The Groundbreaking JAMSTEC-Ocean Census Expedition

In June 2025, a collaborative effort between Japan's Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and the Nippon Foundation-Nekton Ocean Census launched a pioneering deep-sea expedition aboard the research vessel Yokosuka, supported by the world-renowned manned submersible Shinkai 6500. This mission targeted two under-explored regions within Japan's Exclusive Economic Zone: the geologically active Nankai Trough, approximately 500-600 km southwest of Tokyo, and the remote Shichiyo Seamount Chain, 500-700 km southeast of Tokyo. Over 20 days from June 4 to 23, the team collected more than 528 biological specimens from depths ranging from 600 to 4,600 meters, setting the stage for remarkable biodiversity revelations.

The expedition's success underscores JAMSTEC's pivotal role in advancing marine science, often in partnership with leading Japanese universities. These institutions provide essential academic expertise, from taxonomy to molecular analysis, highlighting the synergy between government research agencies and higher education in Japan.

Revolutionary Findings in the Nankai Trough Methane Seeps

The Nankai Trough, a subduction zone known for methane seeps and earthquake risks, proved to be a biodiversity hotspot. Prior surveys documented only 14 species, but this expedition identified 80 seep-associated animals—a five-fold increase. These included 33 mollusks such as snails, clams, and glisten-worms; 23 annelids like lugworms; 11 arthropods including crabs, shrimp, and amphipods; five nemerteans (ribbon worms); four echinoderms (sea stars, brittle stars, sea cucumbers); three cnidarians (zooanthids, anemones, hydroids); and one bryozoan.

This surge in documented fauna reveals complex ecosystems sustained by chemosynthesis, where microbes convert methane into energy, supporting diverse life forms independent of sunlight. Such discoveries emphasize the need for baseline data amid potential resource extraction like methane hydrates.

Shichiyo Seamount Chain: Isolated Ecosystems and Symbiotic Wonders

The Shichiyo Seamount Chain, comprising submerged volcanic peaks like Nichiyo, Getsuyo, Kayo, and Kin'yo, yielded vibrant coral gardens and sponge-dominated seafloors. Highlights include five new squat lobster species from the genus Munidopsis and numerous first records for Japan, such as octocorals, nemerteans, amphipods, gastropods, and kinorhynchs.

Particularly captivating were the 'glass castles'—hexactinellid glass sponges housing symbiotic polychaete worms. Two new species, Dalhousiella yabukii and Leocratides watanabeae, coexist within these fragile structures, showcasing convergent evolution in sponge-dwelling lifestyles. These findings illustrate the seamounts' role as evolutionary cradles, isolated by deep waters.

Spotlight on the Newly Described Species

Taxonomic experts confirmed 38 new species, with 28 more candidates pending. Notable examples:

• Squat lobsters (Munidopsis spp.): Five deep-sea variants adapted to seamount pressures.
• Polychaete worms: Dalhousiella yabukii and Leocratides watanabeae, thriving symbiotically in glass sponges.
• Mollusks and annelids: Diverse seep dwellers expanding known distributions.
• Arthropods: Crabs and amphipods in novel associations.

These species enrich Japan's marine inventory, many preserved for DNA barcoding on the Ocean Census platform.

Academic Powerhouses Driving the Research

The expedition drew talent from top Japanese universities collaborating with JAMSTEC. Key contributors included:

• Nagoya University: Naoto Mikami on polychaete taxonomy.
• Hokkaido University: Yoshitaka Shiraki, expertise in deep-sea ecology.
• University of Tokyo: Kento Oka and Moe Sato, molecular analysis.
• Ryukyu University: James Reimer, cnidarian specialist.
• Kobe University: Tadashi Kobayashi.
• Kagoshima University: Yuka Kushida.
• Hiroshima Shudo University: Masanori Okanishi.
• Kitasato University: Tsuyoshi Nagaoka.

These partnerships exemplify how Japan's higher education fuels national research, training PhD students and postdocs in cutting-edge oceanography. For aspiring marine biologists, programs at these institutions offer pathways to fieldwork on vessels like Yokosuka.

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Photo by Sandy Ravaloniaina on Unsplash

Key Publications Cementing the Discoveries

Results appeared in peer-reviewed journals:

• Ecosphere (2025): "Biological surveys reveal unexpectedly high faunal diversity at Nankai Trough methane seeps" by Chong Chen et al. Details the 80-species baseline.Read the study
• Zoological Journal of the Linnean Society: "Single origin and convergent host use of hexactinellid sponge symbiosis in Hesionidae" by Naoto Jimi et al. Describes the glass sponge worms.Access the paper

More papers are forthcoming, with data on the Ocean Census platform.

Technological Innovations Powering Deep-Sea Exploration

Shinkai 6500, JAMSTEC's flagship submersible, reached 6,500m, enabling precise sampling. Advanced imaging and ROVs captured high-res footage, vital for taxonomy. Universities like the University of Tokyo contribute to submersible tech development, fostering interdisciplinary marine engineering programs.

Conservation Challenges and Policy Implications

Discoveries highlight vulnerabilities: Nankai Trough faces seismic risks and hydrate mining; seamounts, trawling. JAMSTEC advocates marine protected areas. Japanese universities lead impact studies, informing policy via government reports.

Japan's Preeminence in Global Oceanography

JAMSTEC, with university ties, positions Japan as a leader. Collaborations with Tohoku University (WPI-AIMEC) advance ecosystem modeling. Oceanography degrees at Hokkaido, Tokyo, and Kyushu Universities attract global talent, boosting research output.

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Career Pathways in Deep-Sea Marine Science

Japan's marine sector offers postdocs, faculty positions at JAMSTEC-partnered unis. Roles in taxonomy, genomics, submersible ops abound. Research assistant jobs and postdoc opportunities proliferate, with English-friendly programs.

• PhD in Marine Biology: U Tokyo, Hokkaido U.
• Technical Staff: JAMSTEC vessels.
• Professorships: Focus on biodiversity.

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Photo by William Pickard on Unsplash

Looking Ahead: Future Expeditions and Legacy

Upcoming JAMSTEC-D-ARK cave surveys and Ocean Census phases promise more finds. Data sharing accelerates global science, inspiring Japanese students. These efforts safeguard oceans, blending research with conservation.

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