Spatial patterns of marine bacterioplankton along gradients of primary production in the Amundsen Sea Polynya, Southern Ocean

• During austral summers, the Southern Ocean's biota experience a sharp increase in primary production and a steepening of biotic and abiotic gradients, resulting from increased solar radiation and retreating ice.  In one of the largest ice-free patches - the Amundsen Sea Polynya - we aimed to identify connections between spatial diversity patterns of heterotrophic bacterioplankton and gradients of phytoplankton biomass. We gathered samples from throughout the depth profile at 15 sites during the austral summer of 2010/2011, collecting bacterioplankton and measuring several biotic and abiotic factors in the surrounding seawater.  We assessed bacterial community structure by targeting the 16S rRNA gene for pyrosequencing. Our overall goal was to identify patterns of spatial diversity in heterotrophic bacterioplankton and to generate and test mechanistic hypotheses for bacterioplankton community structure related to phytoplankton biomass, biotic and abiotic nutrients, and hydrological relationships due to depth and water mass.We found that processes acting within the photic surface related to the level of phytoplankton biomass induce a strong filtering effect by decreasing bacterioplankton community richness while increasing bacterioplankton abundance as phytoplankton biomass increases. We also found that the bacterioplankton community in the photic surface represents a subset of that found in the underlying dark water masses, likely reformed annually as the polynya appears; bacterial communities in surface waters reflect the communities found beneath, though as phytoplankton biomass increases, the similarity of these communities between different sites within the polynya increases, likely due to the filtering effect. The high phytoplankton biomass in the photic surface represents an important pool of organic matter and inorganic nutrients, fueling the underlying dark water with nutrients in a cascading effect; we found that in contrast to the community response in shallower water, the bacterioplankton community at the bottom of the phytoplankton biomass increased in diversity as phytoplankton biomass in overlying waters increased, while deeper waters remained largely unaffected. We propose that this lack of, response in deeper water masses gives rise to the observed high group dispersal in bacterial community composition in all water masses and the relatively homogenous community in the bottom water mass.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

marine bacterioplankton

community dynamics

Southern Ocean

Biologi med inriktning mot mikrobiologi

Biology with specialization in Microbiology

Publikations- och innehållstyp

vet (ämneskategori)

ovr (ämneskategori)