| description |
Bacterioplankton communities of the dark ocean are distinct for the oceanographic water masses, which are transported over thousands of kilometers, and they are additionally shaped by water depth. Here we studied the role of those parameters on bacterioplankton community structure along a transect (31°S - 39°N, sampling depths between 350 m and 4,300 m) crossing the mid-Atlantic ridge at the equator, which enabled us to investigate its role as a potential barrier to dispersal. Illumina sequencing of the V5-6 hypervariable region of the 16S rRNA gene was used for community analysis. PERMANOVA test showed that water mass accounted for 24% of the observed variation, followed by ocean basin (northern or southern hemisphere) and pelagic zone which explained roughly 13% of the total variation each. PCO analysis and hierarchal clustering clearly separated samples according to water mass and pelagic zone; additionally, abyssal samples from the northern and southern Atlantic Ocean clustered separately. A significant distance-decay relationship was observed for the abyssal samples but not for those from the mesopelagic zone. Large differences in the relative abundances of phyla and OTUs were found in the pelagic realms as well as when comparing northern and southern ocean basins, about 20% of all OTUs were endemic for one pelagic realm, and 23% for one ocean basin. Our analysis revealed that deep ocean bacterioplankton communities are shaped by the concomitant action of three forces: selection driven by depth, dispersal through transport within water masses, and dispersal limitation due to submarine mountains. The data suggest that the abyssopelagic zone of the dark ocean consists of geographically isolated sub-basins in which allopatric speciation may occur. |