The Cosmonaut Sea is an under-studied area and a “white spot” for macrobenthos research. Here, we report on the species diversity and community structure of macrobenthos collected using tringle trawls on the 38th Chinese National Antarctic Research Expedition (CHINARE) in the Cosmonaut Sea, East Antarctica. A total of 11 tringle trawls were deployed at different depths across the shelf, slope and seamount of the Cosmonaut Sea. A total of 275 macrobenthic species were found from 207 to 1994 m. The species richness per station varied from 23 to 89. Echinoderms (100 species), arthropods (48 species) and mollusks (36 species) were the most dominant groups. Echinoderms and arthropods dominated in abundance at seamount stations, and echinoderms, arthropods and polychaetes dominated in abundance at slope stations, while bryozoans, corals, ascidians and sponges were abundant on the Cosmonaut Sea shelf. Depth was the major driving force influencing the distribution of macrobenthos. The main components were two core communities. One was dominated by sessile suspension feeders and associated fauna. Variants of this community include sponges and bryozoans. The other core community was dominated by mobile deposit feeders, infauna and grazers–epifauna, which included arthropods and echinoderms. The results showed that the slope (40–50° E, 65–67° S) of the Cosmonaut Sea may be an important area with complex ecological processes. The results of this study contribute to the knowledge of species diversity and communities of macrobenthos in the Cosmonaut Sea and provide monitoring data for future ecosystem health assessments and better protection.

A free-fall baited camera lander was launched for the first time on the Cosmonaut Sea shelf of East Antarctica at a depth of 694 m during the 38th Chinese National Antarctic Research Expedition (CHINARE) in 2022. We identified 31 unique taxa (23 were invertebrates and eight were fish) belonging to eight phyla from 2403 pictures and 40 videos. The Antarctic jonasfish (Notolepis coatsi) was the most frequently observed fish taxa. Ten species of vulnerable marine ecosystem (VME) taxa were observed, accounting for 32% of all species. The maximum number (MaxN) of Natatolana meridionalis individuals per image frame was ten, and they were attracted to the bait. The macrobenthic community type were sessile suspension feeders with associated fauna (SSFA), which was shaped by the muddy substrata with scattered rocks. Rocks served as the best habitats for sessile fauna. The study reveals the megafauna community and their habitat by image survey in the Cosmonaut Sea for the first time. It helped us obtain Antarctic biodiversity baselines and monitoring data for future ecosystem health assessment and better protection.

A free-fall baited camera lander was launched for the first time on the Cosmonaut Sea shelf of East Antarctica at the depth of 694 m during the 38th Chinese National Antarctic Research Expedition (CHINARE) in 2022. We identified 31 unique taxa (23 of invertebrates and 8 of fishes) belonging to 8 phyla from 2403 pictures and 40 videos. The Antarctic jonasfish (Notolepis coatsi) was the most frequently observed fish taxa. Ten species of vulnerable marine ecosystem (VME) taxa were observed, accounting for 32% of all species. The maximum number (MaxN) of Natatolana meridionalis individuals per image frame was ten, and they were attracted to the bait. The macrobenthic community type was sessile suspension feeders with associated fauna (SSFA), which was shaped by the muddy substrata with scattered rocks. Rocks served as the best habitats for sessile fauna. The study reveals the megafauna community and their habitat by image survey in the Cosmonaut Sea for the first time. It helped us obtain Antarctic biodiversity baselines and monitoring data for future’s ecosystem health assessment and better protection.

Two new marine nematode species of the genus Sabatieria and a new record of Hopperia beaglense Chen & Vincx, 1998 belonging to the family Comesomatidae are described from the Southern Ocean using morphological and molecular data. Sabatieria cosmonautaesp. nov. is characterized by body length 1786–2230 μm, short cephalic setae, lateral differentiation of body cuticle with sparse punctations starting from amphid to near tail tip, spiral amphidial fovea with three turns, spicules arcuate and 1.2–1.5 cloacal body diameters long, with straight dorso-caudal gubernacular apophyses, and 16 or 17 precloacal supplements. Sabatieria crassilongasp. nov. is characterized by body length 2628–3613 μm, short cephalic setae, cuticle with lateral differentiation of coarser and irregularly spaced punctations extending from anterior edge of amphid to the tail region, amphidial fovea spiral with 2.5 turns, males with spicules 1.2–1.5 cloacal body diameters long, gubernaculum with a long straight dorso-caudal apophysis, and 20 or 21 fine precloacal supplements. Hopperia beaglense, which was originally described from the Strait of Magellan and the Beagle Channel, is recorded from the Southern Ocean for the first time. Phylogenetic analysis based on concatenated 18S + 28S rRNA sequences places the two new species and the new record within Comesomatidae. The tree topology shows Comesomatidae forming a well-supported monophyletic clade, whereas the genus Sabatieria is not monophyletic.