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Marine Ecology Progress Series

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MEPS 190:17-26 (1999)  -  doi:10.3354/meps190017

The deepest chemosynthesis-based community yet discovered from the hadal zone, 7326 m deep, in the Japan Trench

Katsunori Fujikura1,*, Shigeaki Kojima2, Kensaku Tamaki2, Yonosuke Maki3, James Hunt1, Takashi Okutani4

1Japan Marine Science and Technology Center, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
2Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan
3Faculty of Humanities and Society Science, Iwate University, 3-18-34 Ueda, Morioka-shi, Iwate 020-8550, Japan
4College of Bioresource Sciences, Nihon University, and Scientific adviser at Japan Marine Science and Technology Center, 1866 Kameino, Fujisawa-shi, Kanagawa 252-8510, Japan

ABSTRACT: A dense community of benthic animals was discovered by the Japanese ROV 'Kaiko' in the hadal zone near the bottom of the Japan Trench, 7326 m deep. The community was dominated by a new species of thyasirid bivalve Maorithyas hadalis. This community appears to be sustained by chemosynthesis (nutrients being derived from reduced compounds within the sediment) for reasons including: a high concentration of sulfur contained in the thyasirid gills; the existence of numerous bacteria-like particles in the gill tissues; a sulfide smell from soft body parts and from collected sediment; the anoxic nature and high sulfide content of the sediments suggested by the dark gray to black color; the occurrence above geologic faults. Thyasirids have also been collected from other chemosynthesis-based communities around Japan, including the Japan Trench, Sagami Bay and the Nankai accretionary prism. Until now, the deepest chemosynthesis-based community known occurred on the Sanriku Escarpment of the Japan Trench, 6437 m deep. This site was dominated by the vesicomyid clam Calyptogena phaseoliformis. The discovery of a chemosynthesis-based community dominated by thyasirid clams from even deeper waters suggests a wider variety of chemosynthesis-based communities exists throughout deep-sea trenches. Additionally, the thyasirid species discussed here differs from other thyasirids by having circular symbionts which appear to exist intracellularly, and by living exposed above the sediment surface.

KEY WORDS: Chemosynthesis-based community · Thyasirid clams · Hadal zone · Japan Trench

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