Abstract

One of the factors affecting the dynamics of the coastal marine ecosystem off central-southern Chile is the presence (up to ~325 km alongshore) of a low-salinity plume caused by the main rivers in the region. Although the influence of this plume on oceanographic variables have been widely documented, the same is not true of its microbiological impact. We studied changes in the community structure of free-living prokaryotes (bacteria plus archaea) along a marine-freshwater transect in central-southern Chile using PCR-DGGE. Three continental freshwater systems were sampled in 2007 during the high-flow period (winter and early spring), and the coastal area was sampled in winter and summer. Our results revealed a few phylotypes widely distributed from rivers to the sea and important differences between these habitats. The level of similarity between DGGE banding patterns from freshwater and marine stations ranged from 0 to 32%; the number of prokaryote OTUs in the freshwater systems was normally higher for the estuarine zones. Our statistical analysis identified season of the year and/or depth as the variables that had a statistically significant effect (p<0.05) on the number of prokaryote OTUs in the coastal area. Moreover, we found two different communities of bacteria and archaea inhabiting different strata of the coastal water column. Our results indicated a clear differentiation of the ecological niches for free-living prokaryotic communities in continental freshwater systems and the coastal environment. This differentiation prevented marine-freshwater transitions in prokaryotes which stimulated the development of native communities in estuarine zones. © Springer-Verlag and the University of Milan 2011.