GEOCHEMICAL AND BIOGEOCHEMICAL PECULARITI ES OF BOTTOM FAUNA OF THE HYDROTHERMAL ASSOCIATION OF THE MANUS BASIN

The results of chemical, radioisotopic (C-14), microbiological and geo chemical isotopic (deltaC-13) studies of fauna biomass of the extremal ecosystem of active hydrothermal fields in the Manus basin are presen ted. Gastropoda of different species are dominant in the studied assoc iation. deltaC-13 values of three Gastropoda species (O. tuffari, O. h essleri, Turridae) are confined to a narrow range (-30.6 divided-by 37 .1%) and are near to that of Bivalvia biomass of the hydrothermal asso ciation of other oceanic areas. This fact could be interpreted by the presence of chemoautotrophic and methanetrophic microorganisms as init ial members of a trophic chain in the hydrothermal fauna association. Such types of organisms are known to have an abnormal carbon isotopic composition in relation to the photosynthesied oceanic organic matter. It was carried out that in certain cases chemoautotrophic and/or meth anetrophic bacteria should be concerned as endosimbionts providing the simbiotrophic type of Mollusca and other fauna. In other cases organo trophic mollusca use for food the benthos and/or plankton chemosynthet ic and methanetrophic organisms. Carbon isotopic data of the biomass c ould be used for the search of the source of carbon used for food. The application data apart from other investigation methods could lead to errors in the search of feeding type of organisms in hydrothermal and other extremal associations.