Habitat mapping for the deep-sea megafauna around cobalt-rich ferromanganese crusts in the Xufu Guyot of the northwestern Pacific

In this study, to perform habitat mapping of megafauna around cobalt-rich ferromanganese crustson the deep-sea floor, we identified substrate types and megafauna around Xufu Guyot ( JA06 seamount) in the northwestern Pacific and analyzed their spatial distribution patterns by using Finder installed Deep-sea Camera (FDC). We set three transects with a total length of 37.4 km from base to flat-top of the seamount that ranged ca. 1,300 - 3,600 m in depth. We detected 4,964 individuals and identified 53 Operational Taxonomic Units (OTUs) across seven phyla with 16 classes in total. Densities of megafauna ranged between 82.6 - 163.9 individuals/km. We mapped substrate types, by setting three categories according to the ratio of hard rocks, and megafaunal distribution patterns. Results showed that sessile organisms (e.g. Porifera, Gorgonacea) were frequently observed not only in sites with higher ratio of hard rocks but also in those with lower ratio of hard rocks. We also detected significant aggregated patterns in many organisms. Multiple aggregated sites were observed in sessile organisms which are directly affected by mineral resource development. It is, therefore, important to elucidate source-sink relationship among these sites of these organisms for the establishment of preservation reference zones.