AME 66:33-40 (2012)  -  DOI: https://doi.org/10.3354/ame01550

ABSTRACT: Bacterioplankton assemblages play crucial ecosystem roles in diverse aquatic habitats. Areas in which 2 distinct aquatic bodies converge provide insight into how bacterial communities respond to dramatic environmental change and assemblage confluence. The tolerance and success of combined assemblage components to mixed conditions, however, is unclear. To address this, freshwater (FW) and seawater (SW) were combined in ratios of entirely SW, 1:10, 1:1, 10:1 and entirely FW in experimental mesocosms on Appledore Island, Gulf of Maine (Shoals Marine Laboratory), to examine the response of microbial abundance and composition to habitat convergence. The relative proportion of operational taxonomic units (OTUs) that increased in each incubation demonstrated that SW OTUs were more capable of success in FW habitats than FW OTUs in SW habitats. Most OTUs from each source that grew under confluent conditions were initially rare (<1% of the total fingerprint amplified fluorescence) in the incubations. These data demonstrate that rarer OTUs may be more responsive to environmental change than abundant OTUs. These data ultimately indicate that habitat confluence imparts changes in microbial assemblages and that mixing zones within areas of habitat confluence (e.g. estuaries and intertidal rock pools) select for new assemblages composed of OTUs that may be adapted to mixed conditions and that are at low abundance in source populations.

KEY WORDS: Microbial community · Mixing · Dispersal · Marine · Operational taxonomic unit · ARISA · Gulf of Maine