Oceanic fronts: transition zones for bacterioplankton community composition

Oceanic fronts are widespread mesoscale features that exist in the boundary between different water masses. Bacterioplankton (including Bacteria and Archaea) drive oceanic biogeochemical cycles, regulating the composition of Earth’s atmosphere and influencing climate. Despite the recognized importance of bacterioplankton on the marine biogeochemical cycles and the ubiquitousness of fronts, the effect of frontal zones on the distribution of bacterioplankton community remains unknown. Using 16S rRNA gene sequencing coupled with a high spatial resolution analysis of the physical properties of the water masses, we demonstrate strong shifts in bacterioplankton community composition (BCC) across the Subtropical Frontal Zone off New Zealand. Transition between water masses resulted in a clear modification of the dominant taxa and a significant increase in community dissimilarity. Our results, linking physical oceanography and marine molecular ecology, support the strong role of oceanic frontal zones in delimiting the distribution of bacterioplankton in the ocean, where fronts serve as clear transition zones, indicating boundaries for bacterioplankton distribution in the ocean. Owing to the widespread abundance of fronts in the marine environment, future efforts should focus on confirming their roles in demarking bacterioplankton distribution and whether they act as indicators of ecosystem process changes. This would allow a better understanding of the forces that control energy flow in the ocean as well as the cycling of compounds that influence climate change, and concomitantly building more accurate models of global biogeochemical cycles.