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Marine Ecology Progress Series

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MEPS 540:157-165 (2015)  -  DOI:

Re-evaluation of nutrient sources for deep-sea wood-boring bivalves using the isotopic composition of bulk C, N, S, and amino acid nitrogen

Toshiro Yamanaka1,*, Sho Shimamura1,4, Yoshito Chikaraishi2, Takuma Haga3, Yoshihiro Fujiwara2

1Graduate school of Natural Science and Technology, Okayama University, 1-1 Naka 3-chome, Tsushima, Kita-ku, Okayama 700-8530, Japan
2Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan
3Toyohashi Museum of Natural History, 1-238 Oana, Oiwa, Toyohashi 441-3147, Japan
4Present address: Japan Meteorological Agency, 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan
*Corresponding author:

ABSTRACT: Wood-boring bivalves (families Xylophagaidae and Teredinidae) are unique bivalves that are peculiarly adapted to feed on terrigenous woody materials, even though they inhabit the deep-sea floor far from land. Previous studies of their metabolic processes suggested the importance of symbiotic microbes that secrete cellulase to access woody carbon (carbohydrates), and supply organic nitrogen via nitrogen fixation. Since nitrogen is generally depleted in woody materials, dissolved dinitrogen in seawater has been proposed as a plausible nitrogen source for wood-boring bivalves. We evaluated the food ecology of wood-boring bivalves (genus: Xyloredo) obtained from the deep seafloor off the Ryukyu Islands by considering their bulk carbon, nitrogen, and sulfur isotope composition and potential dietary sources (i.e. logs, particulate organic matter, and surface sediments). We also investigated the trophic interactions between wood-boring bivalves and logs based on the amino acid nitrogen isotopic composition. The bulk isotope data revealed that in wood-boring bivalves these elements are derived mainly from the logs in which they live. These results were consistent with the trophic hierarchy calculated from the nitrogen isotopic composition of amino acids. Ecologically, wood-boring bivalves are one step higher than logs in terms of their trophic position. Based on these data, we propose that terrigenous woody materials are the major dietary sources for wood-boring bivalves and the same standard trophic interaction exists between diet and consumer species as in the grazing food web. The symbionts may aid the digestion of woody materials, but they do not supply nitrogen via nitrogen fixation in this case.

KEY WORDS: Wood-boring bivalves · Xyloredo teramachii · Compound-specific nitrogen isotope analysis · Amino acids · Nitrogen nutrition · Stable isotope composition

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Cite this article as: Yamanaka T, Shimamura S, Chikaraishi Y, Haga T, Fujiwara Y (2015) Re-evaluation of nutrient sources for deep-sea wood-boring bivalves using the isotopic composition of bulk C, N, S, and amino acid nitrogen. Mar Ecol Prog Ser 540:157-165.

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