Bathyal Depths Research Articles

‘Hitchhiker’ polynoid polychaetes in cold deep waters and their potential influence on benthic soft bottom food webs

AbstractWe describe a new association for Antarctica, involving an holothuroid host,Bathyplotes bongrainiVaney, 1914, and a parasitic polynoid polychaete,Eunoe opalinaMcIntosh, 1885, which lives on the host body. Both species have never been recorded in the study area, the Ross Sea. The ecological definition of this partnership is difficult to assess, being a mix of phoresis, protective association, parasitism and, possibly, kleptocommensalism.Eunoe opalinaemerges also as a true predator, ingesting several food items that do not belong to the diet ofBathyplotes. We compare this association with analogous examples known from shallow tropical environments as well as bathyal and abyssal depths. Given the conspicuous similarities between the deep water and high latitude examples of this kind of association, a possible common origin is hypothesized. Although the role of such a kind of parasitic relationships in Antarctic communities remains to be fully evaluated, it seems evident that, at high latitudes, where trophic levels are simplified and food webs do not have much redundancy, the impact of such a ‘multitasking’ predator-parasite asE. opalinamight be of a greater magnitude than its shallow water tropical counterpart.

Temporal variations in the feeding habits and trophic levels of three deep-sea demersal fishes from the western Mediterranean Sea, based on stomach contents and stable isotope analyses

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 402:213-232 (2010) - DOI: https://doi.org/10.3354/meps08421 Temporal variations in the feeding habits and trophic levels of three deep-sea demersal fishes from the western Mediterranean Sea, based on stomach contents and stable isotope analyses E. Fanelli*, J. E. Cartes CSIC Institut de Ciénciès del Mar, Passeig Maritim de la Barceloneta 37-49, 08003 Barcelona, Spain *Email: efanelli@icm.csic.es ABSTRACT: Temporal variations in feeding habits and trophic levels of 3 deep-sea fishes: Hoplostethus mediterraneus, Hymenocephalus italicus and Nezumia aequalis, were investigated off the Archipelago of Cabrera (Algerian Basin). These species are representative of the 3 main trophic guilds found at bathyal depths: plankton feeders, suprabenthos feeders and epi-endobenthos feeders. Samples were collected during 6 trawl surveys at bi-monthly intervals from August 2003 to June 2004, between 550 and 750 m depths. Stomach content and stable isotope analyses were performed to detect temporal variations in diet. Because fish were immediately fixed in 10% formalin, a parallel experiment comparing isotope composition in fixed and freshly frozen tissues was carried out. H. mediterraneus mainly preyed on isopods throughout the sampling period and to a lesser extent on amphipods and mysids, although mixing models revealed high consumption of mesopelagic fish in winter and spring. H. italicus fed on mysids and amphipods that live in the benthic boundary layer, while N. aequalis exhibited a more benthic diet composed of benthopelagic and benthic prey (e.g. tanaids and polychaetes). Temporal variation was observed in the diet of H. mediterraneus, with February being the period of change in feeding habits. Temporal changes were also evident, though weaker than in H. mediterraneus, in the diets of the 2 macrourids, H. italicus and N. aequalis. Patterns of temporal change in fish diets follow temporal variations in prey, which are stronger in mesopelagic than in suprabenthic or benthic fauna. Temporal variations in tissue δ15N were detected in the 3 species, with the lowest values occurring in September and the highest in April to June. In general, different time lags were detected between the isotopic turnover time of consumers and that of their diets (prey) at a monthly time scale, showing that assimilation times depend on species behaviour and metabolism. Assimilation times are brief in H. mediterraneus but last up to 2 mo in the benthic feeder N. aequalis. The experiment comparing fixed versus frozen tissues showed that formalin did not affect δ15N values after 6, 12 and 24 mo of preservation, while δ13C signatures were depleted to different extents in the 3 species compared with controls. KEY WORDS: Hoplostethus mediterraneus · Hymenocephalus italicus · Nezumia aequalis · Stomach contents · Stable isotopes · Mixing models · Temporal variations · Formalin preservation Full text in pdf format Supplementary material PreviousNextCite this article as: Fanelli E, Cartes JE (2010) Temporal variations in the feeding habits and trophic levels of three deep-sea demersal fishes from the western Mediterranean Sea, based on stomach contents and stable isotope analyses. Mar Ecol Prog Ser 402:213-232. https://doi.org/10.3354/meps08421Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 402. Online publication date: March 08, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Habitat heterogeneity and its influence on benthic biodiversity in oxygen minimum zones

AbstractOxygen minimum zones (OMZs; midwater regions with O2 concentrations <0.5 ml l−1) are mid‐water features that intercept continental margins at bathyal depths (100–1000 m). They are particularly well developed in the Eastern Pacific Ocean, the Arabian Sea and the Bay of Bengal. Based on analyses of data from these regions, we consider (i) how benthic habitat heterogeneity is manifested within OMZs, (ii) which aspects of this heterogeneity exert the greatest influence on alpha and beta diversity within particular OMZs and (iii) how heterogeneity associated with OMZs influences regional (gamma) diversity on continental margins. Sources of sea‐floor habitat heterogeneity within OMZs include bottom‐water oxygen and sulphide gradients, substratum characteristics, bacterial mats, and variations in the organic matter content of the sediment and pH. On some margins, hard grounds, formed of phosphorites, carbonates or biotic substrata, represent distinct subhabitats colonized by encrusting faunas. Most of the heterogeneity associated with OMZs, however, is created by strong sea‐floor oxygen gradients, reinforced by changes in sediment characteristics and organic matter content. For the Pakistan margin, combining these parameters revealed clear environmental and faunal differences between the OMZ core and the upper and lower boundary regions. In all Pacific and Arabian Sea OMZs examined, oxygen appears to be the master driver of alpha and beta diversity in all benthic faunal groups for which data exist, as well as macrofaunal assemblage composition, particularly in the OMZ core. However, other factors, notably organic matter quantity and quality and sediment characteristics, come into play as oxygen concentrations begin to rise. The influence of OMZs on meiofaunal, macrofaunal and megafaunal regional (gamma) diversity is difficult to assess. Hypoxia is associated with a reduction in species richness in all benthic faunal groups, but there is also evidence for endemism in OMZ settings. We conclude that, on balance, OMZs probably enhance regional diversity, particularly in taxa such as Foraminifera, which are more tolerant of hypoxia than others. Over evolutionary timescales, they may promote speciation by creating strong gradients in selective pressures and barriers to gene flow.

The roles of habitat heterogeneity in generating and maintaining biodiversity on continental margins: an introduction

(introduction to Special Issue: The roles of habitat heterogeneity in generating and maintaining biodiversity on continental margins A Contribution to the Census of Marine Life)

Cenozoic record of elongate, cylindrical, deep-sea benthic foraminifera in the North Atlantic and equatorial Pacific Oceans

In the late Pliocene–middle Pleistocene a group of 95 species of elongate, cylindrical, deep-sea (lower bathyal–abyssal) benthic foraminifera became extinct. This Extinction Group (Ext. Gp), belonging to three families (all the Stilostomellidae and Pleurostomellidae, some of the Nodosariidae), was a major component (20–70%) of deep-sea foraminiferal assemblages in the middle Cenozoic and subsequently declined in abundance and species richness before finally disappearing almost completely during the mid-Pleistocene Climatic Transition (MPT). So what caused these declines and extinction? In this study 127 Ext. Gp species are identified from eight Cenozoic bathyal and abyssal sequences in the North Atlantic and equatorial Pacific Oceans. Most species are long-ranging with 80% originating in the Eocene or earlier. The greatest abundance and diversity of the Ext. Gp was in the warm oceanic conditions of the middle Eocene–early Oligocene. The group was subjected to significant changes in the composition of the faunal dominants and slightly enhanced species turnover during and soon after the rapid Eocene–Oligocene cooling event. Declines in the relative abundance and flux of the Ext. Gp, together with enhanced species loss, occurred during middle–late Miocene cooling, particularly at abyssal sites. The overall number of Ext. Gp species present began declining earlier at mid abyssal depths (in middle Miocene) than at upper abyssal (in late Pliocene–early Pleistocene) and then lower bathyal depths (in MPT). By far the most significant Ext. Gp declines in abundance and species loss occurred during the more severe glacial stages of the late Pliocene–middle Pleistocene. Clearly, the decline and extinction of this group of deep-sea foraminifera was related to the function of their specialized apertures and the stepwise cooling of global climate and deep water. We infer that the apertural modifications may be related to the method of food collection or processing, and that the extinctions may have resulted from the decline or loss of their specific phytoplankton or prokaryote food source, that was more directly impacted than the foraminifera by the cooling temperatures.

Remarks on Echinodermata from the South Central Mediterranean Sea based upon collections made during the MARCOS cruise (10 to 20th April, 2007)

The MARCOS cruise, which took place in the South Central Mediterranean Sea on board the RV ‘Urania’, resulted in the collection of 27 species of Echinodermata from shallow to bathyal depths, many from around Malta (the Fisheries Management Zone). The fauna is represented by common to rare taxa already reported from the Mediterranean with the exception of the amphi-Atlantic ophiuroid Ophiotreta valenciennesi rufescens (Koehler, 1896), recorded from the Mediterranean Basin for the first time. Odontaster mediterraneus (von Marenzeller, 1893) and Luidia sarsi Lutken, 1858 are also first records for the Maltese Islands.

Molecular systematics of the marine gastropod families Trochidae and Calliostomatidae (Mollusca: Superfamily Trochoidea)

This study is the most extensive molecular study of the gastropod families Trochidae and Calliostomatidae published to date, in terms of both numbers of taxa and of gene sequences. As a result of Bayesian phylogenetic analyses of molecular sequence data from one nuclear gene and three mitochondrial genes, we propose dramatic changes to Trochidae family systematics, present the first molecular phylogeny for Calliostomatidae and include the first published sequence data for the enigmatic subfamily Thysanodontinae. Our phylogeny demonstrates that within the family Trochidae there is strong support for three subfamilies new to traditional classifications: Alcyninae subfam. nov., Fossarininae and Chrysostomatinae subfam. nov. As proposed, Alcyninae consists only of the nominotypical genus Alcyna, which is sister to all other trochids. The subfamily Fossarininae, as defined here, includes Fossarina, Broderipia, Synaptocochlea and "Roya"eximia and probably also Clydonochilus and Minopa. The subfamily Chrysostomatinae comprises the genera Chrysostoma and Chlorodiloma. Additional molecular support is also obtained for recently redefined Trochinae, Monodontinae, and Cantharidinae and for the traditionally recognised subfamilies Umboniinae and Stomatellinae. The subfamily Lirulariinae is not supported by the molecular data, but rather is incorporated into Umboniinae. We also demonstrate that the current concept of the subfamily Margaritinae (previously a trochid subfamily, but recently and provisionally assigned to Turbinidae) is not monophyletic. We provide preliminary evidence that whereas Margarella rosea (previously a member of Margaritinae) belongs in the trochid subfamily Cantharidinae, its presumptive congener M. antarctica is not a trochid, but instead clusters with the thysanodontine genus Carinastele. Based on the phylogenetic placement of C. kristelleae, we agree with previous proposals based on morphological data that Thysanodontinae are more closely related to Calliostomatidae than Trochidae. Both Calliostoma and Carinastele are carnivorous and if a sister relationship can be confirmed between Carinastele and Margarella antarctica it might mean that carnivory evolved twice in Trochoidea. The direction of dietary changes was not investigated in this study, but mapping diet onto the phylogeny suggests that true herbivory is predominantly a derived character. The new classification system also means that five trochid subfamilies are predominantly associated with hard substrata, one with soft substrata (Umboniinae) and two with algae and seagrass (Alcyninae and Cantharidinae). There has been a shift back to hard substrata in one umboniine clade. Two of three clades within Calliostomatidae were predominantly associated with hard substrata, but one Japanese clade is associated with sand. The finding of three new, unidentified species from very deep water means that Trochidae, like Calliostomatidae, now includes species found at bathyal depths. More deep-water species may be found as increased sampling leads to the discovery of new species.

Three new species of deep-sea Gromia (Protista, Rhizaria) from the bathyal and abyssal Weddell Sea, Antarctica

We describe three new species of the genus Gromia from bathyal and abyssal depths in the Weddell Sea. The new species are characterized by a combination of morphological and molecular criteria. All three species possess a distinct oral capsule and a layer of `honeycomb membranes', which form the inner part of the organic test wall. Both these features are typical of gromiids. Their identification as gromiids is confirmed by analyses of partial small subunit ribosomal DNA (SSU rDNA) gene sequences. Gromia marmorea sp. nov. is a rounded species with a prominent oral capsule and a characteristically mottled appearance. In Gromia melinus sp. nov., the test surface exhibits a polygonal pattern of ridges, with a layer of clay particles coating the surface between the ridges. Gromia winnetoui sp. nov. represents an elongate morphotype in which the organic test is enclosed within an agglutinated case, a feature previously unknown in gromiids. Phylogenetic analysis using the maximum-likelihood method revealed that all three species form distinct clades, reflecting the morphological differences among Weddell Sea species, as well as between deep-water Southern Ocean Gromia and previously described gromiids.

Morphological, ecological and molecular characterization of the enigmatic planispiral snail genus Adeuomphalus (Vetigastropoda: Seguenzioidea)

Adeuomphalus Seguenza, 1876 is a little known genus among the skeneimorph vetigastropods, with very few specimens previously reported alive from the deep sea. We examined newly collected and museum-stored specimens from upper to lower bathyal depths in the Atlantic, Mediterranean, Pacific and Indian Oceans and recognize seven recent species in the genus: A. ammoniformis Seguenza, 1876, A. densicostatus (Jeffreys, 1884), A. trochanter Waren & Bouchet, 2001, A. sinuosus (Sykes, 1925) n. comb., A. guillei n. sp., A. elegans n. sp. and A. collinsi n. sp., along with a fossil species, A. bandeli (Schroder, 1995) from the Lower Cretaceous, Poland. These species are characterized by a minute and colourless shell with almost perfectly planispiral whorls, an orthocline aperture, distinct radial ribs and a deeply concave apex and base. At least three species are confirmed to be radula-less, while A. guillei n. sp. has a simplified (3 -2-1-2-3) rhipidoglossate radula. Anatomical investigations of A. collinsi n. sp. and A. trochanter revealed the following traits: a monopectinate ctenidium, blunt and tapering cephalic tentacles with sensory papillae, a cylindrical snout, a simple right neck lobe, a large foot with the anterior corners drawn out into finger-like projections, a smooth ESO-tentacle and a single, micropapillate epipodial tentacle on each side of the foot; absence of pigmented eyes, eye lobes, cephalic lappets and subocular peduncles. Three species collected by submersibles in the vicinity of hydrothermal vents co-occurred with carnivorous sponges of the family Cladorhizidae; a parasitic mode of life is suggested based on the lack of the radula and the peculiar, tube-like shape of the snout. Separate and combined phylogenetic analyses of mitochondrial (COI and 16S rRNA) and nuclear (histone H3 and 18S rRNA) gene sequences revealed six monophyletic groups in Seguenzioidea: Seguenziidae, Chilodontidae, Calliotropidae, Cataegidae, Spinicalliotropis and skenei- morph seguenzioids. Three included skeneimorphs (A. elegans n. sp., Xyloskenea sp. and Ventsia tricari- nata) were ambiguously grouped together with long branches and low statistical supports, possibly suggesting a vast, undiscovered phylogenetic diversity of the group. Taxonomic composition, mor- phological characteristics and evolutionary history are discussed for the skeneimorphs and five other groups in the superfamily.

The Recent Coralliophilinae of the New Zealand region, with descriptions of two new species (Gastropoda: Neogastropoda: Muricidae)

The twenty Recent species of the muricid subfamily Coralliophilinae known from the New Zealand region are recorded and illustrated. The following eight species are reported for the first time from New Zealand: Babelomurex nakamigawai (Kuroda, 1959), Coralliophila sp. aff. sertata, C. solutistoma Kuroda Shikama in Shikama, 1966, Hirtomurex marshalli Oliverio, 2008, Latiaxis pilsbryi Hirase, 1908, Leptoconchus sp., Mipus matsumotoi Kosuge, 1985 and Rhizochilus sp. cf. antipathum Steenstrup, 1850. The species previously recorded as Neothais clathrata (A. Adams, 1854) from New Zealand is actually Coralliophila squamosissima (E.A. Smith, 1876). Two new species are described from bathyal depths: Hirtomurex tangaroa n. sp., and Hirtomurex taranui n. sp. Four species (Coralliophila sertata (Hedley, 1903), C. sp. aff. sertata, Hirtomurex tangaroa n. sp. and H. taranui n. sp.) are restricted to the South-West Pacific, with the latter three possibly endemic to the New Zealand region. All the New Zealand species have planktotrophic development, and 60% of them live in deep water.

Cryptic species in Gemmuloborsonia (Gastropoda: Conoidea)

During a broad molecular taxonomic and phylogenetic survey of the gastropod superfamily Conoidea, 80 specimens of several species of the genus Gemmuloborsonia were sequenced for the cytochrome c oxidase subunit I gene. The genus, originally established for fossil species from the Plio-Pleistocene of the Philippines, now includes living species from bathyal depths of the Indo-Pacific Oceans. The molecular data demonstrated the presence of five separate entities, while only four ‘morphospecies’ could be isolated by visual examination. The two largest groups, representing separate species from the molecular data, were impossible to distinguish with certainty using shell or anatomical characters. To examine shell morphology in more detail the shape of the last whorl was analysed by Fourier analysis, and the Fourier coordinates were used in canonical variate analysis. The majority of the specimens were separated into two groups, but 21.6% of the specimens were impossible to distinguish by morphological characters. One of these two forms was attributed to the known species Gemmuloborsonia moosaiSysoev & Bouchet, 1996, while the other is described as a new species Gemmuloborsonia clandestina. Bathytoma colorataSysoev & Bouchet, 2001 is transferred to Gemmuloborsonia on the basis of molecular analysis and radular morphology. Another species, represented in our material by a single specimen, remains undescribed.

High densities and depth-associated changes of epibenthic megafauna along the Aleutian margin from 2000–4200 m

The Aleutian margin is a dynamic environment underlying a productive coastal ocean and subject to frequent tectonic disturbance. In July 2004, we used over 500 individual bottom images from towed camera transects to investigate patterns of epibenthic megafaunal density and community composition on the contiguous Aleutian margin (53°N 163°W) at depths of 2000 m, 3200 m and 4200 m. We also examined the influence of vertical isolation on the megafaunal assemblage across a topographic rise at 3200 m, located 30 km from the main margin and elevated 800 m above the surrounding seafloor. In comparison to previous reports from bathyal and abyssal depths, megafaunal densities along the Aleutian margin were remarkably high, averaging 5.38±0.43 (mean±1 standard error), 0.32±0.02 to 0.43±0.03 and 0.27±0.01 individuals m−2 at 2000 m, 3200 m and 4200 m, respectively. Diversity at 2000 m was elevated by 15–30% over the deeper sites (3200–4200 m) depending on the metric, while evenness was depressed by ~10%. Levels of richness and evenness were similar among the three deeper sites. Echinoderms were the most abundant phylum at each depth; ophiuroids accounted for 89% of individuals in photographs at 2000 m, echinoids were dominant at 3200 m (39%), and holothurians dominated at 4200 m (47%). We observed a 26% reduction in megafaunal density across the summit of the topographic rise relative to that documented on the continental slope at the same depth. However, the two communities at 3200 m were very similar in composition. Together, these data support the modified ‘archibenthal zone of transition’ framework for slope community patterns with distinct communities along the middle and lower slope (the upper slope was not evaluated here). This study fills a geographical gap by providing baseline information for a relatively pristine, high-latitude, deep-sea benthic ecosystem. As pressures grow for drilling, fishing and mining on high-latitude margins, such data can serve as a reference point for much-needed studies on the ecology, long-term dynamics, and anthropogenically induced change of these habitats.

A natural history of the deep-sea aplacophoran Prochaetoderma yongei and its relationship to confamilials (Mollusca, Prochaetodermatidae)

Previously published studies are woven together into a natural history of a deep-sea aplacophoran mollusc species, Prochaetoderma yongei Scheltema, 1985, and its confamilial species in the Prochaetodermatidae. This amphi-Atlantic species occurs sometimes in great numbers at upper bathyal depths, rivaling polychaetes in numerical dominance. It appears to be an opportunist, with wide geographic and depth distribution, rapid development from lecithotrophic larva to settlement and maturity, and omnivory. A short illustrated morphological description using characters useful for identifying all prochaetodermatid species should prove useful to nontaxonomists whose business is the deep-sea benthic fauna.

Bathymetric patterns of deep‐sea gastropod species diversity in 10 basins of the Atlantic Ocean and Norwegian Sea

AbstractBathymetric patterns of macrofaunal species diversity are best documented in the western North Atlantic where diversity is a unimodal function of depth, peaking in the mid‐bathyal zone and being depressed in the upper slope and abyss. There are few inter‐basin studies of diversity‐depth trends that are controlled for taxonomy, sampling gear, and diversity measures. In this paper, we compare gastropod diversity gradients in the North American Basin of the Atlantic to estimates of diversity in 9 other regions: the Norwegian Sea, West European Basin, Guiana Basin, Gambia Basin, Equatorial Mid‐Atlantic, Brazil Basin, Angola Basin, Cape Basin and Argentine Basin. All samples were collected with epibenthic sleds, and diversity calculated by the Sanders‐Hurlbert normalized expected number of species. While sampling in other regions is generally less complete than in the western North Atlantic, results indicate that a unimodal pattern is not universal. Diversity can increase, decrease or show no relationship with depth. The level of diversity also varies among basins relative to the western North Atlantic, being depressed in the Norwegian Sea, at bathyal depths in the eastern North Atlantic, and below an oxygen minimum zone in the Cape Basin, and generally elevated at tropical latitudes and in abyssal regions where food supply is high. Associations between gastropod diversity and the ecology and geology of basins suggest that productivity, oxygen concentration, hydrographic disturbance and evolutionary‐historical processes may be implicated in shaping bathymetric diversity gradients, but specific causes are difficult to discern. Much more intensive sampling, analyses of other major taxa, and more detailed ecological data are necessary to understand deep‐sea biogeography at within‐ and between‐basin spatial scales.

Colonization patterns along the equatorial West African margin: Implications for functioning and diversity maintenance of bathyal and abyssal communities

In the framework of the deep-sea environmental programme BIOZAIRE (Ifremer-Total), colonization trays were deployed for 283–433 days at three sites along the equatorial West African margin: ZA at 1300-m depth, ZC at 4000-m depth far from the Congo canyon and ZD at 4000-m depth close to the Congo canyon. The experiments aimed at determining the influence of depth and local environmental settings on macrofaunal colonization patterns and organic carbon degradation rates. The trays were filled with glass beads and this artificial substrate was enriched with ground particulate organic matter in a gradient of 0%, 0.34%, 1.02% and 3.43% organic carbon. The highest rates of organic carbon degradation ranged, according to the duration of the experiments, from 1.59 to 2.36 gC m −2 day −1 but were independent of depth or location. Colonization rates, conversely, varied by one order of magnitude between bathyal and abyssal experiments. The influence of experimental treatments on the structure of the colonizing macrofauna also varied according to location and depth. At ZA, colonization patterns were highly predictable and driven by a shift in dominance of opportunistic taxa along the enrichment gradient. To a lesser extent, this was also true at ZD, near the Congo canyon, while at ZC the treatments had no significant effect on the composition of the colonizing fauna. At abyssal depth, high rates of organic matter degradation associated with low rates of colonization suggested that pulse of organic matter would mainly benefit the resident community. At bathyal depth, high colonization rates of a specialized fauna might conversely play an important role in the functioning of the ecosystem. The regional and local coexistence of an opportunistic fauna via a spatial storage effect associated with dispersal might significantly contribute to the maintenance of high diversity on continental margins.

The White Coral Community in the Central Mediterranean Sea Revealed by ROV Surveys

White coral communities consist of scleractinian corals that thrive in the ocean’s bathyal depths (~ 200–4000 m). In the Atlantic Ocean, white corals are known to form complex, three-dimensional structures on the seabed that attract vast amounts of other organisms, accumulate suspended detritus, and influence the local hydrodynamic flow field. These attributes coincide with what we generally describe as a coral reef. With time, environmental change causes decline of the framework-constructing corals; this is followed by erosion of the reef sequence or its draping with noncoral-related deposits. After several such sequences, the structures are known as coral carbonate mounds, which can grow as high as 350 m. Both bathyal white coral reefs and mounds are widely distributed in the Atlantic Ocean and adjacent marginal seas, such as the Gulf of Mexico. The Mediterranean Sea, however, known for its richness of fossil white coral communities exposed in land outcrops, harbors very few extant coral communities. The HERMES project extended its study sites deep into the Mediterranean with state-of-the-art mapping and visualization technology. By doing so, many previously unknown coral sites were discovered during inspections of Mediterranean narrow shelves, canyon walls, escarpments, and seamounts by remotely operated vehicles. Such shelf and continental margin settings are characteristic of the dynamic margins of the Mediterranean Sea and contrast significantly with the much broader shelves of the Atlantic Ocean. This paper reports on a HERMES cruise that was dedicated to exploring these rough submarine topographies in search of white coral communities in the central Mediterranean, and re-evaluates the general perception of the assumed paucity of white corals in this sea.

BATHYSIPHON (FORAMINIFERIDA) AT PACHECO PASS, CALIFORNIA: A GEOPETAL, PALEOCURRENT, AND PALEOBATHYMETRIC INDICATOR IN THE FRANCISCAN COMPLEX

Abstract We document a new locality for the foraminiferid Bathysiphon at Pacheco Pass, California, a classic blueschist-facies location on the eastern edge of the Franciscan Complex. The nearly featureless, silicified tubes of Bathysiphon cf. aaltoi Miller, 1986 described here are the largest reported from the Franciscan Complex; they are <153 mm long and easily recognized in the field. The rarity of fossils in the Franciscan Subduction Complex has hindered field mapping and, thus, a better understanding of its stratigraphy and structure. Bathysiphon specimens can be used as geopetal indicators, since they occur parallel to bedding at the top of argillaceous layers, as paleocurrent indicators (showing a SSE trend at Pacheco Pass), and as paleobathymetric indicators, suggesting, by their large size, mid-to-lower bathyal depths (2000–4000 m).

Perturbation at the sea floor during the Paleocene–Eocene Thermal Maximum: Evidence from benthic foraminifera at Contessa Road, Italy

Detailed analyses of the benthic foraminiferal assemblages extracted with the cold acetolyse method together with high resolution geochemical and mineralogical investigations across the Paleocene/Eocene (P/E) boundary of the classical succession at Contessa Road (western Tethys), allowed to recognize and document the Paleocene–Eocene Thermal Maximum (PETM) interval, the position of the Benthic Extinction Event (BEE) and the early recovery of benthic faunas in the aftermath of benthic foraminiferal extinction. The stratigraphical interval spanning the P/E boundary consists of dominantly pelagic limestones and two prominent marly beds. Benthic foraminifera indicate that these sediments were deposited at lower bathyal depth, not deeper than 1000–1500 m. The Carbon Isotope Excursion (CIE) interval is characterized by high barite abundance with a peak at the base of the same stratigraphic interval, indicating a complete, although condensed record of the early CIE. A succession of events and changes in the taxonomic structure of benthic foraminifera has been recognized that may be of use for supra-regional stratigraphic correlation across the P/E boundary interval. The composition of the benthic foraminiferal assemblages, dominated by infaunal taxa, indicates mesotrophic and changing conditions on the sea floor during the last ∼ 45 kyr of the Paleocene. The BEE occurs at the base of the CIE within the lower marly bed and it is recorded by the extinction of several deep-water cosmopolitan taxa. Then, the lysocline/CCD rose and severe carbonate dissolution occurred. Preservation deteriorated, the faunal density and simple diversity dropped to minimum values and a peak of Glomospira spp. has been observed. Stress-tolerant and opportunistic groups, represented mainly by bi-and triserial taxa, dominate the low-diversity post-extinction assemblages, indicating a benthic foraminiferal recovery under environmental unstable conditions, probably within a context of sustained food transfer to the bottom. A three-phase pattern of faunal recovery is recognizable. At first the lysocline/CCD started to descend and then recovered. Small-sized “ Bulimina”, Oridorsalis umbonatus, and Tappanina selmensis rapidly repopulated the severely stressed environment. Later on, Siphogenerinoides brevispinosa massively returns, dominating the assemblage together with other buliminids, Nuttallides truempyi, and Anomalinoides sp.1. Finally, a marked drop in abundance of S. brevispinosa is followed by a bloom of the opportunistic and recolonizer agglutinated Pseudobolivina that, for the first time, is recorded within the main CIE. A second interval of dissolution, but less severe than the previous one, has been recognized within the upper marly bed (uppermost part of the main CIE interval) and it is interpreted as a renewed, less pronounced shoaling of the lysocline/CCD that interrupted the recovery of benthic faunas. This further rise likely represents a response to persistent instability of ocean geochemistry in this sector of the Tethys before the end of the CIE. In the CIE recovery and post CIE intervals, the composition of the benthic foraminiferal assemblages suggests mesotrophic and unstable conditions at the sea floor. According to the geochemical proxy for redox conditions, the deposition of the PETM sediments at Contessa Road occurred in well-oxygenated waters, leading out a widespread oxygen depletion as major cause of the BEE. Changing oceanic productivity, carbonate corrosivity and global warming appear to have played a much more important role in the major benthic foraminiferal extinction at the P/E boundary.

Cenozoic sedimentary rocks on the northern slopes of the Kuril Deep-Water Basin (Sea of Okhotsk) and conditions of their formation

Sedimentary rocks from the northern slope of the Kuril Deep-Water Basin are examined. Four different-age lithological units are distinguished, and inferences about the probable conditions of their formation are made. The Paleogene-Lower Miocene deposits (lithological units I and II) are represented by the purest varieties of siliceous rocks, which implies their accumulation far away from the source areas under quiet hydrodynamical conditions of the waters. The composition of the microfossils suggests a relatively shallow-water marine basin. The Pliocene-Pleistocene deposits of lithological units III and IV were formed in an active hydrodynamical environment under conditions of synchronous explosive volcanism at bathyal depths. The presence of porcelanite outcrops on the continental slope of the basin, together with the micropaleontological data about the paleodepths of the sedimentation, allows us to assume that, in the region studied, the continental slope was formed as a result of vertical motions in the post-Middle Miocene time.

Faunal responses to oxygen gradients on the Pakistan margin: A comparison of foraminiferans, macrofauna and megafauna

The Pakistan Margin is characterised by a strong mid-water oxygen minimum zone (OMZ) that intercepts the seabed at bathyal depths (150–1300 m). We investigated whether faunal abundance and diversity trends were similar among protists (foraminiferans and gromiids), metazoan macrofauna and megafauna along a transect (140–1850 m water depth) across the OMZ during the 2003 intermonsoon (March–May) and late/post-monsoon (August–October) seasons. All groups exhibited some drop in abundance in the OMZ core (250–500 m water depth; O2: 0.10–0.13 mL L?1=4.46–5.80 ?M) but to differing degrees. Densities of foraminiferans >63 ?m were slightly depressed at 300 m, peaked at 738 m, and were much lower at deeper stations. Foraminiferans >300 ?m were the overwhelmingly dominant macrofaunal organisms in the OMZ core. Macrofaunal metazoans reached maximum densities at 140 m depth, with additional peaks at 850, 940 and 1850 m where foraminiferans were less abundant. The polychaete Linopherus sp. was responsible for a macrofaunal biomass peak at 950 m. Apart from large swimming animals (fish and natant decapods), metazoan megafauna were absent between 300 and 900 m (O2 0.2 mL L?1=8.92 ?M). The progressively deeper abundance peaks for foraminiferans (>63 ?m), Linopherus sp. and ophiuroids probably represent lower OMZ boundary edge effects and suggest a link between body size and tolerance of hypoxia. Macro- and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa, indicating that the lower part of the OMZ is also a region of rapid faunal change. Species diversity was depressed in all groups in the OMZ core, but this was much more pronounced for macrofauna and megafauna than for foraminiferans. Oxygen levels strongly influenced the taxonomic composition of all faunal groups. Calcareous foraminiferans dominated the seasonally and permanently hypoxic sites (136–300 m); agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were >0.13 mL L?1(=5.80 ?M). Polychaetes were the main macrofaunal taxon within the OMZ; calcareous macrofauna and megafauna (molluscs and echinoderms) were rare or absent where oxygen levels were lowest. The rarity of larger animals between 300 and 700 m on the Pakistan Margin, compared with the abundant macrofauna in the OMZ core off Oman, is the most notable contrast between the two sides of the Arabian Sea. This difference probably reflects the slightly higher oxygen levels and better food quality on the western side.