Hadal trenches, some of the Earth's least explored and understood environments, have long been proposed to harbour chemosynthesis-based communities1,2. Despite increasing attention, actual documentation of such communities has been exceptionally rare3,4. Here we report the discovery of the deepest and the most extensive chemosynthesis-based communities known to exist on Earth during an expedition to the Kuril-Kamchatka Trench and the western Aleutian Trench using the manned submersible Fendouzhe. The communities dominated by siboglinid Polychaeta and Bivalvia span a distance of 2,500 km at depths from 5,800 m to 9,533 m. These communities are sustained by hydrogen sulfide-rich and methane-rich fluids that are transported along faults traversing deep sediment layers in trenches, where methane is produced microbially from deposited organic matter, as indicated by isotopic analysis. Given geological similarities with other hadal trenches, such chemosynthesis-based communities might be more widespread than previously anticipated. These findings challenge current models of life at extreme limits and carbon cycling in the deep ocean.

A new species of meiobenthic sipunculan, Phascolion kamchatikus sp. nov. collected from coarse sand and shell hash in shallow waters in the northwestern Pacific, is described and illustrated using light and electron microscopy. This new species is well distinguished from all other congeners by a unique combination of main taxonomic characters. This is the only sipunculan having only two primary tentacles in both juvenile and sexually mature worms. There are no hooks and holdfast papillae in the adult stages. Because of the presence of three nearly equal in size retractor muscles forming a retractor column divided for most of its length, this species is assigned to the subgenus Isomya of the genus Phascolion. Unlike most other species of the genus Phascolion, P. kamchatikus sp. nov. has an interstitial mode of life moving among the coarse sand grains and shell hash accumulated between rocks and stones in shallow water areas alongside the Pacific coast of Kamchatka, Aleutian Islands and Alaska Peninsula. Phascolion kamchatikus sp. nov. constitutes the only third interstitial species of the phylum Sipuncula. This is also the ninth species of Phascolion in the northwestern Pacific and the first interstitial representative of this genus in the Pacific Ocean.

Seamounts and oceanic currents play crucial roles in shaping the genetic diversity of species by either acting as barriers or pathways for species dispersal. In the meiofaunal samples collected using ROV facilities at the slope of the Koko Guyot (2172 m) in the southernmost part of the Emperor Seamount Chain in the Northwestern Pacific, we found representatives of three kinorhynch genera, Echinoderes cf. lupherorum S & oslash;rensen et al. 2018, Campyloderes cf. vanhoeffeni Zelinka, 1913 and Sphenoderes sp. 1., previously known from other locations in the Pacific. Kinorhynchs were studied and illustrated using light (LM) and scanning electron (SEM) microscopy to prove the species identity and to compare morphological variations with representatives of these species collected from other, very distant localities in the Pacific. We illustrate the pan-oceanic distribution of the collected species with a system of abyssal currents in the Pacific. The probable distribution pattern corresponds with the northward pathway of Antarctic Bottom Water out of the Southern Ocean in the Pacific through the deep-sea area off New Zealand. Echinoderes lupherorum appears to be the first representative of the Echinoderidae with the pan-Pacific distribution. Discussions on the biogeography of Campyloderes cf. vanhoeffeni Zelinka, 1913 and Sphenoderes in the Pacific are also provided.

Taxonomic studies of the phylum Kinorhyncha follow a standardised structure, which is extremely useful in many aspects, such as making it easier to read and compare the different species descriptions. Nevertheless, the morphological measurements methods, essential for formal description of species, may differ according to the authors. In the present contribution, we propose a standardised method of taking and representing the measurements, with the aim of obtaining comparable and repeatable morphometric results. Additionally, we propose an online repository to make the measurements accessible to all researchers in the same format, facilitating future comparisons and studies. Finally, a glossary that compiles and defines all the measurements that may be included in Kinorhyncha descriptions is presented.

Benthic communities of the hydrothermally active submarine Piip Volcano (55 degrees 445 N, 167 degrees 263 E, 368-495 m, the southwestern Bering Sea) were explored during the 75th and 82nd cruises of the RV Akademik M.A. Lavrentyev using the ROV Comanche 18. The Piip Volcano is the northernmost hydrothermal region in the Pacific. Macrofauna composition and community structure were investigated based on qualitative and relative abundance samples along with still images and video records. In total, 130 species of macro- and megafauna were found, of which similar to 25% are new to science. Of the fauna, 9 species (7%) are obligate or potentially obligate to environments with access to reduced chemicals. These species are the bivalve Calyptogena pacifica (Vesicomyidae: Pliocardiinae), the gastropods Parvaplustrum wareni (Parvaplustridae) and Provanna sp. (Provannidae), the amphipod Onesimoides sp. (Tryphosidae), the leptostracan Nebalia piipensis (Nebaliidae), the isopod Eurycope andreyi (Munnopsidae), and the polychaetes Neosabellides uschakovi (Ampharetidae), Ophryotrocha beringiana (Dorvilleidae) and Harmothoe globosa (Polynoidae). The total species richness of the Northern and Southern summits was almost identical (90 species and 85 spp respectively), but the number of species on sites without bacterial mats on the Northern Summit (81 spp) was almost 1.5 times higher than on the Southern Summit (57 spp). At the same time the species richness was almost twice higher in habitats with bacterial mats and/or clam beds on the Southern Summit (58 spp) compared to the Northern one (32 spp). The main faunal difference was the absence of Calyptogena pacifica on the Northern Summit. The factors that may explain differences of the faunal communities of the Northern and Southern summits are discussed. The distinctive features of macro- and megafaunal communities of the Piip Volcano were the significant number of taxa, obligate for reducing habitats, of different taxonomic levels including family and subfamily levels and plentiful abundances of sedentary organisms, including the sea anemone Corallimorphus cf. pilatus, the demosponge Vulcanella koltuni, calcareous sponges and benthopelagic Trachimedusa, all of them presumably utilizing the rich food resources of reducing habitats.

Modern problems of the investigation of marine biodiversity and bio-resources and their inventory in the deep-sea of the World Ocean are considered. The discussion of these problems is also based on the data of aseries of deep-water marine expeditions of the National Scientific Center of Marine Biology of the Far Eastern Branch of the Russian Academy of Sciences (NSCMB FEB RAS) in the deepest areas of the Far Eastern Seas and adjacent waters of the North-West Pacific. New results of a series of the deep-sea expeditions within the special RAS Project “Fundamental problems of investigation and conservation of the deep-sea ecosystems in the potentially ore-reach areas in the North-West Pacific” are briefly introduced and discussed (project of RAS № 3.1902.21.0012). Several “unique” deep-sea ecosystems found in the ore bearing sites and the active fishing areas in the North-West Pacific are described. Some safety opportunities for these “unique” ecosystems and possible limitations in the use of dangerous mining and fishing techniques disturbing deep-sea landscapes are considered, including various conservation statuses.

Methane seep communities on the Koryak slope in the Bering Sea were discovered in 2018 during the 82nd cruise of the RV Akademik M.A. Lavrentyev using ROV Comanche 18. Methane seeps found between 400 m and 695 m depth are the northernmost chemosynthesis-based habitats (similar to 61 degrees N) known to date in the Pacific. Macrofauna species composition and community structure of methane seep and background benthic communities were investigated at three depth horizons: 400-402 m, 417-429 m and 647-695 m. A total of 335 macrofaunal species were identified. At the depth 647-695 m the species richness in the methane seep communities was 265 species and 72 species in the background. The deepest seep communities were characterized by the highest species richness, relatively high evenness and strong variations in the composition and structure. At shallower depths the species richness was low: 33-34 species at methane seeps and 66-71 in the background. The methane seep communities at shallow depths showed relatively low evenness and low diversity of community structure. The highest species richness at the greatest depth can be related in part to increased habitat heterogeneity associated with carbonate crusts and vesicomyid clam beds occurring only at deeper methane seeps. The deepest methane seep communities were dominated by the chemosymbiotrophic pliocardiine Calyptogena pacifica; dominant in the background was the ophiumid Ophiophthalmus normani. At shallower methane seeps only single specimens of C. pacifica were found. The shallower methane seeps were dominated by the background species despite numerous extensive bacterial mats and high potential toxicity of the environment. The seep community at 417-429 m was dominated by the echinoid Brisaster latifrons with population density on the bacterial mat four times higher than in the background. Four chemosymbiotrophic species were recorded at 647-695 m and only one was found at shallower depths. Potentially obligate to reducing habitats polychaetes of the genus Neosabellides and Ophryotrocha occurred in methane seep communities at all depths. Further geochemical, geological and microbiological studies are required to better characterize differences of methane seeps at different depths and reasons of these differences.

In the fall of 2020, a long-lasting and massive harmful algal bloom (HAB) with extensive fields of yellow sea foam was observed in relatively cold waters (7-13 degrees C) off the coasts of the Kamchatka Peninsula, Russia. According to the estimates based on bio-optical parameters in satellite imagery, the Kamchatka bloom 2020 lasted for two months and covered a vast area of more than 300 x 100 km. An abundance of dead fish and invertebrates, including sea urchins, sea anemones, chitons, cephalopods, bivalves were found on shore during the bloom. Animals suffered almost 100% mortality within a depth range between 5 and 20 m. To identify the causative microalgal species, light and scanning electron microscopy, Raman spectroscopy, and molecular phylogenetic approaches were used. The HAB area was estimated by the spectral analysis of satellite-derived imagery. The causative organisms were unarmored dinoflagellates of Karenia species. Their density and biomass reached 100-620 cells center dot mL-1 and 1300-7700 mg center dot m-3, respectively, which accounted for 31-99% of the total cell density and 82-99% of the total phytoplankton biomass in late September to mid-October. The dominant species was Karenia selliformis, and the other co-occurring kareniacean species were K. cf. cristata, K. mikimotoi, K. papil-ionacea, K. longicanalis, and two unidentified morphotypes of Karenia spp. The molecular phylogeny inferred from LSU rDNA and ITS region showed that K. selliformis from Kamchatka in 2020 belonged to the cold-water group I and was identical to K. selliformis strains from Hokkaido, Japan, identified in 2021. This is the first HAB event caused by K. selliformis recorded from Russian coastal waters.

A new species of echinoderid kinorhynch, Echinoderes beringiensis sp. nov., collected from bacterial mats at the deep-sea cold methane seepages area on the Chukchi slope (Bering Sea, NW Pacific), is described using light and scanning electron microscopy. This new representative of the most diverse kinorhynch genus is characterized by its unique arrangement of spines, tubes and glandular cell outlets and cuticular plates composition on trunk segment 11, thus being distinguished from other congeners. Modified glandular cell outlets type 2 are present in subdorsal, laterodorsal, sublateral and ventrolateral positions on trunk segment 2; in midlateral position on trunk segment 5; in sublateral position on trunk segment 8 in males, and in midlateral and sublateral position in female. Acicular spines are present in middorsal position on trunk segments 4–8, and in lateroventral position on trunk segments 6–9. Tubes are present in lateral accessory position on trunk segment 5. Trunk segment 11 has two tergal and two sternal cuticular plates. Echinoderes beringiensis sp. nov. constitutes the first kinorhynch species described from extreme, deep-sea environments of cold methane seepages in the Pacific Ocean, and the second representative of the Kinorhyncha known from the Bering Sea .

Several species of kinorhynchs, including representatives of Pycnophyes schornikovi Adrianov, 1999 in Adrianov et Malakhov, 1999 and Condyloderes shirleyi Neuhaus et Higgins, 2019 in Neuhaus et al.2019, previously known from other localities in the Pacific Ocean, were found in detritus washed off the material of bacterial mats collected at the cold methane seeping area on the Chukchi bathyal slope in the Bering Sea. These specimens were studied and illustrated using light (DIC) and electron (SEM) microscopy to analyze morphological variations within representatives of these species collected from rather distant localities in the Pacific Ocean. Redescription of P. schornikovi is provided with careful mapping of all sensory spots, setae and glandular cell outlets, not sufficiently illustrated in the original description. Current taxonomic contributions have clearly showed the taxonomic significance of these structures, becoming a standard element in taxonomic descriptions of kinorhynchs. P. schornikovi appears to be the first eurybathic species of the Pycnophyidae in the Pacific, being distributed from shallow water to bathyal depth. C. shirleyi, characterized by a marked variation of some diagnostic morphological features even in the type locality in the North-East Pacific, appears only the second representative of the genus Condyloderes with the transoceanic (amphipacific) distribution. Both these species, P. schornikovi and C. shirleyi, constitute the first representatives of these genera in the Bering Sea. In the Pacific Ocean, kinorhynchs still have never been reported from the extreme environments of cold seeps. P. schornikovi and C. shirleyi appear to be the first representative of the genus found in the methane seepage area. Deep-sea communities of this cold seepage area are described and illustrated with ROV facilities. Biogeography discussion for both species and probable explanation of the transoceanic (amphipacific) distribution of Condyloderes shirleyi are suggested and illustrated.

A new species of echinoderid kinorhynchs, Echinoderes xiphophorus sp. nov. collected from oxidized brown silt at the deepest depression in the Sea of Japan, North-West Pacific, is described and illustrated using light and electron microscopy. This new representative of the most speciose kinorhynch genus is characterized by the unique set of spines and tubes and can easily be distinguished from most of its congeners. The second trunk segment bears three pairs of tubes in subdorsal, midlateral and ventrolateral position in both sexes; one pair of tubes on trunk segment 5 in lateroventral position and on trunk segment 8 in sublateral position; aciculate lateroventral spines on trunk segments 6–9; aciculate middorsal spines on trunk segments 4, 6, 8. This species is well recognized by very long tergal extensions of the posteriormost segment, some of the longest within the family Echinoderidae. Males of Echinoderes xiphophorus sp. nov. are well distinguished from all the congeners by extremely long sword-like appendages dorsally to three pairs of penile spines. The species constitutes the first deep-sea representative of the Echinoderidae in the Sea of Japan and the deepest representative of the Kinorhyncha in this sea.

In 2018, in the Scientific and Educational Complex “Primorsky Oceanarium” of the National Scientific Center for Marine Biology (NSCMB) FEB RAS, a Collective Use Center (CUC) was created with scientific equipment, coastal and near-shore infrastructure, unique facilities and biological materials. In its function, this Center is a unit for cooperation between fishery science and academic science in marine biotechnology (MBC). It was organized using principles of shared access of participants to marine areas, coastal research stations, biological and instrumental basis of Marine Mammals Research facility in “Primorsky Oceanarium” MBC structure in the form of CUC can be used in addressing a wide range of tasks in implementing knowledge intensive marine biotechnologies, upgrading bionic methods in the study of aquatic organisms, carrying out field studies and tests on hydroacoustic, electrical, fishing gear and other manipulators for moving behavior of aquatic organisms and their adaptation to fishing activity. The first MBC joint research results are shown. Those studies include research on acoustic and kinematic activity and characteristics of signals of marine mammals and fish, hydroacoustic emitters testing for controlling fish behavior, experimental studies on reflective properties of aquatic irganisms, and influence of attracting and repelling hydroacoustic emitters on fish behavior in cages using modern instrumental control and observation tools.

During KuramBio and KuramBioIl (Kuril Kamchatka Biodiversity Studies) expeditions of 2012 and 2016 years, 12 sites across the Kuril-Kamchatka abyssal plain and 11 sites along Kuril-Kamchatka Trench area (KKT) were surveyed and sampled and benthic communities were investigated. Samples, which comprised over 300 echiurans from 12 species of 11 genera belonging to the family Bonelliidae and Thalassematidae, were collected. The family Bonelliidae is most common in abyssal and hadal environments in the world ocean with high abundances in all investigated regions, while Thalassematidae is reported first time from the hadal depth. Species identified as representative of the genera Maxmueileria have been noted first time in Pacific. Previously known echiuran Bonellia pacifica suggested to be Pseudoikedella achaeta. The description of deep-water echiurans from the investigated areas is the second one based on complete specimens with living colouration. The descriptions provide new information on the distribution, abundance, morphology and taxonomic details of the species, which were previously noted from the northwestern Pacific and described from damaged or incomplete specimens. The knowledge of the geographic ranges of these genera are expanded and discussed.

A new species of echinoderid kinorhynchs, Echinoderes vulcanicus sp. nov. collected from detritus washed off deep-water sponges collected at the slope of active marine volcano Piip in the Bering Sea, North-West Pacific, is described and illustrated using light and scanning electron microscopy. This new representative of Echinoderes, the most specious kinorhynch genus, is characterized by a unique set of characters and is easily distinguished from the other congeners. This species is well recognized by the structure of the terminal segment having large, broadly rounded sternal plates prominently extending beyond shorter tergal extensions. Both sternal and tergal plates of this segment have prominent terminal fringe with long and thick tips. The second trunk segment bears a pair of adhesive tubes; trunk segment 5 with pair of tubes in lateroventral position; acicular lateroventral spines on trunk segments 6-9; acicular middorsal spines on trunk segments 4-8; trunk segment 10 with pair of tubules in lateroventral position; males possess three pairs of penile spines. E. vulcanicus sp. nov. constitutes the first kinorhynch species found at the top of the active marine volcano and the first representative of the Kinorhyncha in the Bering Sea. (c) 2020 Elsevier GmbH. All rights reserved.

В 82-м рейсе НИС «Академик М. А. Лаврентьев» проведены комплексные исследования экосистем, ассоциированных с гидротермальными выходами и холодными высачиваниями Берингова моря. Получены новые данные о составе и структуре донных сообществ вулкана Пийпа. На Корякском склоне Берингова моря открыт новый район холодных высачиваний. На сегодняшний день восстановительные сообщества Корякского склона являются наиболее северными сообществами такого рода из известных в Пацифике и самыми северными в мире, где встречены ныне живущие двустворчатые моллюски плиокардиины.

On cruise 82 voyage of the R/V Akademik M.A. Lavrentyev, comprehensive studies of ecosystems associated with hydrothermal vents and cold seeps in the Bering Sea were carried out. New data on the composition and structure of benthic communities of the Piip volcano were obtained. A new area of cold seeps has been discovered on the Chukchi slope of the Bering Sea. At present, the chemosynthesis communities of the Chukchi slope are the northernmost of their kind known in Pacific, and the Chukotka population of Calyptogena is the northernmost Recent population of pliocardiines in the World Ocean.

A new species of echinoderid kinorhynchs, Echinoderes ultraabyssalis sp. nov. collected from oxidized brown clay at the deepest depression of the Kuril-Kamchatka Trench, North-West Pacific, is described and illustrated using light and electron microscopy. This new representative of the largest kinorhynch genus is characterized by the unique set of spines and tubules and can be easily distinguished from other congeners. The first trunk segment shows remarkably wrinkled posterior margin with parallel cuticular notches; the second trunk segment bears pair of adhesive tubules in both sexes; trunk segment 5 with pair of tubules in lateroventral position; trunk segment 8 with lateral accessory tubules; trunk segment 9 with tubules in laterodorsal position; acicular lateroventral spines on trunk segments 6-9 and two acicular middorsal spines on trunk segments 6 and 8. This species is also well recognized by the presence of tooth-like middorsal protuberance on trunk segment 11. Echinoderes ultraabyssalis sp. nov. constitutes the deepest kinorhynch species described so far (9411-9541 m) and the first hadal representative of the Kinorhyncha in the World Ocean.

— The first comprehensive study of the deep-sea ecosystems of the Emperor Chain seamounts (the northwestern Pacific Ocean) was conducted in July–August 2019 by A.V. Zhirmunsky National Scientific Center of Marine Biology, FEB RAS. The expedition, using a remote-operated underwater vehicle Comanche 18 , was aimed at the study of distribution of typical underwater landscapes and key taxa of Octocorallia corals and Hexactinellida sponges in the vulnerable marine ecosystem of the seamounts. New data on the macrobenthos biodiversity and biogeographic characteristics of deep-sea corals and sponges, which are the dominant animals in the studied area, are presented. The survey has shown changes of the coral fauna in the latitudinal direction and obtained new data on the biogeographic boundary in the area of the Emperor Chain seamounts.

During the 82nd cruise of RV Akademik M. A. Lavrentyev a multidisciplinary study of the ecosystems associated with hydrothermal vents and cold seeps in the Bering Sea was conducted. New data on the composition and structure of benthic communities of the Piip's Volcano are obtained. On the Koryak slope of the Bering Sea, a new cold seep region was discovered. Chemosynthesis-based communities on the Koryak slope are the northern-most of their kind in the Pacific, and the Koryak population of Calyptogena is the northern-most Recent population of pliocardiines in the World Ocean.