title: Skeletal light-scattering accelerates bleaching response in reef-building corals.
abstract: BACKGROUND
  At the forefront of ecosystems adversely affected by climate change, coral reefs are sensitive to anomalously high temperatures which disassociate (bleaching) photosynthetic symbionts (Symbiodinium) from coral hosts and cause increasingly frequent and severe mass mortality events. Susceptibility to bleaching and mortality is variable among corals, and is determined by unknown proportions of environmental history and the synergy of Symbiodinium- and coral-specific properties. Symbiodinium live within host tissues overlaying the coral skeleton, which increases light availability through multiple light-scattering, forming one of the most efficient biological collectors of solar radiation. Light-transport in the upper ~200 μm layer of corals skeletons (measured as 'microscopic' reduced-scattering coefficient, μ'(S,m)), has been identified as a determinant of excess light increase during bleaching and is therefore a potential determinant of the differential rate and severity of bleaching response among coral species.
  
  
  RESULTS
  Here we experimentally demonstrate (in ten coral species) that, under thermal stress alone or combined thermal and light stress, low-μ'(S,m) corals bleach at higher rate and severity than high-μ'(S,m) corals and the Symbiodinium associated with low-μ'(S,m) corals experience twice the decrease in photochemical efficiency. We further modelled the light absorbed by Symbiodinium due to skeletal-scattering and show that the estimated skeleton-dependent light absorbed by Symbiodinium (per unit of photosynthetic pigment) and the temporal rate of increase in absorbed light during bleaching are several fold higher in low-μ'(S,m) corals.
  
  
  CONCLUSIONS
  While symbionts associated with low-[Formula: see text] corals receive less total light from the skeleton, they experience a higher rate of light increase once bleaching is initiated and absorbing bodies are lost; further precipitating the bleaching response. Because microscopic skeletal light-scattering is a robust predictor of light-dependent bleaching among the corals assessed here, this work establishes μ'(S,m) as one of the key determinants of differential bleaching response.
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.|Department of Zoology, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL, 60605, USA.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Swain
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.|Department of Zoology, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL, 60605, USA.
authors.forename: Emily
authors.initials: E
authors.lastname: DuBois
authors.affiliation: Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Gomes
authors.affiliation: Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
authors.forename: Valentina P
authors.initials: VP
authors.lastname: Stoyneva
authors.affiliation: Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Radosevich
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.|Department of Zoology, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL, 60605, USA.
authors.forename: Jillian
authors.initials: J
authors.lastname: Henss
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.|Department of Zoology, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL, 60605, USA.
authors.forename: Michelle E
authors.initials: ME
authors.lastname: Wagner
authors.affiliation: Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Derbas
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
authors.forename: Hannah W
authors.initials: HW
authors.lastname: Grooms
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Velazquez
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
authors.forename: Joshua
authors.initials: J
authors.lastname: Traub
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Kennedy
authors.affiliation: Keck Biophysics Facility, Northwestern University, 633 Clark Street, Evanston, IL, 60208, USA.
authors.forename: Arabela A
authors.initials: AA
authors.lastname: Grigorescu
authors.affiliation: Department of Zoology, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL, 60605, USA.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Westneat
authors.affiliation: Fishes Department, John G. Shedd Aquarium, 1200 South Lake Shore Drive, Chicago, IL, 60605, USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Sanborn
authors.affiliation: Fishes Department, John G. Shedd Aquarium, 1200 South Lake Shore Drive, Chicago, IL, 60605, USA.
authors.forename: Shoshana
authors.initials: S
authors.lastname: Levine
authors.affiliation: Fishes Department, John G. Shedd Aquarium, 1200 South Lake Shore Drive, Chicago, IL, 60605, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Schick
authors.affiliation: Fishes Department, John G. Shedd Aquarium, 1200 South Lake Shore Drive, Chicago, IL, 60605, USA.
authors.forename: George
authors.initials: G
authors.lastname: Parsons
authors.affiliation: Division of Water Resource Management, Florida Department of Environmental Protection, 2600 Blair Stone Road, Tallahassee, 32399, USA.
authors.forename: Brendan C
authors.initials: BC
authors.lastname: Biggs
authors.affiliation: Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Rogers
authors.affiliation: Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
authors.forename: Vadim
authors.initials: V
authors.lastname: Backman
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA. l-marcelino@northwestern.edu.|Department of Zoology, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL, 60605, USA. l-marcelino@northwestern.edu.
authors.forename: Luisa A
authors.initials: LA
authors.lastname: Marcelino
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000502:physiology* / Q000528:radiation effects*; D057894:Coral Reefs; D004141:Dinoflagellida / Q000502:physiology*; D008027:Light; D038761:Photobleaching; D012542:Scattering, Radiation; D013559:Symbiosis; D013696:Temperature
keywords: Coral bleaching; Global climate change; Optical scattering; Photosynthesis; Symbiosis