ABSTRACT

The authors present preliminary results of shipboard observations of nodule fauna, consisting of deep-sea organisms living on the surface of polymetallic nodules distributed on the abyssal seafloor, from the western part of the Clarion-Clipperton Zone of the Pacific Ocean. Large-size nodule fauna, such as xenophyophore (more than two centimeters), which can be identified visually on the top view of a box corer, was examined on more than 1,000 nodules at thirteen sites. In addition, intermediate-size nodule fauna (mainly 1 to 10 mm), identified under a stereomicroscope, were observed on 47 nodules obtained at eight sites. Since intermediate-size nodule fauna was observed under methods that were different from those applied in previous studies, making quantitative comparisons with previous studies should be done with careful considerations. This paper describes some new findings, together with applicability of the methods used for observing nodule fauna.

INTRODUCTION

Polymetallic nodules (manganese nodules) in the deep-sea have been gaining great interest because they contain economically valuable elements, such as cobalt, copper, manganese, and nickel. As the Clarion-Clipperton Zone (CCZ) in the Pacific Ocean is particularly known to have high abundance of nodules and a high metal grade (e.g., Morgan, 2000), many exploration activities have been conducted there. Since the CCZ is located within international waters, i.e., an area beyond the limits of national jurisdiction, any exploration activities fall under the control of the International Seabed Authority (ISA). "Contractors," that are under contract with the ISA for exploration activities in the CCZ, have been conducting survey cruises in their contract areas approved by the ISA. In terms of the Japanese area of the CCZ, the contract for exploration activities in this area has been granted by the ISA to the Deep Ocean Resources Development Co., Ltd. (DORD) and survey cruises have been conducted there.

While contractors perform the environmental survey according to the environmental guidelines of the ISA (ISBA/19/LTC/8; Lodge et al., 2014; Bräger et al., 2018), nodule fauna, which is one of the survey items described in the guidelines, has been gaining interest. Nodule fauna are deep-sea organisms living on the surface of polymetallic nodules distributed on the abyssal seafloor, and there has been a concern that mining activities of manganese nodules leads directly to significant loss of nodule fauna's biodiversity (Veillette et al., 2007a; Vanreusel et al., 2016). Furthermore, Mining Impact of deep-sea Resource Exploitation (MIDAS), a recent research project in the CCZ, indicated that manganese nodules are very important as a fauna habitat and yield biodiversity on the field (Vanreusel et al., 2016). And also the project proposes that areas where nodules are particularly abundant are to be protected (e.g., Gjerde et al., 2016). However, the nodule fauna have not been sufficiently investigated in the CCZ; in particular, a few surveys have been performed in the western part of it (e.g., Veillette et al., 2007a; Veillette et al. 2007b; Gooday et al. 2015; Glover et al., 2016a; Gooday et al., 2018a; Gooday et al., 2018b). For such reason, this paper shows preliminary results of shipboard observations of nodule fauna in the DORD's contract area, which is the western part of the CCZ.

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