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Membrane Lipids of Symbiotic Algae Are Diagnostic of Sensitivity to Thermal Bleaching in Corals

Dan Tchernov, Maxim Y. Gorbunov, Colomban de Vargas, Swati Narayan Yadav, Allen J. Milligan, Max Häggblom, Paul G. Falkowski and Christopher B. Field
Proceedings of the National Academy of Sciences of the United States of America
Vol. 101, No. 37 (Sep. 14, 2004), pp. 13531-13535
Stable URL: http://www.jstor.org/stable/3373345
Page Count: 5
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Membrane Lipids of Symbiotic Algae Are Diagnostic of Sensitivity to Thermal Bleaching in Corals
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Abstract

Over the past three decades, massive bleaching events of zoox-anthellate corals have been documented across the range of global distribution. Although the phenomenon is correlated with relatively small increases in sea-surface temperature and enhanced light intensity, the underlying physiological mechanism remains unknown. In this article we demonstrate that thylakoid membrane lipid composition is a key determinate of thermal-stress sensitivity in symbiotic algae of cnidarians. Analyses of thylakoid membranes reveal that the critical threshold temperature separating thermally tolerant from sensitive species of zooxanthellae is determined by the saturation of the lipids. The lipid composition is potentially diagnostic of the differential nature of thermally induced bleaching found in scleractinian corals. Measurements of variable chlorophyll fluorescence kinetic transients indicate that thermally damaged membranes are energetically uncoupled but remain capable of splitting water. Consequently, a fraction of the photosynthetically produced oxygen is reduced by photosystem I through the Mehler reaction to form reactive oxygen species, which rapidly accumulate at high irradiance levels and trigger death and expulsion of the endosymbiotic algae. Differential sensitivity to thermal stress among the various species of Symbiodinium seems to be distributed across all clades. A clocked molecular phylogenetic analysis suggests that the evolutionary history of symbiotic algae in cnidarians selected for a reduced tolerance to elevated temperatures in the latter portion of the Cenozoic.

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