AB 18:125-139 (2013)  -  DOI: https://doi.org/10.3354/ab00496

Respiratory electron transport system activity in symbiotic corals and its link to calcification

Sylvain Agostini1,5,*, Hiroyuki Fujimura1, Kazuhiko Fujita2, Yoshimi Suzuki3, Yoshikatsu Nakano4

1Department of Chemistry, Biology and Marine Science, University of the Ryukyus, 1 Senbaru, Nishihara-cho, Okinawa 903-0213, Japan
2Department of Physics and Earth Science, University of the Ryukyus, 1 Senbaru, Nishihara-cho, Okinawa 903-0213, Japan
3Graduate School of Science and Technology, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan
4Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, 3422 Sesoko, Motobu, Okinawa 905-0227, Japan
5Present address: Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka 415-0025, Japan

ABSTRACT: Scleractinian corals host photosynthetic endosymbionts, making direct measurement of the host respiration rate via incubation methods based on O2 consumption impossible. We tested the use of the respiratory electron transport system activity (ETSA) for measuring host potential respiration. The applied method, modified from a previous study, is based on the reduction of (4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride (INT) to formazan. After the development of a protocol suitable for corals, the method was tested on 5 different species. Metabolism, including photosynthesis, dark respiration and light and dark calcification, was measured through incubation. Host and zooxanthellae fractions were separated and their ETSAs, protein contents and zooxanthellae densities were measured. Mean ETSA/dark respiration (ETSA/R) ratios for host corals ranged from 1.7 ± 0.2 to 3.5 ± 0.6, while ratios for zooxanthellae ranged from 3.7 to 7.8. The high ratios observed for zooxanthellae indicate that their respiration may be 5 times higher under light conditions than in the dark. Considering the obtained ratios, host respiration in light could increase at most by a factor of 3.5 compared with dark respiration rates. Ratios close to 1 were found for some specimens, which suggests that higher respiration rates under light compared with dark conditions are not possible. Therefore, increased respiration in light cannot explain the observed enhancement of calcification under light conditions. ETSA was correlated with zooxanthellae density, suggesting adaptation of the levels of host ETS enzymes to the amount of translocated photosynthetates under optimal conditions. Estimated dark host respiration was correlated with photosynthesis, which suggests that it is determined mainly by the amount of energy available but also the amount of electron transport system enzymes. This constrains the amount of ATP available for calcification. Hence, we propose a mechanism by which respiration limits the calcification rate.


KEY WORDS: Electron transport system · ETS · Respiration · Calcification · Symbiotic corals


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Cite this article as: Agostini S, Fujimura H, Fujita K, Suzuki Y, Nakano Y (2013) Respiratory electron transport system activity in symbiotic corals and its link to calcification. Aquat Biol 18:125-139. https://doi.org/10.3354/ab00496

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