title: Effect of UV radiation on the expulsion of Symbiodinium from the coral Pocillopora damicornis.
abstract: The variation in density of the symbiotic dinoflagellate Symbiodinum in coral is a basic indicator of coral bleaching, i.e. loss of the symbiotic algae or their photosynthetic pigments. However, in the field corals constantly release their symbiotic algae to surrounding water. To explore the underlying mechanism, the rate of expulsion of zooxanthellae from the coral Pocillopora damicornis was studied over a three-day period under ultraviolet radiation (UVR, 280-400nm) stress. The results showed that the algal expulsion rate appeared 10-20% higher under exposure to UV-A (320-395nm) or UV-B (295-320nm), though the differences were not statistically significant. When corals were exposed to UV-A and UV-B radiation, the maximum expulsion of zooxanthellae occurred at noon (10:00-13:00), and this timing was 1h earlier than in the control without UVR. UVR stress led to obvious decreases in the concentrations of chl a and carotenoids in the coral nubbins after a three-day exposure. Therefore, our results suggested that although the UVR effect on algal expulsion rate was a chronic stress and was not significant within a time frame of only three days, the reduction in chl a and carotenoids may potentially enhance the possibility of coral bleaching over a longer period.
authors.affiliation: State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Key Laboratory of Tropical Marine Bio-resources and Ecology, Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China; Tropical Marine Biological Research Station in Hainan, Chinese Academy of Sciences, Sanya, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Huang
authors.affiliation: State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian, China; School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: John
authors.initials: J
authors.lastname: Beardall
authors.affiliation: State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian, China. Electronic address: ksgao@xmu.edu.cn.
authors.forename: Kunshan
authors.initials: K
authors.lastname: Gao
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000378:metabolism / Q000469:parasitology / Q000528:radiation effects*; D002338:Carotenoids / Q000378:metabolism; D002940:Circadian Rhythm; D004141:Dinoflagellida / Q000502:physiology / Q000528:radiation effects*; D010788:Photosynthesis; D010860:Pigments, Biological / Q000378:metabolism; D013559:Symbiosis; D014466:Ultraviolet Rays
chemical_list: D010860:Pigments, Biological; D002338:Carotenoids
keywords: Coral; Expulsion; Pocillopora damicornis; Ultraviolet radiation