title: Differential coral bleaching-Contrasting the activity and response of enzymatic antioxidants in symbiotic partners under thermal stress.
abstract: Mass coral bleaching due to thermal stress represents a major threat to the integrity and functioning of coral reefs. Thermal thresholds vary, however, between corals, partly as a result of the specific type of endosymbiotic dinoflagellate (Symbiodinium sp.) they harbour. The production of reactive oxygen species (ROS) in corals under thermal and light stress has been recognised as one mechanism that can lead to cellular damage and the loss of their symbiont population (Oxidative Theory of Coral Bleaching). Here, we compared the response of symbiont and host enzymatic antioxidants in the coral species Acropora millepora and Montipora digitata at 28°C and 33°C. A. millepora at 33°C showed a decrease in photochemical efficiency of photosystem II (PSII) and increase in maximum midday excitation pressure on PSII, with subsequent bleaching (declining photosynthetic pigment and symbiont density). M. digitata exhibited no bleaching response and photochemical changes in its symbionts were minor. The symbiont antioxidant enzymes superoxide dismutase, ascorbate peroxidase, and catalase peroxidase showed no significant upregulation to elevated temperatures in either coral, while only catalase was significantly elevated in both coral hosts at 33°C. Increased host catalase activity in the susceptible coral after 5days at 33°C was independent of antioxidant responses in the symbiont and preceded significant declines in PSII photochemical efficiencies. This finding suggests a potential decoupling of host redox mechanisms from symbiont photophysiology and raises questions about the importance of symbiont-derived ROS in initiating coral bleaching.
authors: School of Biological Sciences, Victoria University of Wellington, Wellington 6140, New Zealand; Laboratory for Biological Geochemistry, School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015, Switzerland. Electronic address: thomas.krueger@epfl.ch.
authors: Thomas
authors: T
authors: Krueger
authors: School of Biological Sciences, Victoria University of Wellington, Wellington 6140, New Zealand; College of Earth, Ocean and Environment, University of Delaware, Lewes, DE 19958, USA. Electronic address: thawkins@udel.edu.
authors: Thomas D
authors: TD
authors: Hawkins
authors: School of Biological Sciences, Victoria University of Wellington, Wellington 6140, New Zealand. Electronic address: susanne.becker25@gmail.com.
authors: Susanne
authors: S
authors: Becker
authors: School of Biological Sciences, Victoria University of Wellington, Wellington 6140, New Zealand. Electronic address: steffipont@gmail.com.
authors: Stefanie
authors: S
authors: Pontasch
authors: School of Biological Sciences & ARC Centre of Excellence for Coral Reef Studies, University of Queensland, Brisbane, QLD 4072, Australia. Electronic address: s.dove@cms.uq.edu.au.
authors: Sophie
authors: S
authors: Dove
authors: Global Change Institute, University of University of Queensland, Brisbane, QLD 4072, Australia. Electronic address: oveh@uq.edu.au.
authors: Ove
authors: O
authors: Hoegh-Guldberg
authors: Comparative Genomics Centre, School of Pharmacy and Molecular Sciences & ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia. Electronic address: bill.leggat@jcu.edu.au.
authors: William
authors: W
authors: Leggat
authors: School of Biological Sciences, Victoria University of Wellington, Wellington 6140, New Zealand; School of Civil Engineering, University of Queensland, St Lucia, QLD 4072, Australia. Electronic address: p.fisher@uq.edu.au.
authors: Paul L
authors: PL
authors: Fisher
authors: School of Biological Sciences, Victoria University of Wellington, Wellington 6140, New Zealand. Electronic address: simon.davy@vuw.ac.nz.
authors: Simon K
authors: SK
authors: Davy
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000254:growth & development / Q000469:parasitology / Q000502:physiology* / Q000528:radiation effects; D060387:Ascorbate Peroxidases / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D057894:Coral Reefs; D004141:Dinoflagellida / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D006358:Hot Temperature / Q000009:adverse effects; D018384:Oxidative Stress; D010140:Pacific Ocean; D038761:Photobleaching / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010860:Pigments, Biological / Q000378:metabolism*; D015800:Protozoan Proteins / Q000378:metabolism; D011793:Queensland; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013045:Species Specificity; D013312:Stress, Physiological / Q000528:radiation effects; D013472:Sunlight / Q000009:adverse effects; D013482:Superoxide Dismutase / Q000378:metabolism; D013559:Symbiosis / Q000528:radiation effects
chemical_list: D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D015800:Protozoan Proteins; D017382:Reactive Oxygen Species; D060387:Ascorbate Peroxidases; D002374:Catalase; D013482:Superoxide Dismutase
keywords: APX; Acropora millepora; CAT; Global change; Montipora digitata; Oxidative stress; SOD; Symbiodinium; Symbiosis; Thermal biology