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 Island, New Hebrides, Raul Island, Kermadek Island and the ‘Calypso’ gas anomaly area, Bay of Plenty, New Zealand, being enriched with methane and 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 Whale and White Islands (New Zealand), as well as in Matupi Harbour Bay (New Britain Island), significant rates of microbial chemosynthesis were recorded in the water column (5–10 mg C m−3 day−1. This was reflected 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 hydrotherms. Primary phytoplankton production in these waters was significantly 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 influenced by hydrotherms (Whale Island) contained a large percentage of planktonic amoebae, up to 30 × 103 I−1. The probable ways in which shallow hydrothermal discharges influence the biota of coastal waters are discussed.