| Popis: |
Estuaries are among the most productive ecosystems in the world and are highly dynamic due to the interaction of freshwater and seawater, which results in strong spatial gradients in physico-chemical conditions. Bacterioplankton play a central role in these systems, driving the fluxes of carbon and energy, and being central for contaminant removal in human-impacted areas. Most studies on bacterioplankton dynamics have been carried out in temperate estuaries, and they show that salinity is a major factor driving bacterioplankton distribution. Tropical estuaries, although largely understudied, experience drastic variations in river discharge between the dry and the rainy seasons, influencing the spatial distribution of the salinity gradient and thus likely impacting bacterioplankton communities. Using Illumina sequencing of the 16S rRNA gene, here we studied bacterial communities from the Nicoya’s gulf (Costa Rica), a large tropical estuary characterized by high riverine discharge during the rainy season, to explore seasonal changes in the spatial distribution and connectivity of these communities along the Gulf. Our results show pronounced differences in bacterial diversity and community structure between seasons and zones within the estuary (the shallow upper Gulf, the middle zone and the lower zone, located in the marine end of the estuary). Various Enterobacteriales genera and Cyanobacteria dominated the bacterial communities in the dry season, whereas Alphaproteobacteria dominated the communities in the rainy season. These seasonal patterns were similar to the seasonal variations observed in bacterial assemblages during almost a year within a single station in the upper region of the Gulf. We conclude that the Gulf is highly dynamic in both the spatial and temporal scale and that bacterioplankton communities are strongly influenced by the riverine and tidal inputs during both seasons. |
