Wide Area 3D Visual Reconstructions to Survey the Distribution of Macrobenthos in Deep-sea Hydrothermal Vent Systems

Adrian Bodenmann, Institute of Industrial Science, The University of Tokyo, Blair Thornton, Institute of Industrial Science, The University of Tokyo, Tokyo, Japan, Ryota Nakajima, JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan, Stefan B Williams, The University of Sydney, Australian Centre for Field Robotics, Sydney, Australia, Oscar Pizarro, ACFR, University Of Sydney, Australia and Ken Takai, JAMSTEC, Yokosuka, Japan
Abstract:
Deep-sea hydrothermal systems often support large and diverse populations of vent-associated organisms. While these organisms are well adapted to surviving in dynamic and unstable environmental conditions, the interest in deep-sea mining raises concerns about the potential impacts of human activities on the health of these ecosystems. In this work, we describe a practical method to rapidly assess the distribution and diversity of macrobenthos over wide areas based on a two-phase multi-resolution visual mapping technique. The first phase maps wide areas of the seafloor from high altitudes of 10m at a rates > 10,000m2/h. The resolution of the data obtained during this phase is in the region of 1cm and is used to map the distribution of larger species that can be easily identified at this resolution. The data is also used to identify densely populated regions for more detailed mapping in the second phase. The second phase maps the seafloor from an altitude of 2m, covering 1000m2/h at a resolution of about 1mm and is used to map a larger number of species. The technique is applied to two areas in the Iheya North Field of the Okinawa trough, in regions that were extensively drilled during the IODP 331 expedition. A total area of more than 30,000m2 was mapped in a single dive with a remotely operated vehicle (ROV) and more than 80,000 organisms were identified from six different species. The data obtained forms the largest continuous 3D reconstructions of the seafloor mapped visually and the largest continuous dataset for the distribution of deep-sea macrobenthic organisms. The results give insight into the effects of human drilling activity on vent-ecosystems. The method described is a practical way to quantitatively assess the distribution of macrobenthic biomass over statistically meaningful spatial scales in a way that is repeatable and is suitable for comparison between sites or for monitoring sites over time.
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