title: Long-term salinity tolerance is accompanied by major restructuring of the coral bacterial microbiome.
abstract: Scleractinian corals are assumed to be stenohaline osmoconformers, although they are frequently subjected to variations in seawater salinity due to precipitation, freshwater run-off and other processes. Observed responses to altered salinity levels include differences in photosynthetic performance, respiration and increased bleaching and mortality of the coral host and its algal symbiont, but a study looking at bacterial community changes is lacking. Here, we exposed the coral Fungia granulosa to strongly increased salinity levels in short- and long-term experiments to disentangle temporal and compartment effects of the coral holobiont (i.e. coral host, symbiotic algae and associated bacteria). Our results show a significant reduction in calcification and photosynthesis, but a stable microbiome after short-term exposure to high-salinity levels. By comparison, long-term exposure yielded unchanged photosynthesis levels and visually healthy coral colonies indicating long-term acclimation to high-salinity levels that were accompanied by a major coral microbiome restructuring. Importantly, a bacterium in the family Rhodobacteraceae was succeeded by Pseudomonas veronii as the numerically most abundant taxon. Further, taxonomy-based functional profiling indicates a shift in the bacterial community towards increased osmolyte production, sulphur oxidation and nitrogen fixation. Our study highlights that bacterial community composition in corals can change within days to weeks under altered environmental conditions, where shifts in the microbiome may enable adjustment of the coral to a more advantageous holobiont composition.
authors: Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia.
authors: Till
authors: T
authors: Röthig
authors: Biological and Organometallic Catalysis Laboratories, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia.
authors: Michael A
authors: MA
authors: Ochsenkühn
authors: Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia.
authors: Anna
authors: A
authors: Roik
authors: Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia.
authors: Riaan
authors: R
authors: van der Merwe
authors: Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia.
authors: Christian R
authors: CR
authors: Voolstra
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000818:Animals; D037421:Anthozoa / Q000382:microbiology* / Q000502:physiology*; D001419:Bacteria / Q000145:classification; D004269:DNA, Bacterial / Q000235:genetics; D064307:Microbiota; D010788:Photosynthesis; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D054712:Salinity; D055049:Salt Tolerance; D013559:Symbiosis
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S
keywords: Fungia granulosa; Red Sea; bacterial community profiling; coral holobiont; coral reef; microbiome