bacterial diversity and structure.
- To determine the influence of environmental factors on bacterial community composition.
Main Methods:
- Oceanographic sampling during 'EcoPel' campaigns (spring and summer 2018).
- Analysis of environmental variables including suspended particulate matter (SPM), particulate organic matter (POM), particulate inorganic matter (PIM), salinity, nutrients, and chlorophyll-a (Chl-a).
- Principal Component Analysis (PCA), Shannon diversity index, hierarchical cluster analysis, and distance correlation for bacterial community analysis.
Main Results:
- Environmental variables differed between spring (SPM, POM, PIM, salinity, NO2-/NO3+) and summer (salinity, SPM, Si, Chl-a).
- Bacterial alpha diversity (richness and equitability) was higher in summer than in spring.
- Bacterial community structure showed clear seasonality: spring communities were dominated by Bacteroidetes, while summer communities featured more Proteobacteria, Actinobacteria, Verrucomicrobia, and Planctomycetes.
- Spring bacterial composition correlated with Chl-a, PO4, POM, SPM, and PIM; summer composition correlated with salinity.
- Both environmental variables and bacterial communities exhibited coastal-offshore clustering, indicating influence from coastal gradients, river inputs, and phytoplankton dynamics.
Conclusions:
- Significant seasonal shifts occur in English Channel pelagic bacterial communities.
- Environmental factors, particularly nutrients and particulate matter in spring and salinity in summer, drive these seasonal changes.
- Coastal-offshore gradients play a major role in structuring pelagic bacterial communities in this region.
