title: A light-induced shortcut in the planktonic microbial loop.
abstract: Mixotrophs combine photosynthesis with phagotrophy to cover their demands in energy and essential nutrients. This gives them a competitive advantage under oligotropihc conditions, where nutrients and bacteria concentrations are low. As the advantage for the mixotroph depends on light, the competition between mixo- and heterotrophic bacterivores should be regulated by light. To test this hypothesis, we incubated natural plankton from the ultra-oligotrophic Eastern Mediterranean in a set of mesocosms maintained at 4 light levels spanning a 10-fold light gradient. Picoplankton (heterotrophic bacteria (HB), pico-sized cyanobacteria, and small-sized flagellates) showed the fastest and most marked response to light, with pronounced predator-prey cycles, in the high-light treatments. Albeit cell specific activity of heterotrophic bacteria was constant across the light gradient, bacterial abundances exhibited an inverse relationship with light. This pattern was explained by light-induced top-down control of HB by bacterivorous phototrophic eukaryotes (PE), which was evidenced by a significant inverse relationship between HB net growth rate and PE abundances. Our results show that light mediates the impact of mixotrophic bacterivores. As mixo- and heterotrophs differ in the way they remineralize nutrients, these results have far-reaching implications for how nutrient cycling is affected by light.
authors.affiliation: ICBM, University of Oldenburg, Schleusenstrasse 1, DE-26382 Wilhelmshaven, Oldenburg, Germany.|WasserCluster Lunz - Biologische Station GmbH, Dr Carl Kupelwieser Promenade 5, A-3293 Lunz am See, Austria.
authors.forename: Robert
authors.initials: R
authors.lastname: Ptacnik
authors.affiliation: Institut de Ciències del Mar, CSIC, Pg Marítim de la Barceloneta, 37-49, 08003 Barcelona, Catalunya, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Gomes
authors.affiliation: Institut de Ciències del Mar, CSIC, Pg Marítim de la Barceloneta, 37-49, 08003 Barcelona, Catalunya, Spain.
authors.forename: Sarah-Jeanne
authors.initials: SJ
authors.lastname: Royer
authors.affiliation: Department of Biology, University of Bergen, P.O. Box 7803, 5020 Bergen, Norway.|Leibniz Institute of Freshwater Ecology and Inland Fisheries, Dep. 3, Experimental Limnology, Alte Fischerhütte 2, 16775 Stechlin, Germany.
authors.forename: Stella A
authors.initials: SA
authors.lastname: Berger
authors.affiliation: Institut de Ciències del Mar, CSIC, Pg Marítim de la Barceloneta, 37-49, 08003 Barcelona, Catalunya, Spain.
authors.forename: Albert
authors.initials: A
authors.lastname: Calbet
authors.affiliation: Department of Biology, University of Bergen, P.O. Box 7803, 5020 Bergen, Norway.|Leibniz Institute of Freshwater Ecology and Inland Fisheries, Dep. 3, Experimental Limnology, Alte Fischerhütte 2, 16775 Stechlin, Germany.
authors.forename: Jens C
authors.initials: JC
authors.lastname: Nejstgaard
authors.affiliation: Institut de Ciències del Mar, CSIC, Pg Marítim de la Barceloneta, 37-49, 08003 Barcelona, Catalunya, Spain.
authors.forename: Josep M
authors.initials: JM
authors.lastname: Gasol
authors.affiliation: Institut de Ciències del Mar, CSIC, Pg Marítim de la Barceloneta, 37-49, 08003 Barcelona, Catalunya, Spain.|Red Sea Research Center, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology, 23955-6900 Thuwal, Kingdom of Saudi Arabia.
authors.forename: Stamatina
authors.initials: S
authors.lastname: Isari
authors.affiliation: ICBM, University of Oldenburg, Schleusenstrasse 1, DE-26382 Wilhelmshaven, Oldenburg, Germany.
authors.forename: Stefanie D
authors.initials: SD
authors.lastname: Moorthi
authors.affiliation: ICBM, University of Oldenburg, Schleusenstrasse 1, DE-26382 Wilhelmshaven, Oldenburg, Germany.|WasserCluster Lunz - Biologische Station GmbH, Dr Carl Kupelwieser Promenade 5, A-3293 Lunz am See, Austria.
authors.forename: Radka
authors.initials: R
authors.lastname: Ptacnikova
authors.affiliation: ICBM, University of Oldenburg, Schleusenstrasse 1, DE-26382 Wilhelmshaven, Oldenburg, Germany.|European Institute for Marine Studies, Technopole Brest-Iroise, Plouzane, France.
authors.forename: Maren
authors.initials: M
authors.lastname: Striebel
authors.affiliation: P.P. Shirshov Institute of Oceanology RAS, 36 Nahimovski prospect, 117997 Moscow, Russia.
authors.forename: Andrey F
authors.initials: AF
authors.lastname: Sazhin
authors.affiliation: Department of Biology, University of Bergen, P.O. Box 7803, 5020 Bergen, Norway.|Institute of Oceanography, Hellenic Centre for Marine Research, P.O. Box 2214, 71003 Heraklion, Crete, Greece.|Department of Biology, University of Crete, Voutes University Campus, 70013 Heraklion, Crete, Greece.
authors.forename: Tatiana M
authors.initials: TM
authors.lastname: Tsagaraki
authors.affiliation: Institute of Oceanography, Hellenic Centre for Marine Research, P.O. Box 712, 19013 Anavyssos, Greece.
authors.forename: Soultana
authors.initials: S
authors.lastname: Zervoudaki
authors.affiliation: Marine Systems Institute at Tallinn University of Technology, Akadeemia Rd. 15A, 12618 Tallinn, Estonia.
authors.forename: Kristi
authors.initials: K
authors.lastname: Altoja
authors.affiliation: Department of Biology, University of Crete, Voutes University Campus, 70013 Heraklion, Crete, Greece.
authors.forename: Panagiotis D
authors.initials: PD
authors.lastname: Dimitriou
authors.affiliation: Marine Systems Institute at Tallinn University of Technology, Akadeemia Rd. 15A, 12618 Tallinn, Estonia.
authors.forename: Peeter
authors.initials: P
authors.lastname: Laas
authors.affiliation: Middle East Technical University, Institute of Marine Sciences, P.O. Box 28, 33731, Erdemli, Mersin, Turkey.
authors.forename: Ayse
authors.initials: A
authors.lastname: Gazihan
authors.affiliation: Institut de Ciències del Mar, CSIC, Pg Marítim de la Barceloneta, 37-49, 08003 Barcelona, Catalunya, Spain.
authors.forename: Rodrigo A
authors.initials: RA
authors.lastname: Martínez
authors.affiliation: WasserCluster Lunz - Biologische Station GmbH, Dr Carl Kupelwieser Promenade 5, A-3293 Lunz am See, Austria.|Department of Limnology, University of Vienna, Althanstrasse 14, 1090, Vienna, AT.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Schabhüttl
authors.affiliation: Department of Biology, University of Crete, Voutes University Campus, 70013 Heraklion, Crete, Greece.
authors.forename: Ioulia
authors.initials: I
authors.lastname: Santi
authors.affiliation: Department of Biology, University of Crete, Voutes University Campus, 70013 Heraklion, Crete, Greece.
authors.forename: Despoina
authors.initials: D
authors.lastname: Sousoni
authors.affiliation: Institute of Oceanography, Hellenic Centre for Marine Research, P.O. Box 2214, 71003 Heraklion, Crete, Greece.
authors.forename: Paraskevi
authors.initials: P
authors.lastname: Pitta
mesh_terms: D000818:Animals; D052818:Autotrophic Processes; D018533:Biomass; D017753:Ecosystem; D052836:Heterotrophic Processes; D008027:Light; D008522:Mediterranean Sea; D009928:Organ Specificity; D010788:Photosynthesis; D010933:Plankton / Q000502:physiology*; D011235:Predatory Behavior