Aquatic bacterial assemblage variability in the supra littoral zone of Appledore Island, Gulf of Maine.
We investigated the abundance and assemblage variability of bacteria in 10 spatially distinct freshwater pools on Appledore Island, Gulf of Maine. Assemblages were strongly heterogeneous between pools separated by even short distances. To gain insight into factors that may lead to the establishment of novel assemblages, we conducted an ecosystem-open choromophoric dissolved organic matter (CDOM) enrichment experiment within mesocosms inoculated with a standardized microbial community and observed patterns of their composition over time. Assemblages were strongly divergent from each other in composition after only 3 days of incubation. Divergence among mesocosms was significantly higher with increasing levels of CDOM. CDOM addition initially had a strong positive impact on bacterial operation taxonomic unit (OTU) richness and negative impact on bacterial OTU evenness, but no impact on total bacterial abundance, suggesting that factors controlling abundance are decoupled from those influencing overall composition.