38 New Species Discovered at Once — JAMSTEC and Ocean Census Unveil Deep-Sea Biodiversity at Nankai Trough and Shichiyou Seamounts

38 New Species, Unknown Ecosystems — Japan's Deep Sea Still Holds Many Secrets

Japan's ocean harbors an enormous number of organisms still unknown to science. A joint deep-sea survey by JAMSTEC and Ocean Census in 2025 discovered an astonishing 38 new species and 28 candidate new species, dramatically rewriting our understanding of biodiversity in Japanese waters.

Why This Survey Was Conducted

Approximately 240,000 marine species have been described worldwide, but the actual number is estimated at several million. The Ocean Census initiative, launched in 2023, aims to close this massive knowledge gap.

While the Nankai Trough has been extensively surveyed for geological studies related to great earthquakes, biodiversity-focused surveys had rarely been conducted. The Izu-Ogasawara volcanic seamounts were also largely unexplored biologically.

From June 4 to 23, 2025, using the deep-sea submersible support vessel Yokosuka and the manned submersible Shinkai 6500, the team collected baseline biodiversity data across these waters.

Nankai Trough — Unknown Ecosystems at Cold Seep Sites

The Nankai Trough stretches from Suruga Bay to offshore Hyuga-nada, where methane-rich fluids naturally seep from the seafloor at 'cold seep sites.'

Previously, only 14 species had been reported from Nankai Trough cold seeps. This survey discovered approximately 80 species across five methane seep sites at depths from 600m to 4,600m — a dramatic expansion from 14 to 80 species.

Breakdown of Discovered Organisms

• Mollusks (snails, bivalves, etc.): 33 species
• Annelids (polychaete worms, etc.): 23 species
• Arthropods (crabs, shrimp, amphipods, etc.): 11 species
• Ribbon worms: 5 species
• Echinoderms (starfish, brittle stars, sea cucumbers, etc.): 4 species
• Cnidarians (hydrozoans, zoanthids, etc.): 3 species
• Bryozoans: 1 species

At each survey site, 15–30 species were newly confirmed where previous records showed only 1–6 species. The Nankai Trough is proving to be one of the most biologically rich regions in Japanese waters.

Shichiyou Seamounts — Vibrant Ecosystems on Unexplored Seamounts

The Shichiyou Seamounts are a chain of volcanic seamounts located 500–700 km southeast of Tokyo, named after days of the week: Sunday, Monday, Tuesday, and Friday Seamounts. This survey documented deep-sea coral gardens, sponge communities, and diverse fauna for the first time.

Notable discoveries include two new species of polychaetes symbiotic with glass sponges, five new species of squat lobsters, and additional new species of octocorals, ribbon worms, amphipods, and kinorhynchs.

What Shinkai 6500 Made Possible

The manned submersible Shinkai 6500 proved its strengths in this expedition. Having biologists directly observe and carefully sample in the deep-sea environment maximized the scientific value of limited dive opportunities.

Having multiple biologists specializing in different taxonomic groups observe and collect using diverse methods at the same site proved to yield a far greater diversity of organisms.

— JAMSTEC Press Release

2025年9月から10月にかけて、国内外の専門家がJAMSTECに集まりワークショップを開催。採集された528ロット以上の標本を精査した結果、新種38種と新種の可能性が高い28種が確認されました。これらの成果は学術論文として取りまとめられるとともに、「Ocean Census生物多様性プラットフォーム」を通じて一般に公開される予定です。

For marine biodiversity threats, see "EuroWorm Project vs Silent Extinction."

編集部の解説

14種から80種へ — 「調べていなかっただけ」という衝撃

南海トラフの冷湧水域でこれまで報告されていた生物はたった14種でした。今回の調査で一気に80種が確認されたということは、過去の記録が「少なかった」のではなく、そもそも「調べていなかった」ことを意味します。地震研究で注目されてきた南海トラフに、これほど豊かな化学合成生態系が広がっていたことは、日本の深海研究にとって大きな転換点です。

曜日の名を持つ海山 — ロマンあふれる未踏の世界

日曜海山、月曜海山、火曜海山、金曜海山——名前だけは付けられていたものの、深海の生物調査が一度も行われていなかった海山群。そこにガラス海綿の群集やコシオリエビの新種5種など、驚くべき多様性が眠っていました。地理的に隔離された海山は独自の進化が進みやすく、固有種の宝庫となる可能性を秘めています。

海底資源開発時代に不可欠な「影響を受ける前」の記録

メタンハイドレートの開発や洋上風力発電など、今後の人類活動は深海にも及びます。今回の調査で得られた生物多様性のベースラインデータは、開発による環境影響を評価するための比較基準となります。「何がそこにいたのか」を知らなければ、「何が失われたのか」も分かりません。科学的な記録を残すことの重要性を改めて感じさせる研究成果です。