The hadal zone – ocean trenches from ~6,000 m to nearly 11,000 m deep – contains extensive hard substrates along trench walls, fracture zones, and subducted seamounts. Because recovering rock samples from such depths is extremely challenging, the fauna inhabiting these hard surfaces has remained largely unknown. Now, a team led by the Institute of Deep‑Sea Science and Engineering (IDSSE), Chinese Academy of Sciences, under the Global Hadal Exploration Programme (GHEP), has discovered a protist‑dominated hard‑substrate fauna in seven hadal regions around Oceania.

The findings are published in Science on 14 May 2026.

The fauna comprises 32 species across six phyla, most new to science, including one new family of monothalamous foraminifera (Plumettidae) and one new bryozoan family (Pierrellidae). The organisms are millimetre‑sized and reach densities up to 4,300 individuals per dm². The study shows that the dominant, filamentous“mysterious” life forms are agglutinated foraminifera, which the researchers refer to “rock feathers” or “shirong” in Chinese.

For years, their biological affinity puzzled scientists because the individuals are small, morphologically simple, and contain abundant sediment particles that complicate DNA extraction and sequencing. Across all hard‑substrate dives, no typical chemosynthetic indicator taxa (e.g., siboglinid tubeworms or vesicomyid clams) were observed. Metagenomic and metabarcoding analyses detected no known chemolithoautotrophic symbionts in the dominant species. Instead, terrestrial pine pollen grains, many at various stages of digestion, were found inside several species, confirming a heterotrophic diet and challenging the earlier chemolithoautotrophic hypothesis.

Using in situ seafloor imagery and samples from 98 dives of the manned submersible Fendouze, the researchers documented that this protist‑dominated fauna is widely distributed across seven hadal regions around Oceania, especially at 9,000–10,898 m in the Kermadec and Mariana trenches. Based on other recent GHEP cruises in the last three years, the same fauna also occurs in five other trenches (Aleutian, Kuril–Kamchatka, Puysegur, Atacama, and Mussau), suggesting that such assemblages may be prevalent in hadal trenches globally. The living biomass carbon contributed by these sessile foraminifera is estimated to account for 2–11% of the total eukaryotic biomass carbon in global hadal trenches, indicating a previously overlooked but highly active carbon “hotspot” that provides critical new insights for deep‑sea carbon cycle research and reassessment of hadal biological pump efficiency.

The study also extends the maximum depth limits of several marine animal groups: the deepest known bryozoan (9,981 m, Pierrella fendouzhei sp. nov.), scyphozoan polyps (9,982 m), and hydrozoan polyps (9,195 m). The deepest bryozoan belongs to an ancient lineage first described from Cretaceous shallow‑water strata, suggesting that the hadal zone may act as a refuge for archaic taxa. The V‑shaped topography of trenches funnels organic matter downslope toward the axis, and turbidity currents frequently scour rock surfaces. In response, these agglutinated foraminifera mainly colonise vertical lateral surfaces of rock outcrops, where the impact of turbidity currents is somewhat reduced, with their bodies hanging downward from the attachment point. This hanging- downward posture is interpreted as a strategy to avoid burial by sediment and to efficiently capture organic particles in upslope‑moving currents. The biodiversity, biogeography, functional ecology, and global carbon‑cycle role of these deep hard‑substrate faunas remain open for further investigation.

Authors and affiliations

The first author is Dr Xikun Song (Associate Researcher, IDSSE), and the corresponding author is Dr Xiaotong Peng (Professor, IDSSE). The collaborating institutions include Earth Science New Zealand, National Oceanography Centre (UK), Natural History Museum (UK), Bavarian State Collection of Zoology (Germany), University of Vienna (Austria), National Research and Innovation Agency (Indonesia), Tsinghua University, Xiamen University, and Institute of Software Chinese Academy of Sciences.

Funding

This work was supported by the National Key Research and Development Program of China (2022YFC2805400, 2025YFE0214500), National Natural Science Foundation of China (42276090), International Partnership Program of the Chinese Academy of Sciences (183446KYSB20210002), Hainan Province Science and Technology Special Fund (DSTIC‑GXHC: 2022003, 2024001), the project of IDSSE (E371020101), and the Global Trench Exploration and Diving Programme (Global TREnD).

About Global Hadal Exploration Programme (GHEP)

GHEP is a ten‑year United Nations Ocean Decade programme initiated and conducted by IDSSE, dedicated to exploring the deepest parts of the global ocean. It was formerly known as the “Global Trench Diving and Exploration Programme” (Global TREnD). The programme uses full‑ocean‑depth submersible technology (e.g., Fendouze) to conduct scientific research on hadal geology, life, and environment.

Fig. 1 Maps of 98 manned submersible dive sites in seven hadal regions around Oceania.

Fig. 2. Overview of dominant species of the deepest hard-substrate fauna in the Kermadec and Mariana trenches.