Abstract
Over the past century the spread of hypoxia in the Baltic Sea has been drastic, reaching its ‘arm’ into the easternmost sub-basin, the Gulf of Finland. The hydrographic and climatological properties of the gulf offer a broad suite of discrete niches for microbial communities. The current study explores spatiotemporal dynamics of bacterioplankton community in the Gulf of Finland using massively parallel sequencing of 16S rRNA fragments obtained by amplifying community DNA from spring to autumn period. The presence of redoxcline and drastic seasonal changes make spatiotemporal dynamics of bacterioplankton community composition (BCC) and abundances in such estuary remarkably complex. To the best of our knowledge, this is the first study that analyses spatiotemporal dynamics of BCC in relation to phytoplankton bloom throughout the water column (and redoxcline), not only at the surface layer. We conclude that capability to survive (or benefit from) shifts between oxic and hypoxic conditions is vital adaptation for bacteria to thrive in such environments. Our results contribute to the understanding of emerging patterns in BCCs that occupy hydrographically similar estuaries dispersed all over the world, and we suggest the presence of a global redox- and salinity-driven metacommunity. These results have important implications for understanding long-term ecological and biogeochemical impacts of hypoxia expansion in the Baltic Sea (and similar ecosystems), as well as global biogeography of bacteria specialized inhabiting similar ecosystems.
Highlights
Two of the most significant issues facing coastal zone management are habitat loss and alteration due to anthropogenic pollution fuelled by eutrophication, which in the case of the Baltic Sea is amended with vicious positive feedback loop caused by oxygen depletion leading to increased phosphate release from sediments [1]
Our results and previous investigations of bacterioplankton community composition (BCC) of the Baltic Sea [12, 15,16,17, 22, 24] reflect the presence of the ‘rare biosphere’, which is represented by the long tail pattern found in rank-abundance curves of bacterial species [46,47,48]
The present study provided a detailed insight into spatiotemporal patterns of BCC in the Gulf of Finland, a stratified estuary suffering from oxygen depletion in the near bottom layer
Summary
Two of the most significant issues facing coastal zone management are habitat loss and alteration due to anthropogenic pollution fuelled by eutrophication, which in the case of the Baltic Sea is amended with vicious positive feedback loop caused by oxygen depletion leading to increased phosphate release from sediments [1]. Spatiotemporal studies of variability of bacterioplankton community composition (BCC) in coastal margins have shown that the spatial variability can extend over seasonal changes, given a sharp gradient of environmental factor (e.g. salinity, oxygen) [6, 7]. A recent study of spatiotemporal dynamics of artificially oxygenated fjord (Byfjord, Sweden) that has comparable trophic conditions with the Baltic Sea demonstrated that the amount of oxygen available shaped the bacterial communities, regardless of the depths or the season they were collected in [7]
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