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Marine Ecology Progress Series

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MEPS 216:119-127 (2001)  -  doi:10.3354/meps216119

Exploitation of a chemosynthetic food resource by the polychaete Capitella sp. I

Hiroaki Tsutsumi1,*, Sam Wainright2, Shigeru Montani3, Megumi Saga1, Sagiri Ichihara1, Kazuhiro Kogure4

1Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, 3-1-100 Tsukide, Kumamoto 862, Japan
2US Coast Guard Academy, 15 Mohegan Avenue, New London, Connecticut 06320-8100, USA
3Faculty of Agriculture, Kagawa University, Ikedo, Kida-gun, Kagawa-ken 761-07, Japan
4Ocean Research Institute, Tokyo University, 1-15-1 Minamidai, Shinjuku-ku, Tokyo 164, Japan

ABSTRACT: In organically enriched sediments of coastal areas, sulfate-reducing bacteria decompose organic matter anaerobically, producing high levels of hydrogen sulfide. Chemoautotrophic sulfur-oxidizing bacteria proliferate at the sulfide/oxygen interface and use hydrogen sulfide as an electron donor. A few species of small polychaete worms, including Capitella sp. I, often dominate the macrofaunal benthic communities in such sulfide-rich environments in the organically enriched sediments. In this study, we conducted 2 laboratory experiments to determine whether Capitella sp. I can benefit trophically through the exploitation of the organic matter chemosynthetically produced by sulfur-oxidizing bacteria. In the first experiment, we reared juveniles of Capitella sp. I with natural sediment of very low organic content, with no additional organic matter, under dark conditions, and exposed them to 3 different levels of sodium sulfide. The worms reared in the sulfide treatments showed better survival, enhanced growth and reproduction. They had lower δ13C values (-24.3”, mean) than control worms (-20.1”, mean) and the sediments in which the worms were cultured (-21.4”, mean). The distinctive δ13C signature of the worms in the sulfide treatments indicates that they did not share the same carbon source as the control worms. The second experiment was done in the same manner as the first, but the carbonate in the water was replaced with 13CO2 in order to trace the autotrophic fixation of carbon dioxide by chemosynthetic bacteria occurring within the sediments. The results indicate that fixation of 13CO2 was promoted in sediments with Na2S amendments, and further enhanced by the presence of Capitella sp. I. The worms in these sediments had extremely high δ13C values (+5218.2”). The results of this study introduce the possibility of enhanced survival and growth of Capitella sp. I in sulfide-rich environments in the organically enriched sediments, facilitated by its utilization of a novel source of organic matter.

KEY WORDS: Capitella · Chemoautotrophic bacteria · Stable isotope · Organic enrichment · 13C · 15N

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