Effect of shallow-water hydrothermal venting on the biota of Matupi Harbour (Rabaul Caldera, New Britain Island, Papua New Guinea)

Coastal hydrothermal vents in the depth range 0-27 m were studied in Matupi Harbour, a marine bight that is partly isolated from the open sea on the n orth-east coast of New Britain, Papua New Guinea, where volcanoes are activ e. Planktonic and benthic communities (including bacteria) in the Harbour w ere compared with adjacent fully marine areas. The environmental parameters assessed included temperature, salinity, O-2, H-2, hydrocarbons, metals, s ome species of nitrogen and sulphur, inorganic phosphate, silicate and chlo rophyll a. There was pronounced stratification of the waters in the Harbour as a result of inflow of heated volcanic fluids, most evident in the surfa ce 0-3 m layer. The volcanic fluids are rich in phytoplankton nutrients and reduced compounds which stimulate growth of bacterial plankton, bacterial production and enhance primary production. The highest values of photosynth etic fixation (almost 100 mg C m(3) d) and bacterial production (216 mg C m (3) d) found in the Harbour are much greater than previously reported for m arine ecosystems. The chemosynthetic fraction of bacterial production varie d from 15 to 60%, with highest values in the surface and the near-bottom la yers, The zooplankton in the Harbour was dominated by cyclopoid copepods an d was low in diversity. Bacterial mats were very evident at the areas of ve nting, dominated by Thiodendron-like species, but both epifauna and infauna were sparse at the vents. However, areas adjacent to the hydrothermal vent s showed the richest benthic communities, with epifauna dominated by corals and sponges and infauna by nematodes. It appeared that benthic community d evelopment was inhibited by the hot sediment, rapid sedimentation, lack of hard substratum and large numbers of sponge spicules in the sediment. From dating of the last major volcanic eruption (1943), the Harbour provides an excellent model for studying processes of succession and adaptation in mari ne communities stressed by shallow-water gasohydrothermal activity. (C) 199 8 Elsevier Science Ltd. All rights reserved.