[M-ZZ42] Process, Environment, and Exploration of Marine Manganese Deposits

[MZZ42-03] Characteristics of megabenthic community on guyots in the Northwest Pacific observed using an FDC deep-tow camera system

Hiroko Kamoshida¹, Shogo Kato², Hiroyuki Yokooka², Keigo Yanagita³, Shohei Kikuta³, Shota Mitsui⁴, Jumpei Minatoya⁴, Akira Iguchi^5,6, Hiroki Kise⁷, *Atsushi Suzuki^5,6 (1. Japan Organization for Metals and Energy Security (JOGMEC), 2.IDEA Consultants, Inc., 3.Science and Technology Co., Ltd., 4.Marine Biological Research Institute of Japan Co., Ltd., 5.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 6.Research Laboratory on Environmentally-conscious Developments and Technologies [E-code], National Institute of Advanced Industrial Science and Technology (AIST), 7.Environmental Management Research Institute, National Institute of Advanced Industrial Science and Technology (AIST))

Keywords:seamount, megabenthos, deep-sea ecosystem

The Japan Organization for Metals and Energy Security (JOGMEC) signed an exploration contract for cobalt-rich ferromanganese crusts with the International Seabed Authority (ISA) in 2014. According to this contract, JOGMEC is ensured an exclusive right of exploration in the contracted area, which is located on the High Seas off southeastern Minami-Torishima Island, the Northwest Pacific. Megabenthos distribution on seamounts with JOGMEC’s contracted areas were examined from images obtained using a finder deep-tow camera (FDC, Finder-equipped deep-tow camera) system. The towing altitude is 2-3 m above the seafloor. To assess diversity of deep-sea megabenthos among seamounts, a total of ~12,000 individuals (colonies) of the megabenthos (covering 109 km in distance), was counted and classified into 43 morphotypes, which were dominated by crinoids, ophiuroids, hexactinellids and octocorals. The density of megabenthos is generally small, which may correspond to the small primary production at the surface in this area. In conjunction, megabenthos was also examined using remotely operated vehicles. Interestingly, gorgonians and sponges were found in high density along the ROV transects at Zhinyu and Maloney guyots. These so-called “coral gardens” and “sponge grounds” areas were found at the tops of small pinnacles distributed on the flat tops of seamounts. These pinnacles were approximately 1-2 km in diameter and had a relative elevation of 200-300 m above the surrounding seamount tops. High densities of organisms at peaks of a seamount have been reported in previous literature, and it is thought that increased local current velocities support the high abundance of megabenthos, which are primarily filter-feeders.