62 - Habitats of the Su Su Knolls Hydrothermal Site, Eastern Manus Basin, Papua New Guinea

Abstract

The Manus Basin is a rapidly opening (∼10 cm/yr) back-arc basin located between directionally opposed fossil and active subduction zones The basin, as a whole, tectonically lies within the zone of convergence between the Australian and Pacific plates and is composed of two smaller fragments: the North and South Bismarck microplates. Su Su Knolls, located in the eastern Manus Basin, Bismarck Sea, Papua New Guinea, is comprised of three volcanic domes cresting between 1,150 and 1,520 m below sea level. The main geomorphic features examined are hydrothermally generated mounds associated with the development of polymetallic seafloor massive sulfide occurrences. The main habitat types are soft (sediment) and hard (rock) substrates, which can be further categorized by whether or not they are under the influence of current hydrothermal activity. Biological activity and types of animals present are primarily affected by proximity to active venting, with those associated with hydrothermal vents having a chemosynthetic base to their food chain. Predictive mapping using bathymetry alone would have difficulty distinguishing between substrates either near or away from active venting. Although additional indirect observation methods would add to any evaluation, direct observation of the seafloor is needed to conclusively distinguish between habitats. Active hydrothermal vents tend to support a higher abundance of fauna, although of lower diversity, compared to dormant vents and the surrounding deep-sea environments. Where there are active hydrothermal areas, one of the main contributing factors to the biology present is the chemistry of the fluid being emitted. Benthic communities in the immediate vicinity of the hydrothermal vents are based on chemosynthesis, where energy is derived from chemical nutrients rather than sunlight.