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Open AccessArticle

Organic Carbon and Nitrogen Isoscapes of Reef Corals and Algal Symbionts: Relative Influences of Environmental Gradients and Heterotrophy

1
Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwanoha 5-1-5, Kashiwa 277-8564, Japan
2
School of Environment and Society, Tokyo Institute of Technology, O-okayama 2-12-1 W8-13, Meguro, Tokyo 152-8552, Japan
*
Author to whom correspondence should be addressed.
Present affiliation: Sanyo Trading Co., Ltd. (T.F.); Faculty of Science, Universiti Brunei Darussalam, Brunei (Y.T.); Yakult Central Institute (K.M.); The Ocean Policy Research Institute, Sasakawa Peace Foundation (A.W.).
Microorganisms 2020, 8(8), 1221; https://doi.org/10.3390/microorganisms8081221
Received: 9 July 2020 / Revised: 7 August 2020 / Accepted: 9 August 2020 / Published: 11 August 2020
The elemental (C/N) and stable isotopic (δ13C, δ15N) compositions and compound-specific δ15N values of amino acids (δ15NAA) were evaluated for coral holobionts as diagnostic tools to detect spatiotemporal environmental heterogeneity and its effects on coral health. Hermatypic coral samples of eight species were collected at 12 reef sites with differing levels of pollution stress. The C/N ratios, δ13C values, and δ15N values of coral tissues and endosymbiotic algae were determined for 193 coral holobionts, and the amino acid composition and δ15NAA values of selected samples were analyzed. δ15N values were influenced most by pollution stress, while C/N ratios and δ13C values depended most strongly on species. The results imply that δ13C and δ15N values are useful indicators for distinguishing the ecological niches of sympatric coral species based on microhabitat preference and resource selectivity. Using δ15NAA values, the trophic level (TL) of the examined coral samples was estimated to be 0.71 to 1.53, i.e., purely autotrophic to partially heterotrophic. Significant portions of the variation in bulk δ15N and δ13C values could be explained by the influence of heterotrophy. The TL of symbionts covaried with that of their hosts, implying that amino acids acquired through host heterotrophy are translocated to symbionts. Dependence on heterotrophy was stronger at polluted sites, indicating that the ecological role of corals changes in response to eutrophication. View Full-Text
Keywords: carbon isotopes; compound-specific isotope ratios of amino acids; hermatypic coral; heterotrophy; microhabitat; nitrogen isotopes; Symbiodinium; terrestrial nutrient input carbon isotopes; compound-specific isotope ratios of amino acids; hermatypic coral; heterotrophy; microhabitat; nitrogen isotopes; Symbiodinium; terrestrial nutrient input
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MDPI and ACS Style

Fujii, T.; Tanaka, Y.; Maki, K.; Saotome, N.; Morimoto, N.; Watanabe, A.; Miyajima, T. Organic Carbon and Nitrogen Isoscapes of Reef Corals and Algal Symbionts: Relative Influences of Environmental Gradients and Heterotrophy. Microorganisms 2020, 8, 1221.

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