title: Spatio-Temporal Interdependence of Bacteria and Phytoplankton during a Baltic Sea Spring Bloom.
abstract: In temperate systems, phytoplankton spring blooms deplete inorganic nutrients and are major sources of organic matter for the microbial loop. In response to phytoplankton exudates and environmental factors, heterotrophic microbial communities are highly dynamic and change their abundance and composition both on spatial and temporal scales. Yet, most of our understanding about these processes comes from laboratory model organism studies, mesocosm experiments or single temporal transects. Spatial-temporal studies examining interactions of phytoplankton blooms and bacterioplankton community composition and function, though being highly informative, are scarce. In this study, pelagic microbial community dynamics (bacteria and phytoplankton) and environmental variables were monitored during a spring bloom across the Baltic Proper (two cruises between North Germany to Gulf of Finland). To test to what extent bacterioplankton community composition relates to the spring bloom, we used next generation amplicon sequencing of the 16S rRNA gene, phytoplankton diversity analysis based on microscopy counts and population genotyping of the dominating diatom Skeletonema marinoi. Several phytoplankton bloom related and environmental variables were identified to influence bacterial community composition. Members of Bacteroidetes and Alphaproteobacteria dominated the bacterial community composition but the bacterial groups showed no apparent correlation with direct bloom related variables. The less abundant bacterial phyla Actinobacteria, Planctomycetes, and Verrucomicrobia, on the other hand, were strongly associated with phytoplankton biomass, diatom:dinoflagellate ratio, and colored dissolved organic matter (cDOM). Many bacterial operational taxonomic units (OTUs) showed high niche specificities. For example, particular Bacteroidetes OTUs were associated with two distinct genetic clusters of S. marinoi. Our study revealed the complexity of interactions of bacterial taxa with inter- and intraspecific genetic variation in phytoplankton. Overall, our findings imply that biotic and abiotic factors during spring bloom influence bacterial community dynamics in a hierarchical manner.
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems - EEMiS, Linnaeus University Kalmar, Sweden.
authors.forename: Carina
authors.initials: C
authors.lastname: Bunse
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems - EEMiS, Linnaeus University Kalmar, Sweden.
authors.forename: Mireia
authors.initials: M
authors.lastname: Bertos-Fortis
authors.affiliation: Aquatic Ecology, Lund University Lund, Sweden.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Sassenhagen
authors.affiliation: Marine Systems Institute, Tallinn University of Technology Tallinn, Estonia.
authors.forename: Sirje
authors.initials: S
authors.lastname: Sildever
authors.affiliation: Finnish Environmental Institute/Marine Research CentreHelsinki, Finland; Environmental and Marine Biology, Åbo Akademi UniversityÅbo, Finland.
authors.forename: Conny
authors.initials: C
authors.lastname: Sjöqvist
authors.affiliation: Department of Marine Sciences, University of Gothenburg Gothenburg, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Godhe
authors.affiliation: Department of Marine Sciences, University of Gothenburg Gothenburg, Sweden.
authors.forename: Susanna
authors.initials: S
authors.lastname: Gross
authors.affiliation: Finnish Environmental Institute/Marine Research Centre Helsinki, Finland.
authors.forename: Anke
authors.initials: A
authors.lastname: Kremp
authors.affiliation: Marine Systems Institute, Tallinn University of Technology Tallinn, Estonia.
authors.forename: Inga
authors.initials: I
authors.lastname: Lips
authors.affiliation: Natural History Museum of Denmark, University of Copenhagen Copenhagen, Denmark.
authors.forename: Nina
authors.initials: N
authors.lastname: Lundholm
authors.affiliation: Aquatic Ecology, Lund University Lund, Sweden.
authors.forename: Karin
authors.initials: K
authors.lastname: Rengefors
authors.affiliation: Department of Marine Sciences, University of Gothenburg Gothenburg, Sweden.
authors.forename: Josefin
authors.initials: J
authors.lastname: Sefbom
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems - EEMiS, Linnaeus University Kalmar, Sweden.
authors.forename: Jarone
authors.initials: J
authors.lastname: Pinhassi
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems - EEMiS, Linnaeus University Kalmar, Sweden.
authors.forename: Catherine
authors.initials: C
authors.lastname: Legrand
keywords: 16S rRNA; Baltic Sea; Skeletonema marinoi; bacterioplankton; marine bacteria; phytoplankton; spatio-temporal; spring bloom