Feeding Characteristics of Deep-Sea Acorn Worm (Hemichordata, Enteropneusta, Torquaratoridae) from the Bering Sea

Deep-sea hemichordates Torquaratoridae gen. sp. reach high abundance up to 12 spec. m^-2 at the depths of 1830-2130 m on the slope of the Volcanologists Massif in the south-western part of the Bering Sea, dominating in the benthic community at these depths. Their abundance exceeds by two orders the values recorded earlier. In order to clarify this phenomenon, we examined the gut contents of Torquaratoridae gen. sp. The detritus particles and frustules of planktonic diatoms Thalassiosira, Coscinodiscus, Actinocyclus, Chaetoceros, Neodenticula, and Grammatophora were the most common in the gut, as well as the remains of skeletons of benthic invertebrates with little admixture of mineral particles. According to obtained data, Torquaratoridae gen. sp. are mobile deposit feeders with high selectivity to fresh phytodetritus, able to compete with holothurians occupying similar trophic niche. Unusually high abundance of acorn worms is apparently related to high organic matter flux to the seafloor as a result of spring phytoplankton bloom in the surface water layer of the Bering Sea.

Fauna associated with shallow-water methane seeps in the Laptev Sea

Background

Methane seeps support unique benthic ecosystems in the deep sea existing due to chemosynthetic organic matter. In contrast, in shallow waters there is little or no effect of methane seeps on macrofauna. In the present study we focused on the recently described methane discharge area at the northern Laptev Sea shelf. The aim of this work was to describe the shallow-water methane seep macrofauna and to understand whether there are differences in macrobenthic community structure between the methane seep and background areas.

Methods

Samples of macrofauna were taken during three expeditions of RV Akademik Mstislav Keldysh in 2015, 2017 and 2018 using 0.1 m² grabs and the Sigsbee trawl. 21 grabs and two trawls in total were taken at two methane seep sites named Oden and C15, located at depths of 60–70 m. For control, three 0.1 m² grabs were taken in area without methane seepage.

Results

The abundance of macrofauna was higher at methane seep stations compared to non-seep sites. Cluster analysis revealed five station groups corresponding to control area, Oden site and C15 site (the latter represented by three groups). Taxa responsible for differences among the station groups were mostly widespread Arctic species that were more abundant in samples from methane seep sites. However, high densities of symbiotrophic siboglinids Oligobrachia sp. were found exclusively at methane seep stations. In addition, several species possibly new to science were found at several methane seep stations, including the gastropod Frigidalvania sp. and the polychaete Ophryotrocha sp. The fauna at control stations was represented only by well-known and widespread Arctic taxa. Higher habitat heterogeneity of the C15 site compared to Oden was indicated by the higher number of station groups revealed by cluster analysis and higher species richness in C15 trawl sample. The development of the described communities at the shallow-water methane seeps can be related to pronounced oligotrophic environment on the northern Siberian shelf.

Species richness and taxonomic composition of trawl macrofauna of the North Pacific and its adjacent seas

A checklist is presented of animal species obtained in 68,903 trawl tows during 459 research surveys performed by the Pacific Research Fisheries Center (TINRO-Center) over an area measuring nearly 25 million km² in the Chukchi and Bering seas, Sea of Okhotsk, Sea of Japan and North Pacific Ocean in 1977–2014 at depths of 5 to 2,200 m. The checklist comprises 949 fish species, 588 invertebrate species, and four cyclostome species (some specimens were identified only to genus or family level). For each species details are given on the type of trawl (benthic and/or pelagic) and basins where the species was found. Comprehensiveness of data, taxonomic composition of catches, dependence of species richness on the survey area, sample size, and habitat, are considered. Ratios of various taxonomic groups of trawl macrofauna in pelagic and benthic zones and in different basins are analysed. Basins are compared based on species composition.

Discovery of Trunk Coelomoducts in Hemichordata

Histological examination of a specimen of a deep-sea enteropneusts that belongs to a yet undescribed species (Torquaratoridae gen. sp.) revealed numerous trunk coelomoducts. They open into the genital wing coelom as a typical funnels; short ducts communicate with environment through pores located on the outer side of the genital wings. Total number of coelomoducts in a specimen is estimated at several thousand. Trunk coelomoducts have not been found earlier in any member of the phylum. We believe that the release of the male gonad products occurs through coelomoducts of Torquaratoridae gen. sp.

A strategy for the conservation of biodiversity on mid-ocean ridges from deep-sea mining

Mineral exploitation has spread from land to shallow coastal waters and is now planned for the offshore, deep seabed. Large seafloor areas are being approved for exploration for seafloor mineral deposits, creating an urgent need for regional environmental management plans. Networks of areas where mining and mining impacts are prohibited are key elements of these plans. We adapt marine reserve design principles to the distinctive biophysical environment of mid-ocean ridges, offer a framework for design and evaluation of these networks to support conservation of benthic ecosystems on mid-ocean ridges, and introduce projected climate-induced changes in the deep sea to the evaluation of reserve design. We enumerate a suite of metrics to measure network performance against conservation targets and network design criteria promulgated by the Convention on Biological Diversity. We apply these metrics to network scenarios on the northern and equatorial Mid-Atlantic Ridge, where contractors are exploring for seafloor massive sulfide (SMS) deposits. A latitudinally distributed network of areas performs well at (i) capturing ecologically important areas and 30 to 50% of the spreading ridge areas, (ii) replicating representative areas, (iii) maintaining along-ridge population connectivity, and (iv) protecting areas potentially less affected by climate-related changes. Critically, the network design is adaptive, allowing for refinement based on new knowledge and the location of mining sites, provided that design principles and conservation targets are maintained. This framework can be applied along the global mid-ocean ridge system as a precautionary measure to protect biodiversity and ecosystem function from impacts of SMS mining.

Kolgaosides A and B, Two New Triterpene Glycosides from the Arctic Deep Water Sea Cucumber Kolga hyalina (Elasipodida: Elpidiidae)

Two novel triterpene holostane nonsulfated pentaosides, kolgaosides A (1) and B (2), and one known, holothurinoside B (3), were isolated from the Arctic sea cucumber Kolga hyalina, the second representative of the family Elpidiidae, order Elasipodida, from which triterpene glycosides have been obtained. The structures of 1 and 2 were elucidated using 1H and 13C NMR and 2D NMR procedures (HSQC, HMBC, COSY, ROESY, TOCSY) and HRESI mass-spectrometry. Kolgaosides A (1) and B (2) demonstrate low cytotoxic activity against the cells of the ascite form of mouse Ehrlich carcinoma and moderate hemolytic activity against mouse erythrocytes, despite the presence of hydroxy groups in the side chains of the aglycones. The glycosides of K. hyalina are similar to those of the Antarctic sea cucumber Rhipidothuria racowitzai Hèrouard, 1901 (= Achlionice violaescupidata) (Elasipodida: Elpidiidae); this may have chemotaxonomic significance.

Kolgaosides A and B, two new triterpene glycosides from the Arctic deep water sea cucumber Kolga hyalina (Elasipodida: Elpidiidae)

Two novel triterpene holostane nonsulfated pentaosides, kolgaosides A (1) and B (2), and one known, holothurinoside B (3), were isolated from the Arctic sea cucumber Kolga hyalina, the second representative of the family Elpidiidae, order Elasipodida, from which triterpene glycosides have been obtained. The structures of 1 and 2 were elucidated using 1H and 13C NMR and 2D NMR procedures (HSQC, HMBC, COSY, ROESY, TOCSY) and HRESI mass-spectrometry. Kolgaosides A (1) and B (2) demonstrate low cytotoxic activity against the cells of the ascite form of mouse Ehrlich carcinoma and moderate hemolytic activity against mouse erythrocytes, despite the presence of hydroxy groups in the side chains of the aglycones. The glycosides of K. hyalina are similar to those of the Antarctic sea cucumber Rhipidothuria racowitzai Hèrouard, 1901 (=Achlionice violaescupidata) (Elasipodida: Elpidiidae); this may have chemotaxonomic significance.

An externally brooding acorn worm (Hemichordata, Enteropneusta, Torquaratoridae) from the Russian arctic

A single specimen of a previously undescribed acorn worm in the family Torquaratoridae was trawled from a bottom depth of about 350 m in the Kara Sea (Russian Arctic). The new species is the shallowest of the exclusively deep-sea torquaratorids found to date, possibly an example of high-latitude emergence. On the basis of ribosomal DNA sequences and morphology, the worm is described here as the holotype of Coleodesmium karaensis n. gen., n. sp. It is most similar in overall body shape to the previously described enteropneust genus Allapasus, but is uniquely characterized by a tubular component of the proboscis skeleton ensheathing the collar nerve cord. Additionally, within the proboscis, the sparseness of the musculature of C. karaensis clearly distinguishes it from the much more muscular members of Allapasus. The holotype is a female bearing about a dozen embryos on the surface of her pharyngeal region, each recessed within a shallow depression in the dorsal epidermis. The embryos, ranging from late gastrula to an early stage of coelom formation, are a little more than 1 mm in diameter and surrounded by a thin membrane. Each embryo comprises an external ectoderm of monociliated cells (not arranged in obvious ciliated bands) and an internal endo-mesoderm; the blastopore is closed. In the most advanced embryos, the anterior coelom is starting to constrict off from the archenteron. Coleodesmium karaensis is the first enteropneust (and indeed the first hemichordate) found brooding embryos on the surface of the mother's body.

Diversification of acorn worms (Hemichordata, Enteropneusta) revealed in the deep sea

Enteropneusts (phylum Hemichordata), although studied extensively because of their close relationship to chordates, have long been considered shallow-water, burrowing animals. The present paper more than doubles the number of enteropneust species recorded in the deep sea based on high-resolution imaging and sampling with remotely operated vehicles. We provide direct evidence that some enteropneusts are highly mobile-using changes in posture and currents to drift between feeding sites-and are prominent members of deep, epibenthic communities. In addition, we provide ecological information for each species. We also show that despite their great morphological diversity, most deep-living enteropneusts form a single clade (the rediagnosed family Torquaratoridae) on the basis of rDNA sequences and morphology of the proboscis skeleton and stomochord. The phylogenetic position of the torquaratorids indicates that the group, after evolving from near-shore ancestors, radiated extensively in the deep sea.