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Microbe biogeography tracks water masses in a dynamic oceanic frontal system
Anni Djurhuus1, Philipp H Boersch-Supan2, Svein-Ole Mikalsen3
1Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK; College of Marine Science, University of South Florida, 830 1st St SE, St Petersburg, FL 33701, USA.
Royal Society Open Science
|April 14, 2017
Summary
Microbial communities in the ocean are shaped by both depth and water masses, not just distance. This study reveals distinct microbial biogeography patterns linked to oceanographic fronts and water types in the southwest Indian Ocean.
Area of Science:
- Marine microbiology
- Biogeography
- Oceanography
Background:
- Dispersal limitation significantly influences microbial biogeography, contrary to expectations of weak distance-decay in high-dispersal pelagic environments.
- Previous studies indicate limited regional-scale (100 km) geographical heterogeneity in microbial communities.
- Ocean currents in pelagic zones are presumed to facilitate widespread microbial dispersal.
Purpose of the Study:
- To investigate the spatial structure of microbial communities across dynamic frontal zones in the southwest Indian Ocean.
- To understand the influence of different water masses and depth layers on microbial biogeography.
- To assess microbial operational taxonomic unit (OTU) diversity and abundance across latitudinal and depth gradients.
Main Methods:
- Collection of 153 free-living microorganism samples from five seamounts along a subtropical to subantarctic gradient.
- Sampling across three distinct depth layers: sub-surface chlorophyll maximum (~40 m), euphotic zone bottom (~200 m), and benthic boundary layer (300-2000 m).
- Assessment of microbial diversity and abundance using 16S rRNA gene amplification and sequencing on an Illumina MiSeq platform, followed by multivariate analyses.
Main Results:
- Microbial communities were structured more strongly by depth than by latitude, with consistent phyla across depth strata on seamounts.
- The deep layer (Antarctic intermediate water) showed homogeneity across the survey area.
- OTU turnover was observed across fronts in the sub-surface and intermediate depth layers, indicating three distinct biological regimes (subantarctic surface water, convergence zone, subtropical).
Conclusions:
- Microbial biogeography across depth and latitudinal gradients is strongly linked to the water masses microbes inhabit.
- Regional patterns of microbial biogeography correspond to the physical oceanography of the southwest Indian Ocean.
- Depth and water mass characteristics are key drivers of microbial community structure in this dynamic frontal zone.