title: More, smaller bacteria in response to ocean's warming?
abstract: Heterotrophic bacteria play a major role in organic matter cycling in the ocean. Although the high abundances and relatively fast growth rates of coastal surface bacterioplankton make them suitable sentinels of global change, past analyses have largely overlooked this functional group. Here, time series analysis of a decade of monthly observations in temperate Atlantic coastal waters revealed strong seasonal patterns in the abundance, size and biomass of the ubiquitous flow-cytometric groups of low (LNA) and high nucleic acid (HNA) content bacteria. Over this relatively short period, we also found that bacterioplankton cells were significantly smaller, a trend that is consistent with the hypothesized temperature-driven decrease in body size. Although decadal cell shrinking was observed for both groups, it was only LNA cells that were strongly coherent, with ecological theories linking temperature, abundance and individual size on both the seasonal and interannual scale. We explain this finding because, relative to their HNA counterparts, marine LNA bacteria are less diverse, dominated by members of the SAR11 clade. Temperature manipulation experiments in 2012 confirmed a direct effect of warming on bacterial size. Concurrent with rising temperatures in spring, significant decadal trends of increasing standing stocks (3% per year) accompanied by decreasing mean cell size (-1% per year) suggest a major shift in community structure, with a larger contribution of LNA bacteria to total biomass. The increasing prevalence of these typically oligotrophic taxa may severely impact marine food webs and carbon fluxes by an overall decrease in the efficiency of the biological pump.
authors.affiliation: Red Sea Research Center, Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Asturies 33212, Spain xelu.moran@kaust.edu.sa.
authors.forename: Xosé Anxelu G
authors.identifier: 0000-0002-9823-5339
authors.initials: XA
authors.lastname: Morán
authors.affiliation: Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Asturies 33212, Spain Marine Research Division, AZTI Tecnalia, Sukarrieta, Bizkaia 48395, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Alonso-Sáez
authors.affiliation: Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Asturies 33212, Spain.
authors.forename: Enrique
authors.identifier: 0000-0002-4222-928X
authors.initials: E
authors.lastname: Nogueira
authors.affiliation: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA.
authors.forename: Hugh W
authors.initials: HW
authors.lastname: Ducklow
authors.affiliation: Departamento de Biología y Geología, Física y Química Inorgánica, Universidad Rey Juan Carlos, Móstoles, Madrid 28933, Spain.
authors.forename: Natalia
authors.identifier: 0000-0003-0240-8221
authors.initials: N
authors.lastname: González
authors.affiliation: Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Asturies 33212, Spain.
authors.forename: Ángel
authors.initials: Á
authors.lastname: López-Urrutia
authors.affiliation: Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Asturies 33212, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Díaz-Pérez
authors.affiliation: Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Asturies 33212, Spain.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Calvo-Díaz
authors.affiliation: Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Asturies 33212, Spain.
authors.forename: Nestor
authors.initials: N
authors.lastname: Arandia-Gorostidi
authors.affiliation: Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Asturies 33212, Spain.
authors.forename: Tamara M
authors.identifier: 0000-0001-7331-8341
authors.initials: TM
authors.lastname: Huete-Stauffer
mesh_terms: D001267:Atlantic Ocean; D001419:Bacteria / Q000254:growth & development*; D057231:Climate Change; D057232:Global Warming; D064307:Microbiota; D010933:Plankton / Q000254:growth & development*; D012621:Seasons; D012623:Seawater / Q000382:microbiology*; D013030:Spain; D013696:Temperature
keywords: Atlantic Ocean; bacterioplankton; global warming; long-term trends; temperature–size relationships; time series