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

[MZZ42-P06] Metabarcoding Analysis of Eukaryotic Diversity in the Seamounts in the Northwest Pacific

*Tomo Kitahashi¹, Miyuki Nishijima², Akira Iguchi², Shunsuke Kondo¹, Atsushi Suzuki² (1. KANSO TECHNOS Co., Ltd., 2.National Institute of Advanced Industrial Science and Technology)

Keywords:Metabarcoding analysis, Cobalt-rich crust, Eukaryote, Meiobenthos

Cobalt-rich crusts, abundant in cobalt, nickel, manganese and other elements, are distributed across seamounts scattered on the seafloor in the Northwest Pacific Ocean. Recently, attention has been drawn to the exploration and extraction of these seabed resources, with increasing concern about the potential environmental impacts. The International Seabed Authority (ISA), which oversees the exploration and development of seabed resources in the high seas, has established environmental guidelines to minimize the impact of resource extraction. It highlights benthic organisms, including meiobenthos, as one of the key environmental survey targets (ISBA/25/LTC/6/Rev.3). However, in the low-latitude, low-productivity regions where cobalt-rich crusts are found, the density of meiobenthos is low compared to larger organisms, making it challenging to obtain enough specimens for statistical analysis. Moreover, the identification of individual organisms is dependent on microscopic examination, making the analysis time-consuming. Recently, metabarcoding techniques targeting environmental DNA have been employed for the analysis of deep-sea biodiversity. Kitahashi et al. (2020) revealed that metabarcoding analysis could more accurately capture the spatial variation in community structure compared to microscopic analysis in a seamount (JA06) within a Japanese mining area.
In this study, we conducted metabarcoding analyses on four seamounts (JA03, JA04, JA06, and JA17) within a Japanese mining area, aiming to analyze the variations in community structures between different seamounts and topographic features. The analysis assigned 1,360,707 reads and 6,982 ASVs (amplicon sequence variants) to eukaryotes, including meiobenthos. The comparison of ASV numbers revealed a higher count on the flat-top than at the base of the JA17 seamount, but the statistical analysis was not feasible due to the single sampling station at the base. Moreover, although not statistically significant, the JA17 seamount exhibited a greater number of ASVs on its flat-top compared to the other seamounts (Fig. 1). This result aligns with the general principle of the latitudinal gradient of biodiversity, which posits an increase in diversity from the equator towards the poles. Multivariate analyses of eukaryotic community structures showed significant differences between seamounts (PERMANOVA, p<0.01). To visualize variations in community structures, we conducted a Principal Coordinate Analysis (PCoA) (Fig. 2). The results showed distinct community structures on the flat-tops of JA06 and JA17 seamounts, while their bases showed similar structures. Despite their geographical proximity, the community structures on the flat-tops of JA03 and JA04 seamounts differed. The community structures at the flat-top and base of the JA03 seamount were similar. These findings suggest that while distinct communities exist on the flat-tops of seamounts, the communities at the base share similarities.