Protist-dominated hard substrate faunas thrive at the deepest ocean depths

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Abstract
Deep-sea hard substrates host faunal novelties and distinct evolutionary lineages. However, sessile organisms on rocks are difficult to sample and largely unknown at extreme hadal depths. Here, we report a deep hard-substrate fauna (9000 to 10,898 meters), comprising 32 species of six protist and metazoan phyla, most millimeter-sized and new to science, from the Kermadec and Mariana trenches, using the manned submersible Fendouzhe . We show that the filamentous organisms dominating these assemblages are heterotrophic foraminiferans, challenging the earlier chemolithoautotrophic hypothesis. Large-scale seafloor imaging and sampling suggest that similar protistan-dominated sessile communities thrive in seven hadal regions around Oceania. These faunas open new perspectives on biodiversity at the deepest ocean depths and unveil widespread, but previously unrecognized, carbon hotspots in global hadal trenches.
Funding Information
  • National Natural Science Foundation of China (42276090)
  • Chinese Academy of Sciences (183446KYSB20210002)
  • National Key Research and Development Program of China (2022YFC2805400)
  • National Key Research and Development Program of China (2025YFE0214500)
  • Hainan Provincial Department of Science and Technology (DSTIC-GXHC-2022003)
  • Global Trench Exploration and Diving Programme (N/A)
  • Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences (E371020101)
  • Hainan Province Science and Technology Special Fund DSTIC GXHC (2022003)
  • Hainan Province Science and Technology Special Fund DSTIC GXHC (2024001)

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