Resilience and adjustments of surface sediment bacterial communities in an enclosed shallow coastal lagoon, Magdalen Islands, Gulf of St. Lawrence, Canada

Bacteria regulate global biogeochemical cycles and much of this activity occurs in shallow coastal sediments; however, little is known of the seasonality or how changes in environmental conditions influence the active sediment bacterial communities. Havre-aux-Maisons (Magdalen Islands, Canada), a relatively pristine enclosed shallow coastal lagoon, is of particular biological interest since it has no inflowing rivers and provides an opportunity to investigate non-estuarine shallow marine sediments. Potentially active taxa in surface sediments were identified over a 15-month period using high-throughput rRNA amplicon sequencing. Sediment bacterial communities were diverse at the species level, with high Beta diversity. Throughout most of the sampling period, communities consisted of taxa that were closely related to each other, suggesting that specific environmental conditions at a given time point favored taxa with similar ecological traits. However, bacterial phyla and proteobacterial classes were remarkably similar over time with a predominantly sulfur cycling community composed of sulfur-oxidizing Gammaproteobacteria and sulfate-reducing Deltaproteobacteria persisting over much of the sampling period, despite the oxygenated water column. This community was disrupted after a storm and less common phyla became relatively more abundant. Following this disruption, a high proportion of benthic Cyanobacteria colonized the sediment before the reestablishment of the sulfur-cycle-dominated community.