Hadal Depths Research Articles

A Large Aggregation of Liparids at 7703 meters and a Reappraisal of the Abundance and Diversity of Hadal Fish

Few biological studies have investigated the hadal depths within oceanic trenches that plummet from 6000 meters (m) to the full ocean depth of almost 11,000 m. Here we present the deepest known in situ observations of fish: a hadal snailfish, Pseudoliparis amblystomopsis (Andriashev 1955), from 7703-m deep in the Japan Trench, which was obtained using a baited video lander. The maximum number of fish we observed was unexpectedly higher than trawl catch records of any known hadal fish. We describe changes in fish abundance and associated behaviors over time, including feeding, resting, and swimming. In light of these new observations, we reappraise the occurrence and diversity records of hadal fishes that have been constructed from fragmentary and often misleading information derived from historical explorations and global data sets. This reappraisal suggests that hadal fish diversity may be lower—although some hadal fish species may attain much larger populations—than previously thought.

Traces of dissolved particles, including coccoliths, in the tests of agglutinated foraminifera from the Challenger Deep (10,897 m water depth, western equatorial Pacific)

We examined four multilocular agglutinated foraminiferan tests from the Challenger Deep, the deepest point in the world's oceans and well below the depth at which biogenic and most detrital minerals disappear from the sediment. The specimens represent undescribed species. Three are trochamminaceans in which imprints and other traces of dissolved agglutinated particles are visible in the orange or yellowish organic test lining. In Trochamminacean sp. A, a delicate meshwork of organic cement forms ridges between the grain impressions. The remnants of test particles include organic structures identifiable as moulds of coccoliths produced by the genus Helicosphaera. Their random alignment suggests that they were agglutinated individually rather than as fragments of a coccosphere. Trochamminacean sp. C incorporates discoidal structures with a central hole; these probably represent the proximal sides of isolated distal shields of another coccolith species, possibly Hayaster perplexus. Imprints of planktonic foraminiferan test fragments are also present in both these trochamminaceans. In Trochamminacean sp. B, the test surface is densely pitted with deep, often angular imprints ranging from roughly equidimensional to rod-shaped. The surfaces are either smooth, or have prominent longitudinal striations, probably made by cleavage traces. We presume these imprints represent mineral grains of various types that subsequently dissolved. X-ray microanalyses reveal strong peaks for Ca associated with grain impressions and coccolith remains in Trochamminacean sp. C. Minor peaks for this element are associated with coccolith remains and planktonic foraminiferan imprints in Trochamminacean sp. A. These Ca peaks possibly originate from traces of calcite remaining on the test surfaces. Agglutinated particles, presumably clay minerals, survive only in the fourth specimen (‘ Textularia’ sp.). Here, the final 4–5 chambers comprise a pavement of small, irregularly shaped grains with flat surfaces and no obvious intervening cement. Our observations suggest that (1) small biogenic particles can reach the deepest parts of the ocean intact in rapidly sinking phytodetrital aggregates or faecal pellets and (2) some agglutinated foraminifera living at extreme hadal depths construct a test from biogenic or detrital particles, which subsequently dissolve, leaving imprints and other remnants in the organic matrix of the test.

Discovery of Dense Aggregations of Stalked Crinoids in Izu-Ogasawara Trench, Japan

Stalked crinoids are recognized as living fossils that typically inhabit modern deep-water environments exceeding 100 m. Previous records of stalked crinoids from hadal depths (exceeding 6000 m) are extremely rare, and no in-situ information has been available. We show here that stalked crinoids live densely on rocky substrates at depths over 9000 m in the Izu-Ogasawara Trench off the eastern coast of Japan, evidenced by underwater photos and videos taken by a remotely operated vehicle. This is the deepest in-situ observation of stalked crinoids and demonstrates that crinoid meadows can exist at hadal depths close to the deepest ocean floor, in a fashion quite similar to populations observed in shallower depths.

A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca)

A summary of literature records of Polyplacophora and Monoplacophora from below 2000 m is presented. Reports have been published of 11 described species of monoplacophorans and twice as many polyplacophorans from abyssal and hadal depths. Additionally taken into account are several records of deep water species of uncertain taxonomic position in both classes. Occurrence and geographic distribution are briefly discussed.

Foreword*

Humanity has always been fascinated by organisms which survive in the most extreme and hostile environments and one such environment, is the hadal depths of the ocean trenches. Life can exist here in a food deprived habitat at enormous pressure and as far from the sun as possible, and yet it thrives. Which kinds of organisms can are found there and where did they come from? Is it a refuge for old phylogenetic lines elsewhere gone extinct or is it a habitat for highly specialized species? Considering that the trenches constitute only a minor part of the deep sea, the trenches have received the lion’s share of scientific attention. The first ‘Trench’ exploration consisted of depth soundings made during the Challenger expedition in 1872-1876, but biological deep sea sampling started in earnest with the Danish Galathea expedition II 1950-1952 which managed to make collections at the deepest parts of the trenches. Even today the trenches hold many mysteries although the focus has changed somewhat from biology to biochemistry, especially carbon sequestration (Shirayama 1997; Takeuchi et al. 1999; Nakamura & Inagaki 2005).

Tanaidacea (Crustacea: Peracarida) from Japan III. The deep trenches; the Kurile-Kamchatka Trench and Japan Trench

Examination of the tanaidacean fauna of the Kurile-Kamchatka Trench and the Japan Trench, from the surrounding edges of the trench to the hadal depths, revealed 21 new species, belonging to the genera Agathotanais, Akanthophoreus, Carpoapseudes, Cryptocopoides, Fageapseudes, Larsenotanais, Leptognathia, Leptognathiella, Neotanais, Paragathotanais, Pseudotanais, and Siphonolabrum, and 15 of these new species are described in this volume. Five additional species (Forcipatia rotundicauda, Leptognathiopsis langi, Paranarthrura vitjazi, Paranarthrura zevinae, Torquella angularis, and Typhlotanais compactus) are re-described/re-combined. The tanaidacean species richness in the trenches was found to be remarkably higher than in shallow water, although numbers of individuals were rather small; this was compensated for by high taxonomic diversity.

Four Protobranch Bivalves Collected by the ROV Kaiko from Hadal Depths in the Japan Trench

Four Protobranch Bivalves Collected by the ROV Kaiko from Hadal Depths in the Japan Trench

Biochemical composition and trophic strategies of the amphipod Eurythenes gryllus at hadal depths (Atacama Trench, South Pacific)

Amphipods Eurythenes gryllus were collected at 7800 m depth in the Atacama Trench (South Pacific) for studying their biochemical composition (in terms of proteins, lipids and carbohydrates and fatty acid content) and to gather information on bioenergetic strategies and trophic habits of organisms living in this extreme environment. The effect of long-term formalin storage on the biochemical determinations was also determined. Proteins were the dominant biochemical class of organic compounds (39–53%D.W.), whereas carbohydrates accounted for a very small fraction (1–2%D.W.). Lipid concentrations of E. gryllus accounted for 7–18%D.W. and were much lower than those reported for other deep-sea amphipods. These differences are likely to be more dependent upon food availability in the Atacama Trench rather than upon temperature. Lipid composition of E. gryllus revealed the dominance of monounsaturated fatty acids with polyunsaturated fatty acids accounting for a very small fraction, suggesting that hadal amphipods are higher dependent upon lipid reserves than amphipods inhabiting at shallow depths. The ratio of C18:1Δ9 to C18:1Δ11 was >11 confirming the necrophagous trophic habits of this hadal amphipod.

A depocenter of organic matter at 7800 m depth in the SE Pacific Ocean

The Atacama trench, the deepest ecosystem of the southern Pacific Ocean (ca. 8000 m depth) was investigated during the Atacama Trench International Expedition. Sediments, collected at three bathyal stations (1040–1355 m depth) and at a hadal site (7800 m) were analyzed for organic matter quantity and biochemical composition (in terms of phytopigments, proteins, carbohydrates and lipids), bacterial abundance, biomass and carbon production and extracellular enzymatic activities. Functional chlorophyll- a (18.0±0.10 mg m −2), phytodetritus (322.2 mg m −2) and labile organic carbon (16.9±4.3 g C m −2) deposited on surface sediments at hadal depth (7800 m) reached concentrations similar to those encountered in highly productive shallow coastal areas. High values of bacterial C production and aminopeptidase activity were also measured (at in situ temperature and 1 atm). The chemical analyses of the Atacama hadal sediments indicate that this trench behaves as a deep oceanic trap for organic material. We hypothesize that, despite the extreme physical conditions, benthic microbial processes might be accelerated as a result of the organic enrichment.

Biodiversity of nematode assemblages from deep-sea sediments of the Atacama Slope and Trench (South Pacific Ocean)

Nematode assemblages were investigated (in terms of size spectra, sex ratio, Shannon diversity, trophic structure and diversity, rarefaction statistics, maturity index, taxonomic diversity and taxonomic distinctness) at bathyal and hadal depths (from 1050 to 7800 m) in the deepest trench of the South Pacific Ocean: the Trench of Atacama. This area, characterised by very high concentrations of nutritionally-rich organic matter also at 7800-m depth, displayed characteristics typical of eutrophic systems and revealed high nematode densities (>6000 ind. 10 cm −2). Nematode assemblages from the Atacama Trench displayed a different composition than at bathyal depths. At bathyal depths 95 genera and 119 species were found (Comesomatidae, Cyatholaimidae, Microlaimidae, Desmodoridae and Xyalidae being dominant), whereas in the Atacama Trench only 29 genera and 37 species were encountered (dominated by Monhysteridae, Chromadoridae, Microlaimidae, Oxystominidae and Xyalidae). The genus Monhystera (24.4%) strongly dominated at hadal depths and Neochromadora, and Trileptium were observed only in the Atacama Trench, but not at bathyal depths. A reduction of the mean nematode size (by ca. 67%) was observed between bathyal and hadal depths. Since food availability was not a limiting factor in the Atacama Trench sediments, other causes are likely to be responsible for the reduction of nematode species richness and body size. The presence of a restricted number of families and genera in the Atacama Trench might indicate that hadal sediments limited nematode colonisation. Most of the genera reaching very high densities in Trench sediments (e.g., Monhystera) are opportunistic and were responsible for the significant decrease of the maturity index. The dominance of opportunists, which are known to be characterised by small sizes, might have contributed to the reduced nematode size at hadal depths. Shannon diversity and species richness decreased in hadal water depth and this pattern was more evident at genus than at species level. Epistrate feeders dominated and increased their relevance, determining a reduction of the index of trophic diversity at hadal depths. According to trophic diversity, taxonomic diversity and distinctness also decreased with depth. All diversity indices from the Atacama Slope and Trench were lower than in other equally deep areas world wide (e.g. Puerto Rico Trench). We suggest that such reduction was related to the high nutrient loading observed in this system (up to two orders of magnitude higher than in typical oligotrophic deep-sea sediments).

Soft-shelled benthic foraminifera from a hadal site (7800 m water depth) in the Atacama Trench (SE Pacific): preliminary observations

Abstract. Soft-shelled foraminifera (organic-walled allogromiids and agglutinated saccamminids) are an important component of the deep-sea meiofauna. Although these largely monothalamous taxa are common at bathyal and abyssal sites in almost all oceans, there are only two records from hadal depths. Here we report the occurrence of numerous allogromiids and saccamminids in a sample collected at 7800 m water depth in the Atacama Trench. The >20 μm fraction of the core sample (0–6 cm layer) yielded a total of 546 soft-walled specimens, the vast majority of them Rose Bengal stained, belonging to 20 morphospecies. Most specimens were allogromiids (82.0%), followed by saccamminids (11.0%) and psammosphaerids (6.0%). Allogromiids, particularly Nodellum- and Resigella-like forms, were responsible for a distinct peak around 120–160 μm in the size distribution, while the spherical Allogromiid sp. 1 dominated the larger-size classes. This sample provides further evidence for the widespread occurrence of soft-walled monothalamous foraminifera in marine habitats. A form resembling Resigella is common in the Atacama Trench sample but has not been observed at abyssal sites in the Pacific Ocean or Atlantic Ocean.

Meiofauna hotspot in the Atacama Trench, eastern South Pacific Ocean

Meiofaunal assemblages were investigated (in terms of abundance, biomass, individual size and community structure) at bathyal and hadal depths (from 1050 to 7800 m) in the Atacama Trench in the upwelling sector of the eastern South Pacific Ocean, in relation to the distribution and availability of potential food sources (phytopigments, biochemical compounds and bacterial biomass) in this highly productive region. Meiofaunal density and biomass in the Atacama Trench were one to two orders of magnitude higher than values reported in other “oligotrophic” hadal systems. The Atacama Trench presented very high concentrations of nutritionally rich organic matter at 7800-m depth and displayed characteristics typical of eutrophic systems. Surprisingly, despite a decrease in chlorophyll- a and organic matter concentrations of about 50% from bathyal to hadal depths, meiofaunal abundance in hadal sediments was 10-fold higher than at bathyal depths. As indicated by the higher protein to carbohydrate ratio observed in trench sediments, the extraordinarily high meiofaunal density reported in the Atacama Trench was more dependent upon organic matter quality than on its quantity. The trophic richness of the system was reflected by a shift of the size structure of the benthic organisms. In contrast with typical trends of deep-sea systems, the ratio of bacterial to meiofaunal biomass decreased with increasing depth and, in the Atacama Trench, meiofaunal biomass largely dominated total benthic biomass. Nematodes at 7800-m depth accounted for more than 80% of total density and about 50% of total meiofaunal biomass. In hadal sediments a clear meiofaunal dwarfism was observed: the individual body size of nematodes and other taxa was reduced by 30–40% compared to individuals collected at bathyal depths. The peculiarity of this trophic-rich system allows rejection of previous hypotheses, which explained deep-sea dwarfism by the extremely oligotrophic conditions typical of deep-sea regions.

Prochaetodermatidae of the Indian Ocean collected during Soviet VITYAZ cruises 19591964 (Mollusca : Aplacophora)

Four new aplacophoran mollusc species of Prochaetodermatidae (Prochaetoderma arabicum n. sp., Chevroderma lusae n. sp., Chev. javanicum n. sp., and Chev. vityazi n. sp.) and three new records (Chev. turnerae Scheltema, Chev. paradoxum Ivanov & Scheltema, Claviderma laticarinatum Ivanov & Scheltema) are added here to those described earlier for the western Indian Ocean and Arabian Sea and Atlantic Ocean. One of the species, the abyssal Chev. turnerae, is cosmopolitan throughout the Atlantic Ocean and is here reported from the eastern and western Indian Ocean. Prochaetoderma arabicum n. sp. is the only species in the genus Prochaetoderma that has been collected in the Indian Ocean/Arabian Sea. Two eastern Indian Ocean species, both with a curiously long narrow posterium, are superficially similar; one, Chev. javanicum, occurs at hadal depths in the Java Trench and the other, Chev. vityazi, was collected from the lower continental slope. So far, no prochaetodermatid species has been collected from the Indian Ocean at depths less than 1000 m.

PROCHAETODERMATIDAE OF THE EASTERN ATLANTIC OCEAN AND MEDITERRANEAN SEA (MOLLUSCA: APLACOPHORA)

The Prochaetodermatidae is a family of spiculose vermiform aplacophoran molluscs primarily of the deep-sea benthic fauna. They are ecologically important both in numbers and dominance as well as by their omnivory. In an ongoing effort, the authors are describing this significant deep-sea group from collections that have been made worldwide from conttinental shelves to hadal depths of >5,000 m. Here the eastern Atlantic and Mediterranean species are described, a matter of 14 species, half of them new. The genus Prochaetoderma is here redefined and restricted with a redescription of the type species and designation of a neotype. Whereas prochaetodermatid species were first all considered as belonging to Prochaetoderma, differences in spicule morphology fall into 5 discrete genera. Herein are given precise diagnoses and a a key to the following genera, accompanied by the species described here: Prochaetoderma Thiele, 1902: P. raduliferum (Kowalevsky, 1901), ? P. atlanticum new species, P. boucheti new species, P. yongei Schteltema, 1985; Chevroderma Scheltema, 1985: Ch. turnerae, Ch. gauson, Ch. scalpellum, all Scheltema, 1985: Claviderma new name: Cl. brevicaudatum new species, Cl. gladiatum (Salvini-Plawen, 1992), Cl. tricosum new species; Niteomica Ivanov, 1996b: N. hystrix new species; and Spathoderma Scheltema, 1985: S. clenchi Schelterma, 1985, S. alleni new species, S. grossum new species. In total, 3,568 specimens have been examined from depths between 50 and >5,000 m from the West European Basin, including the Bay of Biscay, the Mediterranean Sea, and the Iberian, Cape Verde, Guinea, Angola, and Cape Basins.

Biodiversity and historical biogeography of stalked crinoids (Echinodermata) in the deep sea

About 95 species of stalked crinoids are now described from 60m to hadal depths, but our knowledge remains far from complete. Depending on which species concept is used, estimates of species richness can be dramatically different. It is necessary to have a homogeneous concept for taxonomic units. The abundance of the crinoid fossil record allows a discussion of the ancestry of deep sea crinoid fauna. Stalked crinoids have a horizontal diversity pattern with three regional centres of high diversity (i.e. western tropical Pacific, western tropical Atlantic and north-eastern Atlantic). Vertical patterns show two faunal strata which vary in importance among provinces. The epibathyal stratum has apparently remained relatively similar in intertropical areas since the Mesozoic. Despite environmental changes related to glaciation since the Middle Miocene, the deepest crinoid fauna (i.e. the deep sea fauna sensu stricto at depths more than 1000 ± 200 m) have a very ancient origin with a dispersion closely related to plate tectonics. The bathyal fauna on hard substrates includes a few living fossils and has a high historical interest.

Nematode assemblages of deep-sea and shelf break sites in the North Atlantic and Mediterranean Sea

The nematode community structure of several shelf break and deep-sea stations in the North Atlantic and the Mediterranean is compared using data from the literature. Samples from 2 Mediterranean deep-sea canyons have a unique fauna of predatory and scavenging nematodes (e.g. Synonchiella, Halichoanolaimus, Gammanema) which comprise some 20 to 30% of the community, while some of the typical deep-sea genera (Theristus, Acantholaimus) are only marginally present. The nematode generic composition of the other sites reveals a gentle transition from the shelf break (Bay of Biscay; Mediterranean) over the slope (Mediterranean) towards the continental rise, abyssal plain and hadal depths (Bay of Biscay, Puerto Rico Trench, HEBBLE site, Hatteras Abyssal Plain). At all these sites predators and omnivores are less abundant (

Benthic associations in bathyal and hadal depths off the Pacific coast of north eastern Japan: physiognomies and site factors

Off north-eastern Japan, the continental slope is rather narrow. It slopes steeply down to a depth of 1000m, but then forms a flat terrace between 1000 and 3000 m. Beyond 3000m the slope drops steeply down to the axis of the Japan Trench (7500m). Only one community type occurs in the upper bathyal zone (200–600m), an Ophiura association whose physiognomy is a “turf” of ophiuroids. The middle bathyal zone (600–1200m) is occupied by two types of community. The predominant community is an association characterized by an asteroid, Ceramaster, and a demersal fish, Sebastolobus, which has no characteristic physiognomy. The second is a comatulid community, which occurs on the shoulder of the slope as a comatulid “park”. The lower bathyal zones (1200–3000m) is inhabited by two distinct associations one of which has two facies. Most of the terrace area is occupied by an amphiurid association. In the plateau-like areas where there is a higher flow regime, there are sporadic, or sometimes rather dense stands of a coelenterate — the Radicipes facies. Whereas at the deeper site current are slower and the sediment is muddy, a Megayoldia — Ascorhynchus facies occurs in which a bivalve and a gigantic pycnogonid are found associated with amphiurids. The other community-type is a tubicolous-polychaete association which consists of a dominant polychaete species with a rather thin sandy tube which is associated always with a caprellid. This association is found on a shoulder-like topography, where bottom currents are expected to be constant and sediment is sandy. In the axis of the Japan Trench, where the sediment is soft mud, a small globular bivalve, Kelliella, is numerically dominant, which is associated with a holothurian, Elpidia, and a demersal fish, Careproctus. Nearby where the topography is a gentle slope, the community is typified by a dominant isopod, Storthyngura sp., accompanied by a bivalve, Spinula, and an actiniarian, Galatheanthemum.

Isolation of an Obligately Barophilic Bacterium and Description of a New Genus, Colwellia gen. nov.

Summary An obligately barophilic bacterium, designated strain BNL-1, was isolated in the laboratory, under deepsea conditions of 2 °C and 740 atm hydrostatic pressure, from a sample of particle-rich seawater collected at a hadal depth of 7,410 m in the Puerto Rico Trench of the Atlantic Ocean. Its minimum, optimum, and maximum growth pressures at 2°C were 1,020 atm hydrostatic pressure, respectively. At 10°C., all cardinal growth pressures shifted upwards about 200 atm, but at no tested pressure was the organism capable of growth at 15°C. Most rapid generation time, 7 h, was observed at 10°C and 925 atm. Selected taxonomic tests and a G+C % mol ratio of 45.7 indicate the strain belongs to the vibrioenteric group of bacteria. However, evolutionary tree and principal coordinates analyses, based on the ribonucleotide sequences of 5S ribosomal RNA from BNL-1 and other bacteria, indicate its distinction at the generic level from all but one member of this group, including other known barophiles. We recommend that a new genus, Colwellia gen. nov., be established and that the obligate barophile, strain BNL-1, be designated Colwellia hadaliensis , gen. nov. sp. nov. We further recommend the renaming of Vibrio psychroerythrus ATCC 27364, the organism with which BNL-1 shares most recent common ancestry, as Colwellia psychroerythrus comb. nov.

Scavenging amphipods from the floor of the Philippine trench

Abstract Free vehicle, baited camera, and baited trap stations at 9600 and 9800 m on the bottom of the axis of the Philippine Trench demonstrate the presence of only one mobile scavenger, the amphipod Hirondellea gigas. This amphipod congregates in large numbers, consumes the bait in a matter of hours, and then disperses. Similar concentrations of amphipods have been recorded for all bait studies at hadal depths to date. In none of these did fish appear, even though they are characteristic of all samplings at shallower depths. The reason for this is obscure. Specimens of H. gigas can be classified according to developmental stage and sex. Except for stages ♂1 and ♀2, the stages are equivalent to instars, of which there are seven to eight for females and four for males. Brooding females were not trapped. The growth ratio is relatively constant among instars, except in the female where it decreases markedly during the period when there is a strong increase in the accumulation of reproductive products. Evidence favors the view that females breed only once. If this is so, total fecundity averages about 97 oocytes per female. Many H. gigas individuals had material in their guts that was ingested before being trapped. The fraction of such individuals decreased linearly with increasing maturity. A major fraction of the volume of this ingested material often consisted of bacteria. Several hypotheses are consistent with this result.

Horizons in plant pathology-II the romance of rhizosphere: A new blossoming

The present endeavor is an attempt to portray rhizosphere as viewed through the prism of plant pathology. The unifying denominator of the tangled dynamics of rhizosphere is the rich leakage from the proliferating plant roots — the exudate. The rhizosphere has been successively portrayed as (1) affording tenancy to micro-organisms, (2) as a marauder's nest and (3) as the Nature's culture laboratory of the hadal depths — this being a booming concept on the canvas of plant pathology. The author's excursion shows several well mapped terrains and unexplored frontiers awaiting explorations by the intrepid adventures into the veiled dynamics of rhizosphere.