This study examines the seasonal dynamics of microbial communities in the Western English Channel over a 6-year period using high-resolution 16S rRNA tag pyrosequencing. The analysis identified 8,794 operational taxonomic units (OTUs) and 21,130 OTUs after denoising, with *Alphaproteobacteria* being the most abundant class. Seasonal patterns were observed, particularly in winter, with strong repeatable cycles in community diversity. Environmental variables, such as day length, explained more variation in seasonally predictable bacteria than protists or metazoan biomass. The study found that changes in day length alone explained over 65% of the variance in community diversity, suggesting that environmental factors are more influential than trophic interactions. Microbial association network analysis revealed stronger correlations within bacterial taxa compared to interactions between bacteria and eukaryotes, or between bacteria and environmental variables. The results highlight the importance of environmental factors in shaping microbial community structure and dynamics in temperate marine environments.This study examines the seasonal dynamics of microbial communities in the Western English Channel over a 6-year period using high-resolution 16S rRNA tag pyrosequencing. The analysis identified 8,794 operational taxonomic units (OTUs) and 21,130 OTUs after denoising, with *Alphaproteobacteria* being the most abundant class. Seasonal patterns were observed, particularly in winter, with strong repeatable cycles in community diversity. Environmental variables, such as day length, explained more variation in seasonally predictable bacteria than protists or metazoan biomass. The study found that changes in day length alone explained over 65% of the variance in community diversity, suggesting that environmental factors are more influential than trophic interactions. Microbial association network analysis revealed stronger correlations within bacterial taxa compared to interactions between bacteria and eukaryotes, or between bacteria and environmental variables. The results highlight the importance of environmental factors in shaping microbial community structure and dynamics in temperate marine environments.