title: Microbial dinitrogen fixation in coral holobionts exposed to thermal stress and bleaching.
abstract: Coral holobionts (i.e., coral-algal-prokaryote symbioses) exhibit dissimilar thermal sensitivities that may determine which coral species will adapt to global warming. Nonetheless, studies simultaneously investigating the effects of warming on all holobiont members are lacking. Here we show that exposure to increased temperature affects key physiological traits of all members (herein: animal host, zooxanthellae and diazotrophs) of both Stylophora pistillata and Acropora hemprichii during and after thermal stress. S. pistillata experienced severe loss of zooxanthellae (i.e., bleaching) with no net photosynthesis at the end of the experiment. Conversely, A. hemprichii was more resilient to thermal stress. Exposure to increased temperature (+ 6°C) resulted in a drastic increase in daylight dinitrogen (N2 ) fixation, particularly in A. hemprichii (threefold compared with controls). After the temperature was reduced again to in situ levels, diazotrophs exhibited a reversed diel pattern of activity, with increased N2 fixation rates recorded only in the dark, particularly in bleached S. pistillata (twofold compared to controls). Concurrently, both animal hosts, but particularly bleached S. pistillata, reduced both organic matter release and heterotrophic feeding on picoplankton. Our findings indicate that physiological plasticity by coral-associated diazotrophs may play an important role in determining the response of coral holobionts to ocean warming.
authors.affiliation: Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, DE, 28359, Bremen, Germany.|Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, Research Network Chemistry meets Microbiology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Ulisse
authors.initials: U
authors.lastname: Cardini
authors.affiliation: Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, DE, 28359, Bremen, Germany.
authors.forename: Nanne
authors.initials: N
authors.lastname: van Hoytema
authors.affiliation: Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, DE, 28359, Bremen, Germany.
authors.forename: Vanessa N
authors.initials: VN
authors.lastname: Bednarz
authors.affiliation: Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, DE, 28359, Bremen, Germany.
authors.forename: Laura
authors.initials: L
authors.lastname: Rix
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, SE, 10691, Stockholm, Germany.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Foster
authors.affiliation: Laboratory for Molecular Microbial Ecology (LaMME), Marine Science Station, Aqaba, 77110, Jordan.|Department of Marine Biology, The University of Jordan - Aqaba Branch, Aqaba, 77110, Jordan.
authors.forename: Mamoon M D
authors.initials: MM
authors.lastname: Al-Rshaidat
authors.affiliation: Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, DE, 28359, Bremen, Germany.|Faculty of Biology and Chemistry (FB 2), University of Bremen, DE, 28359, Bremen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Wild
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000378:metabolism / Q000382:microbiology / Q000469:parasitology; D001419:Bacteria / Q000254:growth & development / Q000378:metabolism*; D004141:Dinoflagellida / Q000254:growth & development / Q000378:metabolism*; D057232:Global Warming; D052836:Heterotrophic Processes; D006358:Hot Temperature; D064307:Microbiota / Q000502:physiology; D009586:Nitrogen Fixation / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology; D013312:Stress, Physiological / Q000502:physiology; D013559:Symbiosis / Q000502:physiology