Daniel Leduc

Whale falls are biodiversity oases at seabeds^1,2,3,4,5,6, yet their record from the oceans has remained sparse and fragmentary^6,7. Here we report the discovery of a vast whale necropolis in the Diamantina Zone (4,616- to 7,001-m depth), extending about 1,200 km along the sea floor of the southeastern Indian Ocean. This area has a deep and extensive accumulation comprising five modern natural whale-fall communities and 476 fossil cetaceans recorded. We show that carcasses host specialized communities dominated by brittle stars, bone-boring worms and chemosynthesis-based bivalves and that the fossil record in this area comprises both extant and extinct deep-diving beaked whales. Isotopic dating shows that whale falls in this region have occurred since at least 5.3 million years ago. These findings reshape the understanding of the limits and biogeography of whale-fall ecosystems and establish some deep sea floors as a fossil archive for tracing cetacean evolution over geological time.

The mostly marine nematode order Desmoscolecida is globally distributed with over 270 species known to date. Here, we describe Greeffiella bellula n. sp., the first desmoscolecid species to be described from New Zealand waters, from deep‐sea sediments. The new species is most similar to G. japonica , described from coastal sediments in the Sea of Japan, in having relatively few (Greeffiella bellula n. sp. can be most easily differentiated from the latter by the different body shape and in having fewer pairs of subdorsal setae. A dichotomous key to the 15 valid species of the genus is presented. Results of SSU phylogenetic analyses based on 19 Desmoscolecidae sequences confirmed the genus assignment of the new species, but unlike previous analyses did not provide support for the monophyly of the subfamilies Desmoscolecinae and Tricominae, or of the closely related genus Desmoscolex .

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.

Deep-ocean Assessment and Reporting of Tsunami (DART) buoys are deployed across the Southwest Pacific and provide substrates for biofouling communities. Two new free-living nematode species, Atrochromadora tereroa sp. nov. and Euchromadora rebeccae sp. nov. (family Chromadoridae), and one known species, Halomonhystera refringens (Bresslau & Schuurmans Stekhoven, 1933) comb. nov. (family Monhysteridae), are described from buoys deployed off Raoul Island in the Kermadec/Rangitāhua region and off New Zealand’s East Cape. Thalassomonhystera refringens (Bresslau & Schuurmans Stekhoven, 1933) Jacobs, 1987 and T. anoxybiotica (Jensen, 1986) Jacobs, 1987 are transferred to Halomonhystera based on the presence of precloacal and caudal papillae in males. In addition, Halomohystera zhangi Li, Huang & Huang, 2024 is synonymised with Halomonhystera refringens. Updated keys to Atrochromadora, Euchromadora and Halomonhystera species are provided. The presence of nematodes on buoys located more than 100 km from the nearest landmass and in deep waters (>3,500 m water depth) shows that some nematode species are capable long-distance dispersal to colonise new substrates. Such dispersal by Atrochromadora, Euchromadora and Halomonhystera species likely occurs via drifting macroalgal fragments.

Seafloor mineral resources offer a potential novel source of critical metals ^1,2 . However, uncertainty about the potential impacts of deep-sea mining on marine ecosystems has led to increasing calls for a scientifically rigorous framework to assess environmental effects ^3–6 . Here, we provide a framework for the first integrated ecosystem assessment of the Clarion-Clipperton Zone (CCZ) — a region of the equatorial Pacific with 17 active exploration areas for potential mining of seafloor polymetallic nodules (totalling ~1.2 million km ² ). We present a comprehensive model of ecosystem structure in the CCZ, extending from the ocean surface down to the abyssal seafloor (~3,500–5,500 m depth), to identify the potential impacts of mining activities on ecosystem components, functions, and services. Our assessment shows that adverse effects could occur within and proximal to directly mined areas, including sustained changes in seafloor communities due to substrate removal and sediment redeposition. However, our analysis did not identify any functional pathways that could transmit effects from the abyssal seafloor to the upper ocean. We identify ecosystem indicators to assess the impacts of a prototype mining system, informing the development of environmental management and monitoring plans before the potential onset of industrial-scale mining in the deep sea.

Three new species of selachinematid nematodes, Choanolaimus serieporus sp. nov., C. sparsiporus sp. nov. and Gammanema lunatum sp. nov., are described from the continental slope of New Zealand. We also provide partial ribosomal DNA SSU and LSU D2–D3 sequences for Gammanema lunatum sp. nov. and another selachinematid species, Halichoanolaimus funestus Leduc, 2020. Until now, the genus Choanolaimus de Man, 1880 comprised a single species restricted to coastal dunes, beaches and estuarine environments of the North Sea, Northeast Atlantic and Northeast Pacific. To our knowledge, the present study provides the first record of the genus from the southern hemisphere and from the deep-sea environment (> 250 m depth). The two new species of Choanolaimus are characterised by two longitudinal dorsosublateral rows of pore complexes, which differ in arrangement between species thus providing a taxonomically informative character. The presence of pore complexes in Choanolaimus is consistent with previous findings, which show that within the Selachinematidae Cobb, 1915, pore complexes are only found in genera with a blind intestine. The two species of Gammanema Cobb, 1920 known so far from New Zealand share characters not found in any other species of the genus, i.e., loop-shaped amphids in males and the presence of cuticle spines, which indicates that these two species may have evolved from a common ancestor. The SSU and LSU D2–D3 consensus trees are largely congruent. Our molecular phylogenetic analyses confirm previous results, which support the monophyly of the family Selachinematidae but not of the subfamilies Selachinematinae and Choniolaiminae, with some genera placed in different clades despite sharing strong morphological similarities. We have found no support for the monophyly of the genus Halichoanolaimus de Man, 1886, which forms a well-supported clade with the genera Bendiella Leduc, 2013, Cobbionema Filipjev, 1922 and Demonema Cobb, 1894.

Little is known about the diversity of free-living nematodes of New Zealand’s continental shelf environments. A preliminary analysis of samples obtained from the continental shelf along the east coast of New Zealand’s North Island revealed the presence of eleven previously described species, which are recorded from this region of New Zealand for the first time. Two of these species were originally described from intertidal sediments, two were described from subtidal or continental shelf environments (5–40 m depth), and seven were originally described from the continental slope (ca 400–1250 m depth). A further three new species, Psammonema buamphida sp. nov., Paramonohystera spinosipsicula sp. nov. and Sabatieria pararticulata sp. nov. are described. Sabatieria pararticulata sp. nov., shares the unusual feature for the genus of having long, jointed spicules with S. articulata Fu, Leduc & Zhao, 2019, which was also described from New Zealand. The presence of this feature, which is otherwise absent in all other species of the genus, in the two New Zealand species suggests that S. articulata and S. pararticulata sp. nov. likely evolved from a common ancestor.

Anthropogenic impacts are increasingly affecting deep‐sea environments, including seafloor sediment disturbances by bottom trawling and seafloor mining. Fieldwork in the ‘Resilience Of Benthic Ecosystems to Sedimentation’ (ROBES) project were conducted in 2018–2020 on the 400 m‐deep Chatham Rise crest, eastern Aotearoa New Zealand. Water column turbidity data, sediment traps on near‐seabed moorings and benthic landers and surficial sediments from multi‐corers provided baseline and post‐impact information following an artificially induced seafloor disturbance event in June 2019 using a modified harrow plough in and around an elongated bathymetric depression, designated as the ‘Butterknife’. During the disturbance, total mass and particulate organic carbon (POC) near‐bed fluxes were elevated above long‐term fluxes (2018–20). Long‐term 2018–19 fluxes were generally less than in 2019–20, driven by interannual oceanographic variations. These results, coupled with 50–100 m‐thick benthic boundary layers, suggest that lateral advection is a dominant process in the resuspension and redistribution of seafloor sediments on the rise. Further research is required to better understand the longer term dynamics of particle transport and deposition in response to human activities, such as bottom trawling or proposed phosphorite seafloor mining, especially in bathyal environments, such as the Chatham Rise.