BACTERIAL CHEMOSYNTHESIS AND METHANOTROPHY IN THE MANUS AND LAU BASINS ECOSYSTEMS

The rates of bacterial CO2 accumulation and methane oxidation in activ e hydrothermal fields in the Manus Basin and the eastern Lau Basin hav e been determined. In the Manus Basin the rate of dark CO2 assimilatio n in plumes varied from 1200 to 2500 ng C l(-1) day(-1), where chemoli thoautotrophic processes prevail (93-97%). The rate of methane oxidati on in plumes did not exceed 1300 ng C l(-1) day(-1) and it dropped rap idly (30 x) with distance from the vent. In parts of the central and n orthern Lau Basin, rates of dark CO2 assimilation and methane oxidatio n were 1-2 orders lower. Comparison of biochemical process rates in th e bottom 350 m layer of water in plumes above active hydrothermal fiel ds in different areas of the rift system provides evidence of the glob al scale of processes of CO2 assimilation and the considerable contrib ution by primary chemosynthetic production to total organic matter pro duction in rift regions. (C) 1997 Elsevier Science B.V.