The impact of the seasonal deposition of phytoplankton and phytodetritus on surface sediment bacterial abundance and community composition was investigated at the Western English Channel site L4. Sediment and water samples were collected from January to September in 2012, increasing in frequency during periods of high water column phytoplankton abundance. Compared to the past two decades, the spring bloom in 2012 was both unusually long in duration and contained higher than average biomass. Within spring months, the phytoplankton bloom was well mixed through the water column and showed accumulations near the sea bed, as evidenced by flow cytometry measurements of nanoeukaryotes, water column chlorophyll and the appearance of pelagic phytoplankton at the sediment. Measurements of chlorophyll and chlorophyll degradation products indicated phytoplankton material was heavily degraded only when it reached the sediment surface: the nature of the chlorophyll degradation products was indicative of grazing activity. The abundance of bacterial 16S rRNA genes per gram sediment (used as a proxy for bacterial biomass) increased markedly with the onset of the phytoplankton bloom, and correlated with measurements of chlorophyll at the sediment surface. Together, this suggests that bacteria may have responded to nutrients released via grazing activity. In depth sequencing of 16S rRNA genes was also performed on four replicate samples from eight sampling point throughout the duration of the spring bloom. This indicated that the composition of the bacterial community shifted rapidly through-out the prolonged spring bloom period; primarily due to an increase in the abundance of members of the Flavobacteria.