An eddy,a wake and a plume: controls on bathyal foraminifera around Tobago,western tropical Atlantic Ocean

Oceanic islands in the paths of currents induce the development of wakes and stationary eddies. The situation to the lee of Tobago, western tropical Atlantic Ocean, is further complicated by the occurrence of the seasonally variable, hypopycnal Orinoco plume. Here we investigate the impact of the combined plume, wake and eddy on bathyal benthic foraminifera to the NW of Tobago. Three surface sediment samples were recovered from around each of five well-sites to the NW of Tobago, three of the sites (Warap-A, Cassra-A and Cassra-CC) being at upper bathyal depths and two (Bene-1, Sancoche-1) at middle bathyal depths. Warap-A, Cassra-A, Cassra-CC and Bene-1 form a transect along the northern side of the leeward wake, while the other two sites are in the vicinity of the stationary eddy. The samples obtained around Sancoche-1 were taken north of the wake. These were supplemented by samples from four 80-cm piston cores from upper bathyal and outer neritic depths sampled at ~ 10 cm intervals. Benthic foraminifera reveal different biofacies at upper (Warap-A, Cassra-A, Cassra-CC) and middle (Bene-1, Sancoche-1) bathyal depths. The upper bathyal biofacies is dominated by Cassidulina curvata and the middle bathyal biofacies contains abundant Uvigerina hispidocostata, both of which are indicative of a high nutrient flux. The presence of Martinottiella communis and M. pallida at Warap-A indicate that pore waters are low in dissolved oxygen in the immediate lee of the island. Percentages of the fauna as serial tests indicated decreasing current velocities with increasing depth, as confirmed by the high abundance of Cibicides ex gr. aknerianus in the shallowest water core. Upper bathyal bottom-current strength was at its lowest in the immediate lee of the island. Species indicative of a perennial nutrient flux were more abundant to the NW, where the interaction of the plume and eddy appears to concentrate nutrients. The short cores, each from a different biofacies, indicate that these environmental conditions have been in place for at least the later Holocene. The most northerly, upper bathyal core presented a stable community structure with low assemblage turnover, while two cores taken farther south (upper bathyal and outer neritic) had an expansive structure with high assemblage turnover. These data raise the possibility of using benthic foraminifera to track the positions of the plume, core and eddy throughout the later Neogene.     

Infaunal hydraulics generate porewater pressure signals

Many activities by infauna, including burrowing and feeding, involve hydraulic mechanisms. We expected these activities to generate low-frequency pressure waves that would propagate through sediments and be detectable at some distance from the source. Pressure sensors in intertidal sediments recorded large-amplitude porewater pressure signals. Laboratory recordings of single individuals allowed us to identify characteristic signals of arenicolid and nereidid polychaetes and tellinid bivalves. In the bivalve Macoma nasuta, these high-amplitude signals were associated with burrowing, expulsion of pseudofeces, and siphon relocation. In the polychaetes Neanthes brandti and Abarenicola pacifica, the high-amplitude pressure signals were associated with burrowing, burrow construction, burrow ventilation, and defecation. These signals were detectable in the field at distances of at least 20 cm. Since the waveforms are species-specific as well as activity-specific, they may provide a mechanism for prey detection, for predator avoidance, for competitor detection, and perhaps even for mate detection.     

Large Spatial Scale Variability in Bathyal Macrobenthos Abundance,Biomass, α- and β-Diversity along the Mediterranean Continental Margin

The large-scale deep-sea biodiversity distribution of the benthic fauna was explored in the Mediterranean Sea, which can be seen as a miniature model of the oceans of the world. Within the framework of the BIOFUN project (“Biodiversity and Ecosystem Functioning in Contrasting Southern European Deep-sea Environments: from viruses to megafauna”), we investigated the large spatial scale variability (over >1,000 km) of the bathyal macrofauna communities that inhabit the Mediterranean basin, and their relationships with the environmental variables. The macrofauna abundance, biomass, community structure and functional diversity were analysed and the α-diversity and β-diversity were estimated across six selected slope areas at different longitudes and along three main depths. The macrobenthic standing stock and α-diversity were lower in the deep-sea sediments of the eastern Mediterranean basin, compared to the western and central basins. The macrofaunal standing stock and diversity decreased significantly from the upper bathyal to the lower bathyal slope stations. The major changes in the community composition of the higher taxa and in the trophic (functional) structure occurred at different longitudes, rather than at increasing water depth. For the β-diversity, very high dissimilarities emerged at all levels: (i) between basins; (ii) between slopes within the same basin; and (iii) between stations at different depths; this therefore demonstrates the high macrofaunal diversity of the Mediterranean basins at large spatial scales. Overall, the food sources (i.e., quantity and quality) that characterised the west, central and eastern Mediterranean basins, as well as sediment grain size, appear to influence the macrobenthic standing stock and the biodiversity along the different slope areas.     

Paleoenvironmental and paleoclimatic changes during the Late Cretaceous and Cretaceous–Paleogene (K/Pg) boundary transition in Tattofte,External Rif,northwestern Morocco: implications from dinoflagellate cysts and palynofacies

This paper presents a quantitative study of dinoflagellate cysts (dinocysts) and palynofacies of the Campanian–Danian marly succession at the village of Tattofte (western External Rif, northwestern Morocco). The paleoenvironmental and paleoclimatic interpretations, inferred from this palynologic analysis, are compared to coeval sequences of other areas in the Northern Hemisphere. Changes in the relative abundances of dinocyst taxa, which are paleoenvironmental indicators, throughout the section suggest a deposition in a marine inner to outer neritic setting. The upper Campanian dinocyst assemblage is characterized by the presence of outer neritic-oceanic and low productivity indicator taxa (e.g., Spiniferites spp., Odontochitina spp.) and cold-water taxa (e.g., Manumiella spp., Chantangiella spp., Laciniadinium spp.), whereas, the lower Maastrichtian assemblage is characterized by inner neritic, high productivity and warm-water indicator taxa (e.g., Palaeocystodinium spp., Andalusiella spp.). The upper Maastrichtian dinocyst assemblage displays a return to an outer neritic environment under a transgressive regime, but with a cooling pulse and a moderate productivity. However, the Cretaceous–Paleogene (K/Pg) boundary interval records remarkable changes in the relative abundances of dinocyst taxa, indicating an inner neritic (coastal) setting, which is the most proximal in the study section; such changes reflect instable paleoenvironmental conditions which may be related to global cooling periods, likely caused by the Deccan volcanism in India and/or the Chicxulub asteroid impact in Mexico at the K/Pg boundary. In the Danian, the dinocyst relative abundances indicate a gradual return to stable environmental conditions.A quantitative analysis of the kerogen plots (palynomorphs, phytoclasts and amorphous organic matter (AOM)) reveals five types of palynofacies, generally indicating oxic to suboxic marine environments. The upper Campanian and upper Maastrichtian (lowermost part) strata are characterized by a playnofacies (V), indicating a distal shelf, while the lower Maastrichtian and lower Danian (uppermost part) strata record a playnofacies (III), reflecting an intermediate inner-outer neritic environment. However, the K/Pg boundary transition is characterized by playnofacies types (I) and (II), indicating a proximal (coastal) environment.     

Imaging Oxygen Distribution in Marine Sediments. The Importance of Bioturbation and Sediment Heterogeneity

The influence of sediment oxygen heterogeneity, due to bioturbation, on diffusive oxygen flux was investigated. Laboratory experiments were carried out with 3 macrobenthic species presenting different bioturbation behaviour patterns: the polychaetes Nereis diversicolor and Nereis virens, both constructing ventilated galleries in the sediment column, and the gastropod Cyclope neritea, a burrowing species which does not build any structure. Oxygen two-dimensional distribution in sediments was quantified by means of the optical planar optode technique. Diffusive oxygen fluxes (mean and integrated) and a variability index were calculated on the captured oxygen images. All species increased sediment oxygen heterogeneity compared to the controls without animals. This was particularly noticeable with the polychaetes because of the construction of more or less complex burrows. Integrated diffusive oxygen flux increased with oxygen heterogeneity due to the production of interface available for solute exchanges between overlying water and sediments. This work shows that sediment heterogeneity is an important feature of the control of oxygen exchanges at the sediment-water interface.     

Mechanisms of spatial competition in marine soft-bottom communities

Two kinds of biogenic structures, roots of seagrasses and tubes of invertebrates, were found to reduce the mobility of a variety of burrowing species, including two polychaetes (Abarenicola pacifica Healy & Wells, A. claparedii Healy & Wells), two bivalves (Macoma nasuta Conrad, Clinocardium nuttalliiConrad), two crustaceans (Upogebia pugettensis (Dana), Callianassa californiensis Dana), a holothurian (Leptosynapta clarkii Heding), and an echinoid (Dendraster excentricus (Eschscholtz)). Comparisons of burrowing in similar sediments showed that: (a) all species had about a two-fold increase in mean time to burial in dense tube-mats of polychaetes and crustaceans; (b) hard-bodied taxa were particularly restricted by roots of Zostera marina L. and were often incapable of penetrating them; (c) roots and tubes together had the greatest impact, with mobility 3 to 37 times slower; and (d) burrowing ability increased when sediments were “pre-burrowed” for 1 day. Comparisons of burrowing rates in different sediments showed effects of physical origin (sediment compaction or sorting). Overall these physical effects were second to those of purely biogenic origin, sediment binding and cohesion by roots and tubes. Nonetheless, physical effects exceeded those of extremely high densities of tube-builders (3160 individuals ·0.01 m^?2). In all substrata the movement of larger individuals, and the larger of morphologically similar pairs of species (listed second above), were more restricted by roots and tubes than were smaller ones. The results suggest a general mechanism by which dense assemblages of tube-builders and seagrasses may restrict older and larger burrowing organisms. Because physical properties of the sediment and the abundance of other burrowers are also factors affecting mobility, it is not now possible to predict what situations will render this mechanism of interaction important to natural communities.     

Population differentiation decreases with depth in deep-sea bivalves

The deep sea is the largest ecosystem on Earth. Recent exploration has revealed that it supports a highly diverse and endemic benthic invertebrate fauna, yet the evolutionary processes that generate this remarkable species richness are virtually unknown. Environmental heterogeneity, topographic complexity, and morphological divergence all tend to decrease with depth, suggesting that the potential for population differentiation may decrease with depth. To test this hypothesis, we use mitochondrial DNA (16S rRNA gene) to examine patterns of population differentiation in four species of protobranch bivalves (Nuculoma similis, Deminucula atacellana, Malletia abyssorum, and Ledella ultima) distributed along a depth gradient in the western North Atlantic. We sequenced 268 individuals from formalin-fixed samples and found 45 haplotypes. The level of sequence divergence among haplotypes within species was similar, but shifted from between populations at bathyal depths to within populations at abyssal depths. Levels of population structure as measured by phiST were considerably greater in the upper bathyal species (N. similis = 0.755 and D. atacellana = 0.931; 530-3834 m) than in the lower bathyal/abyssal species (M. abyssorum = 0.071 and L. ultima = 0.045; 2864-4970 m). Pairwise genetic distances among the samples within each species also decreased with depth. Population trees (UPGMA) based on modified coancestry coefficients and nested clade analysis both indicated strong population-level divergence in the two upper bathyal species but little for the deeper species. The population genetic structure in these protobranch bivalves parallels depth-related morphological divergence observed in deep-sea gastropods. The higher level of genetic and morphological divergence, coupled with the strong biotic and abiotic heterogeneity at bathyal depths, suggests this region may be an active area of species formation. We suggest that the steep, topographically complex, and dynamic bathyal zone, which stretches as a narrow band along continental margins, plays a more important role in the evolutionary radiation of the deep-sea fauna than the much more extensive abyss.     

Sedimentation as a control of reef development: St. Croix,U.S.V.I.

Sediment-transport rates in and around Salt River submarine canyon, St. Croix, U.S.V.I., were measured over a 2-year period using bedload traps and Legrangian sediment-tracer experiments. Sodiments generatly move in a westerly direction along the north shore of St. Croix. Consequently, sediment moves into the canyon at a higher rate over the eastern margin (47,000 kg/m-year) than over the west wall (19,000 kg/m-year). As a result, extensive reef growth is limited to the west wall, and the inner portion of the eastern margin is a cobblecovered slope inhabited primarily by gorgonians and a few sediment-tolerant corals. Sedimentation exhibits similar controls on other reefs around the island. At Cane Bay, sedimentation rates are lower than at Salt River, and reef development is accordingly greater. Along the east side of Christiansted canyon and the downdrift margin at Sandy Point, extreme sedimentation has completely buried the reefs. Sediment transport was an order of magnitude higher during storms than during fair weather. Under all conditions measured, the amount of sediment exported from the canyon was considerably below that entering over the canyon walls. It is hypothesized that major hurricanes periodically flush the excess, and keep long-term sediment influx and export in balance.     

The second species of Gromia (Protista) from the deep sea: its natural history and association with the Pakistan margin oxygen minimum zone

We describe a gromiid protist Gromia pyriformis sp. nov., from bathyal depths on the Pakistan margin (NE Arabian Sea), an area characterised by a well-developed Oxygen Minimum Zone (OMZ). The new species is smaller (length usually <1 mm) than the only other described deep-sea gromiid species (Gromia sphaerica) or the well-known coastal species Gromia oviformis. Its identification as a gromiid is based on the test-wall ultrastructure. This includes (i) an outer wall (165-300 nm thick) limited by an electron-opaque layer and perforated by pore structures which typically extend through its entire thickness, and (ii) inner "honeycomb membrane" structures which form a discontinuous sheet (18-20 nm thick) lying parallel to the outer wall. An outermost glycocalyx (approximately 75 nm thick), not observed in other gromiid species, is also present and imparts a finely granular appearance to the outer test surface, as seen by Scanning Electron Microscopy (SEM). Numerous rod-shaped prokaryotes are attached to the exterior of the glycocalyx. Gromia pyriformis sp. nov. typically occurs above the sediment-water interface, attached to the large arborescent foraminiferan Pelosina sp. It is confined to a very narrow bathymetric zone (approximately 1000 m water depth) in the lower portion of the OMZ, where bottom-water oxygen concentrations are approximately 0.2 ml l(-1).     

On the absence of circular muscle elements in the body wall of Dysponetus pygmaeus (Chrysopetalidae, 'Polychaeta', Annelida)

The annelid body wall generally comprises an outer layer of circular muscle fibres and an inner layer of longitudinal muscle fibres as well as parapodial and chaetal muscles. An investigation of Dysponetuspygmaeus (Chrysopetalidae) with confocal laser scanning microscopy showed that circular muscles are entirely absent. Further studies indicate that this feature is characteristic for all Chrysopetalidae. A scrutiny of the literature showed a similar situation in many other polychaetes. This lack of circular muscle fibres may either be due to convergence or represent a plesiomorphic character. Since circular muscles are very likely important for burrowing forms but not necessary for animals which proceed by movements of their parapodial appendages or cilia, this problem is also related to the question of whether the ancestral polychaete was epi‐ or endobenthic.     

Explaining bathymetric diversity patterns in marine benthic invertebrates and demersal fishes: physiological contributions to adaptation of life at depth

Bathymetric biodiversity patterns of marine benthic invertebrates and demersal fishes have been identified in the extant fauna of the deep continental margins. Depth zonation is widespread and evident through a transition between shelf and slope fauna from the shelf break to 1000 m, and a transition between slope and abyssal fauna from 2000 to 3000 m; these transitions are characterised by high species turnover. A unimodal pattern of diversity with depth peaks between 1000 and 3000 m, despite the relatively low area represented by these depths. Zonation is thought to result from the colonisation of the deep sea by shallow‐water organisms following multiple mass extinction events throughout the Phanerozoic. The effects of low temperature and high pressure act across hierarchical levels of biological organisation and appear sufficient to limit the distributions of such shallow‐water species. Hydrostatic pressures of bathyal depths have consistently been identified experimentally as the maximum tolerated by shallow‐water and upper bathyal benthic invertebrates at in situ temperatures, and adaptation appears required for passage to deeper water in both benthic invertebrates and demersal fishes. Together, this suggests that a hyperbaric and thermal physiological bottleneck at bathyal depths contributes to bathymetric zonation. The peak of the unimodal diversity–depth pattern typically occurs at these depths even though the area represented by these depths is relatively low. Although it is recognised that, over long evolutionary time scales, shallow‐water diversity patterns are driven by speciation, little consideration has been given to the potential implications for species distribution patterns with depth. Molecular and morphological evidence indicates that cool bathyal waters are the primary site of adaptive radiation in the deep sea, and we hypothesise that bathymetric variation in speciation rates could drive the unimodal diversity–depth pattern over time. Thermal effects on metabolic‐rate‐dependent mutation and on generation times have been proposed to drive differences in speciation rates, which result in modern latitudinal biodiversity patterns over time. Clearly, this thermal mechanism alone cannot explain bathymetric patterns since temperature generally decreases with depth. We hypothesise that demonstrated physiological effects of high hydrostatic pressure and low temperature at bathyal depths, acting on shallow‐water taxa invading the deep sea, may invoke a stress–evolution mechanism by increasing mutagenic activity in germ cells, by inactivating canalisation during embryonic or larval development, by releasing hidden variation or mutagenic activity, or by activating or releasing transposable elements in larvae or adults. In this scenario, increased variation at a physiological bottleneck at bathyal depths results in elevated speciation rate. Adaptation that increases tolerance to high hydrostatic pressure and low temperature allows colonisation of abyssal depths and reduces the stress–evolution response, consequently returning speciation of deeper taxa to the background rate. Over time this mechanism could contribute to the unimodal diversity–depth pattern.     

Biodiversity and distribution of the genus Gromia (Protista, Rhizaria) in the deep Weddell Sea (Southern Ocean)

We present a survey of morphospecies of Gromia, a genus of testate protists, from bathyal and abyssal depths in the Weddell Sea and adjacent areas of the Southern Ocean. This material represents the most extensive and diverse available collection of deep-sea gromiids so far recorded. The twelve species, nine of which are undescribed, are recognized on the basis of morphological criteria, including the test size and shape, the appearance and structure of the oral capsule, and the characteristics of the test wall. Most species have a single oral capsule, which is circular in plan view with a conical nipple-like shape in lateral view. One morphospecies has three oral capsules. The appearance and structure of the wall displays great variability among Gromia species, ranging from very delicate and transparent with highly reflective highlights to relatively thick with distinct patterns of ridges covering the surface. More often, however, differences in wall structure are more subtle. Most morphospecies were distributed at bathyal depths along the continental margin, but one was sampled at ~4,800 m, representing the first record of an abyssal gromiid. Concurrent with findings from other regions of the World’s oceans, the Weddell Sea gromiids were mostly found in surficial sediments in areas of elevated organic input, suggesting that deep-sea gromiids are likely to play an important role in carbon cycling in bathyal eutrophic regions through the ingestion and degradation of fresh organic matter.     

Ammonite habitats in the Early Tithonian of Western Tethys

Cccca, F. 1992 07 15: Ammonite habitats in the Early Tithonian of Western Tethys.
Habitats of Early Tithonian ammonites of Western Tethys are inferred from analysis of faunal spectra, functional morphology. facies characteristics and palaeogeography. Phylloceratina and Lytoceratina are included in a pelagic group characterized by taxa which could reach bathyal depths. This group is very abundant and dominant in some localities. A neritic nektobenthic group, relatively abundant in the Cmbria-Marche Apennines only. is composed of taxa characterired by species bearing simple sutures (some Simoceratidae and Pseudolissoceras ). probably living at shallower depth. The habitat of Haplploceras and some Oppeliidae. is interpreted to be close to the shelf margin/continental slope. Perisphinctids. Aspidoceratidae and some other Oppeliidae are provisionally included in an 'indeterminate' group including deep and shallow taxa. Quantitative studies of assemblage composition and comparison of faunal spectra successions from different pelagic regions allow the characterization of different pelagic environments. Bathymetric hypotheses by means of ammonites are discussed. Z Ammonoidea. habitats. facies, faunal spectra. Jurassic, Tithonian. Tethys .     

Ecology of bathyal polychaete fauna at an Arctic-Atlantic boundary (Faroe-Shetland Channel, North-east Atlantic)

By reference to a series of 15 sampling stations spanning the West Shetland Slope (150-1000 m; Faroe-Shetland Channel, North-east Atlantic) we examined the potential environmental controls on the standing stock, diversity and composition of the polychaete fauna. In contrast to the majority of studied bathyal environments, the Faroe-Shetland Channel has a highly complex and dynamic hydrographic regime, particularly notable for extreme thermal variability at mid-slope depths (i.e. 7°C range at ca. 500 m). Contrary to general expectation, polychaete biomass increased (rather than decreased) with depth. Species diversity exhibited a parabolic pattern with depth, maximum diversity occurring at depths of 350-550 m, rather shallower than observed in other bathyal studies, and possibly linked with a maximum in habitat temperature range. Multivariate analyses of faunal composition suggested a separation of the sampling stations into a shallower and a deeper group, with temperature exerting a major control on polychaete species distributions. The decline in diversity below 600 m (i.e. the descending limb of the parabolic relationship) may be a result of historically limited immigration/recolonization of the thermally isolated Arctic deep-water basins that feed the cold-water flow through the Faroe-Shetland Channel. The bathymetric distribution of polychaetes and other benthos in this region appears to be intimately linked with the thermal regime, having a long-term impact (geological timescales) on the deep-water species pool and leading to local enhancement of diversity where cold- and warm-water masses meet and mix.     

Individual variation in feeding habitat use by adult female green sea turtles (Chelonia mydas): are they obligately neritic herbivores?

Satellite telemetry and stable isotope analysis were used to confirm that oceanic areas (where water depths are >200 m) are alternative feeding habitats for adult female green sea turtles (Chelonia mydas), which have been thought to be obligate herbivores in neritic areas (where depths are <200 m). Four females were tagged with satellite transmitters and tracked during post-nesting periods from Ogasawara Islands, Japan. Three females migrated to neritic habitats, while transmissions from another female ceased in an oceanic habitat. The overall mean nighttime dive depths during oceanic swimming periods in two females were <20 m, implying that the main function of their nighttime dives were resting with neutral buoyancy, whereas the means in two other females were >20 m, implying that they not only rested, but also foraged on macroplankton that exhibit diel vertical migration. Comparisons of stable carbon and nitrogen isotope ratios between 89 females and the prey items in a three-source mixing model estimated that 69% of the females nesting on Ogasawara Islands mainly used neritic habitats and 31% mainly used oceanic habitats. Out of four females tracked by satellite, two females were inferred from isotope ratios to be neritic herbivores and the two others oceanic planktivores. Although post-nesting movements for four females were not completely consistent with the inferences from isotope ratios, possibly due to short tracking periods (28–42 days), their diving behaviors were consistent with the inferences. There were no relationships between body size and the two isotope ratios, indicating a lack of size-related differences in feeding habitat use by adult female green turtles, which was in contrast with loggerhead sea turtles (Caretta caretta). These results and previous findings suggest that ontogenetic habitat shifts by sea turtles are facultative, and consequently, their life histories are polymorphic.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Palaeoenvironmental conditions preceding the Messinian Salinity Crisis: A case study from Gavdos Island

The Messinian pre-evaporitic sedimentary succession of Gavdos Island (Metochia section) is a nearly uninterrupted succession of marine sediments, dominated by finely laminated diatomaceous marls, which are cyclically alternating with clayey diatomites and white diatomites. The qualitative and quantitative analysis of the planktonic foraminiferal fauna allowed the recognition of nine bioevents, which have been astronomically dated for the Mediterranean. The base of the diatomitic succession in Gavdos Island is dated at 6.722 Ma and the top at 6.015 Ma. The studied section contains benthic foraminiferal genera characteristic of an outer shelf to slope environment. The qualitative and quantitative analysis of this microfauna revealed three benthic foraminiferal fossil assemblages and the occurrence of allochthonous species transported into the bathyal environment by current activity. The cyclical pattern of the benthic foraminifera assemblages indicates that the studied sediments have been affected by repeated episodes of basin restriction characterized by low diversity benthic foraminifera populations, and a limited planktonic foraminifer association typified by shallow, surface-dwelling forms. This restriction was partly due to Antarctic cooling, which produced palaeo-Mediterranean sea-level oscillations during the Early Messinian, as a prelude to closure of the Atlantic connections. The relative impact of climatic versus tectonic control on sedimentation patterns within this basin is discussed.     

Bioerosion along a bathymetric gradient in a cold-temperate setting (Kosterfjord, SW Sweden): an experimental study

In the cold-temperate setting of the Swedish Kosterfjord, a 2-year experiment was launched in order to assess bioerosion rates and to investigate the endolithic borer communities in relation to light availability (relative bathymetry), hydrography and exposure time. The inventory of microendolithic traces, studied by SEM analysis of epoxy resin casts of planted bivalve shells, yields diverse ichnocoenoses comprising a total of 21 traces produced by boring cyanobacteria (7), chlorophytes (4), fungi (6) and traces of uncertain affinity (4). The link between the endoliths (biotaxa) and the traces they leave (ichnotaxa) is evaluated by the study of the boring organisms in situ by transmission light microscopy of planted Iceland spar and bivalve shells. Additionally, the activity of various macroborers (foraminiferans, polychaetes, echinoids, gastropods and sponges) is documented, adding to a distinct diversity maximum at 7 m water depth. A highly condensed photic zonation, due to the high latitude (59°) and eutrophic conditions, is recorded by the measurement of the Photosynthetically Active Radiation (PAR) and is confirmed by the bathymetric range of the photic related ichnocoenoses. At 1 m water depth, a mature shallow euphotic ichnocoenosis dominated by cyanobacteria and at 7 m, a deep euphotic ichnocoenosis dominated by chlorophytes, respectively, is developed after as little as 12 months exposure. With the vanishing light availability from 15 m downwards, the ichnocoenoses development is significantly slowed and only immature dysphotic and aphotic borer communities (dominated by fungi) are encountered. Strong fluctuations of salinity (down to 8%) and temperature (0–20°C) in the euphotic zone indicate most phototrophs present to be considerably euryhaline and eurytherm, while most endolithic fungi appear preferentially in the deeper, more stable marine waters.     

Calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea: distribution patterns and influence of main environmental gradients

The distribution of calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea was quantitatively analysed. The samples contain 11 cyst species and the vegetative coccoid Thoracosphaera heimii. Cyst abundance increases towards the deeper parts of the basins and is generally higher in the eastern Mediterranean Sea. Three major distribution characteristics exist: (1) different assemblages in oceanic and neritic regions, (2) little agreement with the associations of areas studied so far like the Atlantic Ocean, and (3) a unique oceanic assemblage in the eastern Mediterranean Sea. A gradual change in cyst assemblages from the western to the eastern Mediterranean Sea was observed and statistically compared with the main environmental gradients in the upper water column. Temperature, nitrate concentration and possibly salinity appear to be the most important factors controlling cyst production. Three groups containing cysts with similar environmental preferences can be distinguished: (1) an eastern Mediterranean group related to relatively high temperature and salinity but low nitrate concentration, (2) a group of more or less consistently abundant cosmopolitan species tolerating or even preferring relatively low temperature and salinity but high nitrate concentration, and (3) a group containing species that are possibly adapted to neritic environments and have probably been transported from coastal areas into the studied regions. In contrast to other calcareous plankton, calcareous dinoflagellate cysts correlate strongly with the main environmental gradients in the Mediterranean Sea, bearing a high potential for palaeoenvironmental reconstructions.     

Composition, abundance and stratification of soft-bottom macrobenthos from selected areas of the Ross Sea shelf (Antarctica)

Composition, abundance and stratification of soft-bottom macrobenthos were studied at three selected sites on the Ross Sea shelf (Antarctica) with different geomorphology and sedimentation regimes. Sites A (southwest Ross Sea, 810 m depth) and B (Joides basin, 580 m depth) were characterized by biogenic mud and clay sediments, whereas site C (Mawson bank, 450 m depth) featured sandy sediments mixed with a conspicuous biogenic component characterized by shells and tests of calcareous invertebrates (mainly barnacles of the genus Bathylasma). The macrofauna of sites A and B was mainly composed of infaunal polychaetes and bivalves. The assemblages comprised both surface and sub-surface deposit feeders, including some conveyor-belt polychaetes (Maldanidae and Capitellidae) that are responsible for high sediment mixing and bioturbation. The macrobenthos of site C was dominated by crustaceans, polychaetes and echinoderms (ophiuroids), and mainly by filter feeders and epifaunal or interstitial forms. Abundances were higher (up to 1040 ind. m⁻²) at site B than at sites A and C (430 and 516 ind. m⁻², respectively). At sites A and B the benthos was mainly concentrated in the upper 5 cm of the sediment, and abundances declined sharply in the deeper sediment layers. These results indicate a high degree of consistency between sediment features and benthic community structure, which are both strongly related to local hydrography and bottom dynamics. Sites A and B represent areas where the organic input to the seafloor by vertical sedimentation from the upper water column is high. Site C, however, is characterized by high sediment instability and food particles advecting mainly horizontally. The community is more physically controlled by unpredictable, and probably frequent, disturbance events (e.g., bottom turbid currents, sediment reworking and displacement). Individuals were relatively small, indicating that probably they are not able to grow up to the adult size and reproduce. The community may be represented by “pseudopopulations” depending on the settlement of larvae invading from neighbouring areas. Accepted: 23 October 1998     

Fauna of Prosobranch Gastropods of Peter the Great Bay,Sea of Japan,and the Biogeographical Composition

The complete list of prosobranch gastropods comprising 195 species classified in 97 genera and 38 families was compiled for Peter the Great Bay (northwest of the Sea of Japan) and the adjacent water areas. In general, in the bay low boreal species prevail, which supported its assignment to the Manchurian (North Japanese, Sea of Japan, Asian) Low Boreal Pacific Subregion of the Boreal Pacific Region. Shallow water thermotropic species mostly prevailed in the littoral and upper sublittoral (to a depth of 50 m) zones of the bay; psychrotropic species were found in the lower sublittoral and upper bathyal (50–500 m) zones; and bathyal thermotropic species inhabited the lower (more then 500 m) bathyal zone.