To investigate and compare the trophic structures of hydrothermal vent communities at different depths, the carbon and nitrogen stable isotope ratios of dominant species were analyzed in the communities at Myojin Knoll (1,220-1,360 m) in the Izu-Ogasawara Arc and the Nikko Seamount (380-550 m) in the North Mariana Arc. At the Myojin knoll, a barnacle, Ashinkailepas seepiophila had high δ15N value, which suggested to be derived from photosynthetic products. Similarly, at Nikko Seamount, a polynoid polychaete, Gandulfus yunohana, a xanthid crab, Alvinocaaris sp., and Symphurus thermophilus had high δ15N values. These animals, too, are suggested to consume photosynthetic products. The range of δ13C values at Myojin Knoll was wider than that at Nikko Seamount. The difference between the ranges of these values suggest that different chemical environments between the two vent sites influence the components and distribution of chemoautotrophic bacteria found at each site, leading to different faunal compositions.
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