Bathyal Depths Research Articles

A critical review of Antarctic Conoidea (Neogastropoda)

ABSTRACTThe Antarctic Conoidean fauna is critically reviewed based on published data and specimens in the collections of the USNM, IORAS and MNHN. Forty-two species and subspecies of the superfamily Conoidea are recorded as occurring within the Antarctic Convergence (excluding the fauna of the Kerguelen Islands) and are attributed to 14 genera and seven families. These include the new taxa: Antarctospira n. gen. (type species—Leucosyrinx badenpowelli Dell, 1990); Drilliola antarctica n. sp.; Pleurotomella (Pleutoromella) tippetti n. sp.; Pleurotomella (Anomalotomella) petiti n. sp.; Xanthodaphne pastorinoi n. sp. Aforia watsoni is introduced as a new name for Pleurotoma (Surcula) lepta Watson, 1881, non Pleurotoma lepta Edwards, 1861. A lectotype is designated for Conorbella antarctica (Strebel, 1908). New combinations are also proposed. Antarctospira badenpowelli (Dell, 1990), n. comb. (previously assigned to Leucosyrinx); Antarctospira principalis (Thiele, 1912), n. comb. (previously assigned to Typhlomangelia); Antarctospira mawsoni (Powell, 1958), n. comb. (previously assigned to Leucosyrinx); Typhlodaphne paratenoceras (Powell, 1951), n. comb. (previously assigned to Leucosyrinx); Belalora weirichi (Engl, 2008), n. comb. (previously assigned to Oenopota); Pleurotomella (Anomalotomella) innocentia (Dell, 1990), n. comb. (previously assigned to Typhlodaphne); Pleurotomella (Anomalotomella) nipri (Numanami, 1996), n. comb. (previously assigned to Typhlodaphne); Xanthodaphne raineri (Engl, 2008), n. comb. (previously assigned to Pleurotomella); Aforia hedleyi (Dell, 1990), n. comb. (previously assigned to Pontiothauma). The majority of Antarctic conoidean taxa have hypodermic marginal teeth. Although there is a similar relative abundance of conoideans in Antarctic waters to that seen in other well-studied faunas, the low number of conoideans is indicative of the general impoverishment of the gastropod fauna in the region. Fourteen percent (2 of 14) of conoidean genera that occur within the Antarctic Convergence are endemic to Antarctic waters, as are 82% (34 of 42) of the species. Most taxa have very broad bathymetric ranges, some extending from bathyal to hadal depths. The greatest species diversity was at bathyal depths.

USING MULTI-FORAMINIFERAL-PROXIES TO RESOLVE THE PALEOGEOGRAPHIC HISTORY OF A LOWER MIOCENE, SUBDUCTION-RELATED, SEDIMENTARY BASIN (WAITEMATA BASIN, NEW ZEALAND)

A combination of five techniques was used to infer the paleobathymetry and paleoecology of 103 foraminiferal faunas (>63μm, census counts of 384 benthic species) from throughout the lower Miocene Waitemata Basin, Auckland, northern New Zealand. A canonical correspondence analysis ordination showed that environmental factors related to paleo-bathymetry were the main drivers of benthic foraminiferal composition and samples were sorted in approximate paleo-depth order using increasing planktic percentage and species diversity proxies. Cluster analysis recognised seven associations (A–G) and eight subassociations, which were interpreted in terms of paleo-bathymetry and paleoproductivity by qualitative comparison with modern faunas. Planktic-percentage-based regression (with benthic stress-indicator taxa removed) and a Modern Analogue Technique comparison (at generic level) of fossil benthic assemblages with a modern dataset (626 faunas from 0–5000 m) were both used to provide quantitative paleo-bathymetry estimates for each Miocene fauna. These paleo-depth estimates were refined using the upper- and lower-depth limits of some of the less common benthics present. No one technique appears to be better than others. All can provide anomalous paleo-bathymetric estimates that need to be explained. Paleo-depth estimates are most consistent and precise for inner–mid shelf faunas and become less precise and more frequently inconsistent with increasing depth. A number of faunas with inconsistent paleo-bathymetric estimates contain both shallow- and deep-water-restricted benthic tests. These are interpreted as resulting from the inclusion of reworked deep-water fossil tests into shallow faunas, or mixing of contemporaneous tests as sediment flowing from shelf depths down into the basin in turbidity currents and debris flows. The eight bathyal–abyssal associations and subassociations have overlapping depth ranges but only 3–4 of them were present in the basin at any one time. Their geographic distribution reflects a crude depth-related zonation, whereas their stratigraphic succession is inferred to have resulted from a period of increased carbon flux and decreased bottom oxygen sandwiched between periods of lower carbon flux and more oxic bottom conditions. The recognised associations are: A, Elphidium , intertidal–subtidal beach; B, Nonionella-Notorotalia , sheltered inner shelf; C, Amphistegina-Cibicides , exposed inner–outer shelf; D, Astrononion-Gyroidina , ≥mid-bathyal; E, Bolivina , mid–lower bathyal; F, Cibicides-Bolivina , bathyal; G, Oridorsalis-Neugeborina-Pullenia , ≥lower bathyal. The inferred paleoenvironment of the faunas is used to help resolve the paleogeographic history of the Waitemata Basin. Thin basal transgressive sequences of lensing conglomerate, shelly sandstone and limestone containing shelf faunas (Assocs A–C) record initiation of basin subsidence over a wide area (300 × 100 km), ~21 Ma. Continued subsidence (estimated from foraminiferal data at ~1 mm/yr) was accompanied by sediment starvation with little or no sediment accumulating until the basin reached lower bathyal depths (F, G). This created sufficient slope for turbidity currents from the north to flow down submarine canyons and deposit three interfingering submarine fans of sandstone (800–1000 m thick). Displaced Cretaceous–Oligocene nappes and melange (Northland Allochthon) moved part way into the basin from the north and large sub-seafloor slides of mixed basinal sediment and allochthon slid off its advancing toe. These slides were triggered by uplift of the northern part of the basin, which created land fringed by a wide shelf (C). A large submarine stratovolcano built up on the west side of the basin and shed volcaniclastic sediment (C, D, F) down its eastern slopes with some debris flows transporting mixed shallow water faunas up to 30 km into the basin. The ~4 million-year-life of this subduction-related basin came to an end with complete eversion before the end of the early Miocene.

Impact of ocean acidification on reproductive output in the deep-sea annelid Ophryotrocha sp. (Polychaeta: Dorvilleidae)

As increasing anthropogenic CO2 emissions are absorbed by the oceans, a decrease in seawater pH is expected to occur, causing what is now termed ocean acidification (OA). Deep-sea species have been greatly understudied with respect to OA, even though their response may differ from those evidenced so far in shallow-water taxa. The polychaete worm Ophryotrocha sp. collected at bathyal depth was held and reproduced for several years, offering a rare opportunity to study environmental effects in a member of a deep-sea community. This hermaphroditic species exhibits well defined seasonality in feeding and reproduction and its development and growth have been characterized. The purpose of the present study was to explore the effects of OA on gametogenesis following exposure to a 0.4 unit pH decrease under realistic conditions over 26 weeks. Opportunistic assessments of spawning and development were also conducted. A flow-through design allowing for natural fluctuations in pH, temperature and salinity was used. Individuals exposed to low pH/high ρCO2 produced larger and more abundant oocytes but fewer spermatozoa, compared to individuals in ambient conditions. However, lower effective fecundity (number of eggs laid) was ultimately recorded under low pH conditions, together with slower development of the embryos and larvae. Microstructure of the body wall, and appearance and elemental composition of chaeta were not affected. Despite its ability to live and reproduce normally for years in the laboratory, a realistic decrease of pH in the environment of Ophryotrocha sp. led to reproductive disruption, highlighting its potential vulnerability to OA.

Taxonomic clarification and re-description of two deep-sea roughies of genus Hoplostethus from the Indian Ocean

Two deep-sea roughies, Hoplostethus (Leiogaster) rubellopterus Kotlyar, 1980 and H. (L.) melanopus (Weber, 1913), are re-described based on several specimens collected from the Arabian Sea, Bay of Bengal and Andaman Sea. Some notes on the taxonomic status of these two species are also included, and their distributional ranges are updated. Hoplostethus (L.) rubellopterus is a commonly occurring species in the deep-sea catches from the upper continental slope (160–800 m) of this region, which is often misidentified and reported as H. mediterraneus Cuvier, 1829. Previous reports of H. mediterraneus from Indian waters were found to be misidentifications, and should be referred to H. (L.) rubellopterus. Hoplostethus (L.) melanopus is found to be distributed in much deeper waters at bathyal depths (>900 m) of the Arabian Sea and Andaman Sea.

Occurrence of a rare gigantic sized deep-sea cod Lepidion inosimae (Günther, 1887) in the Northwestern Indian Ocean

A gigantic sized (total length 800 mm) specimen of Lepidion inosimae (Gunther, 1887) was collected in a bottom trawl operated at bathyal depth (1330–1360 m) off the Southwest coast of India. The present study discloses the first distribution record of this very rarely reported deep-sea cod from the Northwestern Indian Ocean, with its morphometric and meristic features.

Late Cenomanian environmental conditions at the submerged Tatric Ridge, Central Western Carpathians during the period preceding Oceanic Anoxic Event 2 – A palaeontological and isotopic approach

Micropalaeontological and isotopic studies of the upper Cenomanian turbiditic/hemipelagic sediments from the High-Tatric unit (Central Western Carpathians; Polish part of the Tatra Mountains) has been undertaken to characterize the sedimentary conditions in the Tatric basin, a part of the Western Tethys, related to the interval preceding the late Cenomanian oceanic anoxic event (OAE2). The deposition of these sediments, including organic-rich layers (TOC up to 0.7%), corresponds to the Rotalipora cushmani foraminiferal Zone. Microfacial, foraminiferal and palynological analyses show that the sea floor was located at upper bathyal depths and the water column was poorly oxygenated. The intrabasinal carbonate material indicates moderate primary productivity with rare periods of upwellings. The scarcity of marine fossils in redeposited material and features of carbonate lithoclasts suggest very low productivity in the nearshore surface water, most probably due to a low-density hyposaline cap as surface runoff from the southern margin of the basin. The carbon isotopic study documents the negative values of δ13Ccarb in the whole section as an effect of transfer of isotopically light carbon sourced from various sources. Such negative values of δ13Ccarb are characteristic of the upper Cenomanian sediments, deposited in relatively shallow water basins, characterized by input of terrestrial organic matter and/or carbonate particles known from the Western Interior sections, the Atlantic coastal plain, the northwestern African margin, the eastern margin of the Apulian Platform and shelf sediments in the NW Europe and Tethyan Himalayas. Most probably, all of these events could be related to the global sea level fluctuations that occurred ca. 95.5–94.5 Ma comparing with the Haq (2014) eustatic curve.

Community structure and diversity of scavenging amphipods from bathyal to hadal depths in three South Pacific Trenches

There are few biological datasets that span large bathymetric ranges with sufficient resolution to identify trends across the abyssal and hadal transition zone, particularly over multiple trenches. Here, scavenging Amphipoda were collected from three trenches in the South Pacific Ocean at bathyal to hadal depths. Diversity and community structure were examined from stations within the Kermadec Trench (1490–9908m) and New Hebrides Trench (2000–6948m) and additional data were included from the South Fiji Basin (4000m) and Peru-Chile Trench (4602–8074m). The hadal community structure of the Kermadec and New Hebrides trenches were distinct from the surrounding abyssal and bathyal depths and correlated to hydrostatic pressure and POC flux. Low POC flux in the New Hebrides Trench and South Fiji Basin best explained the dissimilarity in abyssal community structure from those of the disparate Kermadec and Peru-Chile trenches. POC flux also best explained patterns in hadal community structure with the Kermadec and New Hebrides Trench communities showing greater similarity to each other than to the eutrophic Peru-Chile Trench. Hydrostatic pressure was the strongest driver of intra-trench assemblage composition in all trench environments. A unimodal pattern of species diversity, peaking between 4000 and 5000m, was best explained by hydrostatic pressure and temperature.

Biology of a deep-water sea anemone (Anthozoa: Actiniidae) from eastern Canada: Spawning, development, and growth

Knowledge of the general biology and reproductive ecology of deep-water species can help predict their resilience to environmental and anthropogenic disturbances. The present study centers on live specimens of a deep-water sea anemone which were collected at bathyal depths between 1100 and 1400m and kept in a mesocosm for over 6 years. Morphology and DNA sequencing confirmed that the species belongs to the genus Urticina. Male and female (9–10cm pedal disk diameter, 90 tentacles) spawned 4 years post collection, in early spring (March). Both sexes released gametes through the mouth. The negatively buoyant oocytes (550–600µm in diameter) quickly settled on the rocks and soft sediments surrounding the female. Lecithotrophic embryonic and larval development occurred on the substratum. Fully developed planula larvae were detected after 17–21 days. Planulae started to crawl and swim around but remained demersal. Metamorphosis and settlement occurred after 30–35 days, exclusively on hard substrata and preferentially on undersurfaces. Offspring grew slowly, developing 8 tentacles after 5 months and 24 tentacles after 12 months (3–4mm pedal disk diameter). After 2.6 years of growth, the captive-born sea anemones reached 12–16mm in pedal disk diameter and possessed 48–54 tentacles.

Reviews and syntheses: the first records of deep-sea fauna – a correction and discussion

Abstract. The soundings in deep waters of Baffin Bay, together with the recovery of a basket star by John Ross in 1818, was a milestone in the history of deep-sea research. Although the alleged water depths of up to 1950 m were by far not reached, these were nevertheless the first soundings in deep bathyal (to perhaps uppermost abyssal) depths. Furthermore, the recovery of a benthic animal proved that animal life existed at great depths. Yet this was not the first published record of deep-sea fauna as it is often portrayed. This merit goes to accidental catches of the stalked crinoid Cenocrinus asterius that were recovered with fishing lines from upper bathyal environments near Antillean islands. In addition, the description of several deep-sea fishes considerably predated the John Ross episode.

Early Cenomanian “hot greenhouse” revealed by oxygen isotope record of exceptionally well‐preserved foraminifera from Tanzania

AbstractThe search into Earth's mid‐Cretaceous greenhouse conditions has recently been stimulated by the Tanzania Drilling Project (TDP) which has recovered exceptionally well‐preserved biogenic carbonates from subsurface pre‐Neogene marine sediments in the eastern margin of central Africa. Published Tanzanian oxygen isotope records measured on exquisitely preserved foraminiferal tests, dating to as old as ~93 Ma, provided evidence for a Turonian “hot greenhouse” with very high and stable water‐column temperatures. We have generated a comparable data set of exceptionally well‐preserved foraminifera from a lower Cenomanian interval of TDP Site 24 spanning 99.9–95.9 Ma (planktonic foraminiferal Thalmanninella globotruncanoides Zone; nannofossil Corollithion kennedyi to Lithraphidites eccentricus Zones), thereby extending the age coverage of the Tanzanian foraminiferal δ18O record back by ~7 million years. Throughout the interval analyzed, the new foraminiferal δ18O data are consistently around −4.3‰ for surface‐dwelling planktonic taxa and −1.9‰ for benthic Lenticulina spp., which translate to conservative paleotemperature estimates of >31°C at the surface and >17°C at the sea floor (upper bathyal depths). Considering the ~40°S Cenomanian paleolatitude of TDP Site 24, these estimates are higher than computer simulation results for accepted “normal” greenhouse conditions (those with up to 4X preindustrial pCO2 level) and suggest that the climate mode of the early Cenomanian was very similar to the Turonian hot greenhouse. Taking account of other comparable data sources from different regions, the hot greenhouse mode within the normal mid‐Cretaceous greenhouse may have begun by the latest Albian, but the precise timing of the critical transition remains uncertain.

Foraminiferal stratigraphy and palaeobathymetry of Paleocene-lowermost Oligocene deposits (Vezhany and Monastyrets nappes, Ukrainian Carpathians)

Mainly pelagic/hemipelagic deposits of the Vezhany Nappe (Paleocene-Lowermost Oligocene Metova Formation with a high content of planktonic foraminifera) and typical flysch deposits of the Monastyrets Nappe (Paleocene-Eocene Sushmanets Formation with common agglutinated foraminifera as well as the Eocene Drahovo Formation), of the southwestern inner part of the Ukrainian Carpathians have been studied. The Parvularugoglobigerina eugubina Zone (Lower Danian), Acarinina acarinata Zone (Upper Thanetian), Morozovella subbotinae Zone and Morozovella aragonensis Zone (Ypresian), Acarinina bullbrooki Zone and Acarinina rotundimarginata Zone (Lutetian), Subbotina corpulenta Zone and Subbotina vialovi Zone (Upper Priabonian – Lower Rupelian) based on planktonic foraminifera as well as the Rzehakina fissistomata sensu lato Zone (Paleocene), Glomospira charoides – Recurvoides smugarensis Zone (Ypresian), and an assemblage with Haplophragmoides parvulus (latest Mid Eocene-early Late Eocene) based on agglutinated foraminifera have been identified in these deposits. The deep-water agglutinated foraminifera of the “ Rzehakina ”, “ Rhabdammina ” and “ Paratrochamminoides ” assemblages found in the typical flysch deposits of the Sushmanets Formation indicate lower slope to abyssal environments below the CCD. The generic composition and morphological features of planktonic and benthic foraminifera recovered from marls of the Metova Formation suggest pelagic/hemipelagic conditions at bathyal depths above the foraminiferal lysocline.

First record of deep-sea gigantic pycnogonid Colossendeis colossea Wilson, 1881 from the Western Indian Ocean

The gigantic pycnogonid, Colossendeis colossea Wilson, 1881 is reported for the first time in the Western Indian Ocean. Two male specimens of this species were collected from a bottom trawl operated at bathyal depths (>1000 m) off the Southwest coast of India.

Sedimentary organic matter contents and porewater chemistry at upper bathyal depths influenced by the 2011 off the Pacific coast of Tohoku Earthquake and tsunami

Sedimentary organic matter and porewater geochemistry at upper bathyal depths off Tohoku, Japan, were investigated 1 year after the 2011 off the Pacific coast of Tohoku Earthquake. Total organic carbon (TOC) and total nitrogen (TN) concentrations, organic carbon and nitrogen isotopic compositions, dissolved oxygen (DO) concentrations, and bottom water and porewater nutrient concentrations were examined in sediment core samples collected from eight upper bathyal stations. Event deposits 1 to 7 cm thick were observed at all sampling stations, indicating that a vast area off Tohoku has been influenced by sedimentological events caused by the earthquake or subsequent tsunami. Both TOC and TN concentrations were lower in coarse-grained event deposits. Carbon and nitrogen isotopic composition, together with the C/N ratio, suggested that the event deposits, including turbidites, were composed of local sediments that had been transported relatively short distances. Nutrient fluxes across the sediment–water interface correlated with surface TOC and bottom water DO concentrations. However, event deposit thickness showed no correlation with oxygen or nutrient fluxes. The organic matter content of the event deposits was similar to that in the underlying sediments at each site, and thus no apparent effect of event deposits on nutrient fluxes was observed. Our results suggest that biogeochemical cycles in sediments of disturbed areas are affected not only by event deposit thickness, but also by the source of the event deposits.

Meiobenthos and nematode assemblages from different deep-sea habitats of the Strait of Sicily (Central Mediterranean Sea)

Much attention is currently devoted at upgrading our knowledge on biodiversity and functioning of deep water ecosystems. Information is constantly enriched by researchers, even from basins as the long-studied Mediterranean Sea. In such a perspective, we studied meiobenthic and nematode communities inhabiting muddy sediments from three different habitats at bathyal depths in the Strait of Sicily: a cold-water coral site (CS) in the Maltese Coral Province, a muddy bottom in the same area (MS), and a hydrocarbon imprinted pockmark site (PS) in the Gela Basin. The average meiofauna density at CS (1343 ind/10 cm2) and MS (1804 ind/10 cm2) is much higher than that reported in literature for similar habitats; it is also markedly more elevated than that recorded at PS (224 ind/10 cm2). Although nematodes of the three sites show different abundances, they share similar assemblage structure. Nematodes (avg. 86%) and copepods (avg. 9.3%) were the most abundant meiofaunal taxa at all sites followed by annelids, kinorhynchs and turbellarians. Nematodes were composed by 21 families and 46 genera, with Terschellingia, as most abundant genus (12.4%), followed by Microlaimus (11%), Daptonema (11%), Thalassomonhystera (10.8%), Acantholaimus (9.5%) and Sabatieria (8.7%). The genera Thalassomonhystera, Terschellingia, Microlaimus, Daptonema, Chromadorita, Sabatieria, and Anticoma display a dominance in at least one station. The taxonomic structure of meiofaunal communities of the studied sites is rather similar but differences in relative abundance are evident.

On an unusual shallow occurrence of the deep-sea brittle star Ophiomyces delata in the Duncan Passage, Andaman Islands (Northern Indian Ocean)

The deep-water brittle star Ophiomyces delata Koehler, 1904 is reported from the Duncan Passage, Andaman Islands, for the first time, at a relatively shallow depth of 56 m. A detailed description of the specimens is provided, as the genus Ophiomyces comprises nine nominal species that exhibit morphological plasticity and have considerable overlap in geographic range. The recently resurrected name for the family, Ophiomycetidae Verrill, 1899, is replaced with the senior synonym Ophiohelidae Perrier, 1893, and a key to genera is provided. This family represents a strongly conservative lineage among Ophiuroidea, having originated in the deep-sea and temporarily extended their range to shallow shelf settings around the middle Jurassic, before apparently retreating to bathyal and abyssal depths. The present discovery of Ophiomyces delata represents the first report of this lineage at shallow depths since the mid-Jurassic.

Reproductive biology of the seastar Ceramaster grenadensis from the deep north-western Mediterranean Sea

Ceramaster grenadensis is one of the most abundant bathyal seastars in the north-western Mediterranean Sea and also presents a wide geographic distribution in the Atlantic Ocean. As with other species in this genus, little information is available on the biology and reproductive strategy of C. grenadensis. In this context, we describe for the first time the reproductive cycle of this species from bathyal depths in the north-western Mediterranean Sea. Specimens (N = 141) were collected seasonally from 194 benthic trawls (141 Otter Trawls and 53 Agassiz trawls) conducted during 10 cruises from October 2008 to April 2013. Open slope and canyon systems were sampled at depths between 900 and 2250 m. The population distribution of C. grenadensis showed a depth-related structure, with the smaller adult specimens and juveniles present at greater depths. Sex ratio was 2:1 females per male, constant among seasons and depths. Histological analyses of the gonads showed an asynchronous ovarian organization, with previtellogenic and vitellogenic oocytes throughout the year. These oogenesis patterns suggest a continuous reproduction. However, the Pyloric Caeca Index (PCI) decreased in summer while the Gonad Index (GI) increased in autumn in males, suggesting a higher spawning capacity in autumn. In both sexes, an increasing GI and PCI trend was observed with increasing depth.

Tanaidacea (Crustacea: Peracarida) of the northeast Atlantic: Chauliopleona Dojiri and Sieg, 1997 and Saurotipleona n. gen. from the ‘Atlantic Margin’

Two akanthophoreid taxa, Chauliopleona and the new genus Saurotipleona, are modest contributors to tanaidacean diversity in the benthos of seas from Iceland to the British Isles along the ‘Atlantic Margin’. Three of H.J. Hansen’s ‘Ingolf’ species, originally within the genus Leptognathia, are rediagnosed, i.e. Chauliopleona amdrupii, C. armata and C. hastata. One new species, C. bamberi, from British waters is described and a new genus and species, Saurotipleona julii, is described from bathyal depths in the Irminger and Iceland basins. The latter is similar to Chauliopleona in having a sternal spur on pleonite-5 but this is of a slightly different form and is ventrally directed; it also has two superodistal spines on the propodus of pereopod-5, a distinctly plesiomorphic character in the family. A distribution map and key to the identification of these species are given.http://zoobank.org/urn:lsid:zoobank.org:pub:E7EF8C72-D1C6-438E-B9C2-A5CE637FB75A

Anobothrus amourouxisp. nov., a new species of Ampharetidae (Polychaeta) from the Capbreton Canyon (Bay of Biscay, NE Atlantic Ocean)

A new species of Ampharetidae,Anobothrus amourouxisp. nov., has been identified from bathyal depths of the Capbreton Canyon, Bay of Biscay (NE Atlantic Ocean). This new species is characterized by inner branchiae with transversal ciliated ridges, notochaetae from modified eighth thoracic unciniger with hirsute tips, uncini from thoracic unciniger with 6–7 teeth in lateral view arranged in two vertical rows in frontal view, fused segments II + III with paleae from SII and reduced notopodia without chaetae from SIII. An identification key for all hitherto described species of the genusAnobothrusis provided.

Submersible- and lander-observed community patterns in the Mariana and New Britain trenches: Influence of productivity and depth on epibenthic and scavenging communities

Deep-sea trenches remain one of the least explored ocean ecosystems due to the unique challenges of sampling at great depths. Five submersible dives conducted using the DEEPSEA CHALLENGER submersible generated video of undisturbed deep-sea communities at bathyal (994m), abyssal (3755m), and hadal (8228m) depths in the New Britain Trench, bathyal depths near the Ulithi atoll (1192m), and hadal depths in the Mariana Trench Challenger Deep (10908m). The New Britain Trench is overlain by waters with higher net primary productivity (~3-fold) than the Mariana Trench and nearby Ulithi, and receives substantially more allochthonous input from terrestrial sources, based on the presence of terrestrial debris in submersible video footage. Comparisons between trenches addressed how differences in productivity regime influence benthic and demersal deep-sea community structure. In addition, the scavenger community was studied using paired lander deployments to the New Britain (8233m) and Mariana (10918 m) trenches. Differences in allochthonous input were reflected in epibenthic community abundance, biodiversity, and lifestyle representation. More productive locations were characterized by higher faunal abundances (~2-fold) at both bathyal and hadal depths. In contrast, biodiversity trends showed a unimodal pattern with more food-rich areas exhibiting reduced bathyal diversity and elevated hadal diversity. Hadal scavenging communities exhibited similar higher abundance but also ~3-fold higher species richness in the more food-rich New Britain Trench compared to the Mariana Trench. High species- and phylum-level diversity observed in the New Britain Trench suggest that trench environments may foster higher megafaunal biodiversity than surrounding abyssal depths if food is not limiting. However, the absence of fish at our hadal sites suggests that certain groups do have physiological depth limits. Submersible video footage allowed novel in situ observation of holothurian orientation, jellyfish feeding behavior as well as lifestyle preferences for substrate, seafloor and overlying water. This study documents previously unreported species in the New Britain Trench, including an ulmariid scyphozoan (8233m) and an acrocirrid polychaete (994m), and reports the first observation of an abundant population of elpidiid holothurians in the Mariana Trench (10908m). It also provides the first megafaunal community analysis of the world׳s deepest epibenthic community in the Mariana Trench Challenger Deep, which was composed of elpidiid holothurians, amphipods, and xenophyophores.

Foraminifera on the Demerara Rise offshore Surinam: crustal subsidence or shallowing of an oxygen minimum zone?

AbstractThe lower bathyal Ocean Drilling Program Hole 1261A was sampled near an upper Quaternary oxygen minimum zone (OMZ). Glauconite, the percentage of the foraminiferal assemblage as benthic specimens and assemblage composition were used to investigate the behaviour of the OMZ. Benthic foraminifera and glauconite were comparable with the upper margin of the modern OMZ off California. The percentage abundances ofU. peregrinaandC. laevigatawere on the Demerara Rise negatively correlated, the proportional abundance ofU. peregrinaincreasing upwards through the section. This reflects variations in proximity to the upper margin of the OMZ. This might reflect either crustal subsidence or long-term shallowing of the OMZ during the earlier late Quaternary. Neither hypothesis can be accepted unequivocally. The purported subsidence can be ascribed to crustal loading by the Amazon and Orinoco deep-sea fans, but this would require that the palaeodepth to the top of the OMZ remains constant across several glacial–interglacial cycles. In contrast, it is difficult to envisage any mechanism that could have caused progressive shallowing of the OMZ across several glacial–interglacial cycles. The epifaunalPlanulina wuellerstorfiis related to more oxic waters and enhanced current action. This suggests that intervals with more abundantP. wuellerstorfiwere somewhat less dysoxic than those with few. These intervals approximate to those with more abundantC. laevigata. Superimposed on this low-frequency signal is a higher-frequency signal, indicated by a between-sample assemblage turnover index (ATIs) that might prove useful for long-range sequence stratigraphic correlation at bathyal depths.