MICROPLANKTON AND ITS FUNCTIONAL-ACTIVITY IN ZONES OF SHALLOW HYDROTHERMS IN THE WESTERN PACIFIC

Water above the active underwater volcanoes on the slopes of Epi Islan d, New Hebrides, Paul Island, Kermadek Island and the 'Calypso' gas an omaly area, Bay of Plenty, New Zealand, being enriched with methane an d hydrogen, contains abundant bacterioplankton with a biomass several times greater than the surrounding oceanic waters. Dark microbial CO2 uptake in these sites was 10-30 times greater than in adjacent oceanic waters. In the shallow underwater volcanic hydrotherm areas around Wh ale and White Islands (New Zealand), as well as in Matupi Harbour Bay (New Britain Island), significant rates of microbial chemosynthesis we re recorded in the water column (5-10 mg C m(-3) day(-1)). This was re flected in high microbial biomass: 20-60 mg C m(-3). Over the field of algal-bacterial mats, it exceeded 100 mg C m(-3). The cell volume of bacteria growing in waters influenced by hydrothermal activity was 2-4 times greater than that of those growing in sea areas remote from hyd rotherms. Primary phytoplankton production in these waters was signifi cantly greater than in surrounding oceanic waters. A high activity of hydrogen- and methane-oxidizing bacteria, as,well as thiobacilli, was also recorded there. The microzooplankton in areas of the sea influenc ed by hydrotherms (Whale Island) contained a large percentage of plank tonic amoebae, up to 30 x 10(3) l(-1). The probable ways in which shal low hydrothermal discharges influence the biota of coastal waters are discussed.