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

Abstract

A dense commnrty of benthc animals was discovered by the Japanese ROV 'Kaiko' in the hadal Zone near the bottamaf the Japan Trench, 7326 m deep. The community was dorninated by a new species of thyasind h a l v e Maorithyas hadalis. This comrnunity appears to be sustained by chemosynthesis (nutrients b b e m g derived from reduced compounds within the sediment) for reasons including: a high c o n c e n t r a t h of sulfur contained in the thyasind giils; the existente of numerous bactena-like particles in the gdi ssues; a suiiide smell from soft body parts and from coiiected sediment; the anoxic nature and high m d e content of the sediments suggested by the dark gray to black color; the occurrence above geologic laults. Thyasinds have also been collected frorn other chemosynthesisbased communities a r o u d Japan, including the Japan Trench, Sagami Bay and the Nankai accretionary pnsm. Until now, the deepest chemosynthesis-based community known occurred on the Sanriku Escarpment of thb Japan Trench, 6437 m deep. This site was dominated by the vesicomyid clam Calyptogena phaseaTarpuarPUs. The discovery of a chemosynthesis-based comrnunity dominated by thyasirid clams from even cbeper waters suggests a wider vanety of chemosynthesis-based cornmunities exists throughout deep-sea trenches. Additionally, the thyasind species discussed here differs from other thyasinds by having drcular symbionts which appear to exist intracellularly, and by living exposed above the sediment snuiace.