The benthic foraminiferal communities of the northern Adriatic continental shelf

Off the Po Delta in the northern Adriatic, three different foraminiferal associations were identified in the fraction >0.125 mm of 25 sediment samples. The first association concerns sample stations between depths of 5 and 13.5 m in the shallow, nutrient-rich belt and is characterised by dominant Ammonia beccarii. The second occupies the 29.5–38.5-m-deep, nutrient-rich zone of clay-rich sediment, where inputs from the Po are concentrated, and is dominated by Nonionella opima. The third association, in the 21–46-m-deep and nutrient-poor zone, is dominated by Textularia agglutinans. The same distribution of communities was obtained using total associations (living and dead specimens) and biocenosis (stained individuals). The good correspondence with the foraminiferal distributions described in the past indicates that, in spite of the occurrence of anoxic and dysoxic events, the environmental state in the northern Adriatic may be considered stable.     

Polychaete distribution on the southwestern Atlantic continental shelf

Diversity and distribution of polychaetes on the southeastern Brazilian Shelf (SBS) adjacent to the city of Santos were studied. The study area is situated in the vicinity of Santos Bay with its estuarine complex and other small rivers along the coast. A total of 16,274 specimens belonging to 214 polychaete species were found at 21 sampling stations during two different periods. Two communities occur along the shelf and were related firstly to sediment characteristics. Prionospio dayi (Spionidae) was dominant in the inner shelf community that was characterized by well-sorted, very fine sand. The outer shelf community was found in muddy sediments with high organic matter content and was dominated by subsurface deposit feeders, like Petersenaspis capillata (Sternaspidae) and Leitoscoloplos kerguelensis (Orbiniidae), and by large carnivores such as Aglaophamus sp. (Nephtyidae) and Sigambra sp. (Pilargidae). A transition zone of mixed sediments presenting high diversity and richness was found between these communities. The characteristics of bottom water and food quality in the sediment were important to divide the inner shelf into two sub-areas. Nearshore sampling stations (A group) were more influenced by freshwater input, mainly during summer. This influence is not conspicuous at stations close to 30?m depth (B group). However the effect of South Atlantic Central Water mass (SACW) intrusion on the benthic system was observed on the inner shelf – B group during the summer. The summer intrusion of SACW onto the inner shelf may explain the higher quality of organic matter that resulted in an increase in polychaete abundance and richness.     

Facies distribution patterns of some marine benthic faunas in early paleozoic platform environments

Worldwide Late Cambrian—Silurian lithofacies patterns indicate that the platforms of that time were sites of accumulation of two essentially different rocks suites: the platform carbonate rocks and the platform terrigenous rocks. Most of the platform rocks accumulated as sediments in shallow marine environments similar to those of the present but far more widely spread.Present-day marine benthic faunas are distributed in depth zones which are primarily controlled by temperature. Faunas tend to occur in substrate-related discrete clusters (communities) within each life zone; similar substrates in different depth zones commonly have different faunal associations. Individual phyletic stocks may encounter environmental optimum or near-optimum conditions in certain areas, that commonly are revealed by an abundance of species and individuals within species in each stock. Environmental optimum conditions depend upon availability of food that may be utilized, modes of feeding of the animals present, water motion, and substrate, among other factors. Organisms in past seas were distributed in patterns similar to those of the present.Carbonate platforms were particularly widespread during the latest Cambrian—Early Ordovician. Intertidal environments spread widely across those platforms during that time and characteristic faunal associations developed in them. Saukiid and related tribolites dominated latest Cambrian carbonate platform intertidal faunas. The Early Ordovician carbonate platform intertidal was dominated by archeogastropod-nautiloid cephalopod faunas. These animals were joined by tabulate corals and certain brachiopods during the latter part of the Ordovician and Silurian as prominent faunal elements in the carbonate platform intertidal—shallow subtidal. Cruziana and related trace fossils, bivalves, and certain tribolites (notably homalonotids and dalmanitids) dominated most terrigenous platform intertidal—shallow subtidal faunas of the Ordovician and Silurian.Articulate brachiopods (primarily orthoids, strophomenoids, and rhynchonelloids) appear to have been relatively prominent during the Early Ordovician in shallow subtidal environments on both carbonate and terrigenous platforms and to have spread down the bathymetric gradient into increasingly deeper subtidal areas of both platforms during the latter part of the Ordovician. Tribolites dominated faunas in relatively moderate to deep subtidal environments on both platforms during the early part of the Ordovician. They were gradually replaced by brachiopods in first the shallower, and later the deeper subtidal as dominant members of the faunas. Brachiopods (primarily pentameroids and spiriferoids) dominated nearly all Silurian warm-water subtidal environments from the shallow subtidal to the edges of the platforms.Platform uplifts in the Middle Ordovician and glacio-eustatic sea-level fluctuations in the Late Ordovician caused environmental changes across the platforms that were accompanied by marked replacements among marine benthic faunas in all environments. The distribution of Ordovician carbonate platforms and glacial deposits suggests that an Ordovician polar region may have been close to present-day equatorial Africa and that Ordovician warm temperate-tropical regions lay close to the present-day North Pole.     

The measurement of marine species diversity, with an application to the benthic fauna of the Norwegian continental shelf

Species diversity includes two aspects, the number of species (species richness) and the proportional abundances of the species (heterogeneity diversity). Species richness and heterogeneity diversity can be measured over different scales; a single point, samples, large scales, biogeographical provinces and in assemblages and habitats. In the literature, the terminology of these scales is confused. Here, scales are given a uniform notation. Scales of species richness and heterogeneity diversity are distinguished from turnover (beta) diversity, which is the degree of change in species composition along a gradient. Methods of measurement of the scales of species richness, heterogeneity diversity, turnover diversity and for estimating total species richness are reviewed. Two methods for measuring heterogeneity diversity are recommended Exp H′ (where H′ is the Shannon-Wiener index) and 1/Simpson’s index, together with an equitability index J′. The reviewed methods are then applied to a data set from the Norwegian continental shelf to illustrate the advantages of the recommended methods. Finally, the application of the methods to assessment of effects of disturbance, to studies of gradients of species richness and to conservation issues are discussed.     

Spatial and temporal distribution of benthic Polychaeta from the continental shelf of Tamaulipas, Gulf of Mexico]

In three oceanographic cruises off southern Tamaulipas (May, July and November, 1992), a total of 102 sediment samples were collected by autonomous diving at depths of 2.5 to 20.5 m, with a cylindrical 4 liter acrylic tube. The samples were sieved (aperture size 0.5 and 1.0 mm). In total, 88 species of polychaete annelids were determined (33 families); 15 species are first records for Mexico and three for the Gulf of Mexico. The dominant species were Paraprionospio pinnata, Scoletoma verrilli, Ceratocephale oculata, Aricidea finitima, Apoprionospio pygmaea, Onuphis eremita oculata and Prionospio cristata; P. pinnata was the most abundant (14.4% of the total). Highest abundance and diversity of species was in May (63 species and 622 organisms), followed by July (48 species and 401 organism); November was lowest (47 species and 217 organisms). Most diversity and abundance were found in the sandy bottoms.     

Patterns of benthic mega-invertebrate habitat associations in the Pacific Northwest continental shelf waters

As human impacts and demands for ocean space increase (fisheries, aquaculture, marine reserves, renewable energy), identification of marine habitats hosting sensitive biological assemblages has become a priority. Epifaunal invertebrates, especially the structure-forming species, are an increasing conservation concern as many traditional (bottom-contact fishing) and novel (marine renewable energy) ocean uses have the potential to displace or otherwise impact these slow-growing organisms. The differences in mega-invertebrate species assemblages between high-relief rocks and low-relief sediments are well documented and likely hold for most marine environments. In anticipation of potential development of marine renewable energy faculties off Oregon and Washington (USA), a survey of the benthic invertebrate assemblages and habitats was conducted on the continental shelf of the Pacific Northwest, using video footage collected by ROV, to more finely characterize these assemblage–habitat associations. Four main associations were found: pure mud/sand dominated by sea whips and burrowing brittle stars; mixed mud–rock (which may be further divided based on size of mixed-in rocks) characterized by various taxa at small densities; consolidated rocks characterized by high diversity and density of sessile or motile mega-invertebrates; and rubble rocks showing less diversity and density than the consolidated rocks, possibly due to the disturbance generated by movement of the unconsolidated rocks. The results of this study will help classify and map the seafloor in a way that represents benthic habitats reflective of biological species assemblage distributions, rather than solely geological features, and support conservation and management planning.     

Influence of benthic macrofauna on microbial production of methylmercury in sediments on the New England continental shelf

Microbial methylation processes in sediment are an important source of toxic monomethylmercury (MMHg) to aquatic ecosystems. Although bioturbation activities (feeding, digging of galleries, excavations, bioirrigation) by benthic fauna are known to affect many biogeochemical processes, their influence on benthic MMHg production is poorly understood. We investigated the effect of benthic fauna on the microbial production of MMHg in sediments on the continental shelf of the northwest Atlantic Ocean in September 2009. Replicate cores of sieved (control) and unaltered sediment containing native macrofauna were incubated to examine the influence of benthic macrofauna on net MMHg production, potential gross rates of Hg methylation, sediment reworking, dissolved oxygen and organic carbon concentrations, and microbial metabolic activities. The presence of macrofauna stimulated aerobic microbial respiration and net MMHg production, but had no observed effect on short-term gross rates of Hg methylation. This suggests that bioturbation may promote net MMHg production by inhibiting demethylating microorganisms, although overall community metabolism was increased. Results from this work emphasize the need to enhance our knowledge and understanding of the interactions among benthic fauna, microorganisms, and geochemistry in affecting MMHg production.     

Distribution of recent benthic foraminifera in shelf carbonate environments of the Western Mediterranean Sea

The distribution of recent shallow-water benthic foraminifera in surface sediment samples from cool-water carbonate environments of the Oran Bight, Alboran Platform and Mallorca Shelf in the Western Mediterranean Sea was studied. Multivariate statistical analyses resulted in the identification of species assemblages, representing different environmental settings. In all three regions the assemblages show a distinct bathymetric zonation that is mainly attributed to the distribution of rhodoliths and related substrates, but also to water turbulence and the availability of food at the sea floor. The live assemblages (Rose Bengal stained individuals) are characterised by rather low diversity and low standing stocks, likely reflecting seasonal population dynamics. In the Oran Bight, elevated standing stocks of “high food”-taxa suggest the impact of anthropogenic eutrophication on the near-coastal benthic ecosystems of this area. The diversity of the dead assemblages is higher than in siliclastic shelf ecosystems of the Mediterranean Sea but lower when compared to carbonate environments of the Levantine Sea. This regional difference is mainly attributed to lower sea surface temperatures and the lack of Lessepsian invaders in the western Mediterranean Sea. In all study areas, a distinct faunal change occurs between approximately 80–90 m water depth. This change coincides with the lower distribution limit of living rhodoliths at the shelf of Mallorca, providing coarse-grained substrates that are dominated by attached taxa. Below this depth interval, the fauna shows regional differences depending on the grain-size and related accumulation of organic material. Fine-grained substrates with infaunal niches are restricted to low-energy environments on the deeper shelf southwest off Mallorca.     

Distribution of the twenty seven dominant species of shelf benthic foraminifers on the continental shelf, north of Dakar (Senegal)

One hundred and thirty-one samples were collected on the shelf and on the uppermost slope (down to 180 m) off Northern Senegal, between 14 °50′ and 16 °20′ N latitude.Two hundred and three species of benthic foraminifers were recognized. Most of them were reported in previous works, along the coast of Africa. Twenty seven species are selected for detailed analysis and distribution maps are given for each of them. Q mode and R mode statistical analyses were performed on these selected species. The distribution is mainly related to depth; the second factor of distribution is the nature of the sediments: about 30% of the study area is covered by the muddy sediments of the pro-delta of the Senegal river. Hierarchical analysis shows that the main limit in the pattern of change of these 27 species with depth is about 60–65 m.A depth index Di, calculated on the basis of twelve selected species, gives a depth indication with a precision of about 40 m over the shelf. It is possible to envisage a possible use of this index for the investigation of Quaternary sea-level changes.     

Patterns of benthic fauna and benthic respiration on the celtic continental margin in relation to the distribution of phytodetritus

In-situ and shipboard measurements of sediment community oxygen consumption (SCOC), in conjunction with a study of the distributions of macro and megafauna and phytopigments, were used to determine and, where possible, explain the distribution of labile particulate organic matter (POM) on the NE Atlantic continental slope (Goban Spur, SW Ireland). A specific issue concerned the existence of depocentres of labile POM on the slope caused by lateral transport, a phenomenon that has been found previously in the NW Atlantic. The SCOC data from October 1993 and May 1994 showed a steady decrease with increasing water depth. SCOC values ranged from 5.4 mmol m⁻² d⁻¹ at the shelfbreak to 0.3 mmol m⁻² d⁻¹ at 4,500 m depth. No evidence was found for seasonal variation in SCOC. A clear seasonal signal was observed with regard to sediment phytopigments and phytopigment fluxes into sediment traps attached to the benthic lander. The upper- and mid-slope values of both parameters were much higher in May 1994 than in October 1993 and August 1995. This is consistent with the normal spring bloom pattern; but because of the degraded state of the May phytodetritus in the near-bottom water, reflected in the lack of a response in SCOC and the low chlorophyll-a concentrations, it was concluded that the material was not derived from the overlying photic zone, but instead transported from elsewhere in the benthic nepheloid layer (BNL). In August 1995, the lower slope (>3,000 m) had received a strong and fresh phytodetritus pulse (3 g C m⁻²) forming a mucous layer on top of the sediment. Using phytopigments and sterols as molecular markers, it was shown that the pulse was derived from an offshore bloom with an important contribution by dinoflagellates. By contrast, no mucous layer was found on the upper slope stations in August 1995. Macrofauna biomass showed a distinct decline from the upper slope down to the lower slope conforming to the diminishing supply of labile POM. The total wet biomass of megafauna reached relatively high values at the lower slope (>3,500 m) owing to large motile sea cucumbers. The presence of these “vacuum-cleaner” sea cucumbers is considered indicative of the occurrence of phytodetritus pulses. In spite of their assumed adaptation to periodic pulses, the estimated contribution by the sea cucumbers to the total benthic mineralization is minor. When combining data from different years/seasons we observed decoupling between the food supply to the lower slope and the upper and mid slopes. The major pulse to the former comes from an offshore summer bloom. The upper and mid slope appear to be fuelled by spring bloom material which is subsequently redistributed on the upper slope in a BNL. The quality of the seston in the BNL diminished in the offshore direction as indicated by the phytopigment concentrations.     

Patterns of benthic mega-invertebrate habitat associations in the Pacific Northwest continental shelf waters: a reassessment

As human impacts and demands for ocean space increase (fisheries, aquaculture, marine reserves, renewable energy), identification of marine habitats hosting sensitive biological assemblages has become a priority. Epifaunal invertebrates, especially the structure-forming species, are an increasing conservation concern as many traditional (bottom-contact fishing) and novel (marine renewable energy) ocean uses have the potential to displace or otherwise impact these slow-growing organisms. The differences in mega-invertebrate species assemblages between high-relief rocks and low-relief sediments are well documented and likely hold for most marine environments. In anticipation of potential development of marine renewable energy faculties off Oregon and Washington (USA), a survey of the benthic invertebrate assemblages and habitats was conducted on three rocky reefs on the continental shelf of the Pacific Northwest, using video footage collected by remotely operated vehicle, to more finely characterize these assemblage–habitat associations. Benthic assemblages appeared to first group by depth (50–80 vs. 100–120 m), then by relief (consolidated rocks vs. unconsolidated rocks and soft sediments). Consolidated rocks were characterized at each site by a combination of various sponges, gorgonians, sea anemones and echinoderms; unconsolidated rocks were characterized at Grays Bank by sea anemones and burrowing brittle stars, and at Bandon-Arago by sponges and echinoderms; soft sediments were characterized at Grays Bank and Siltcoos Reef by sea whips and burrowing brittle stars, as well as pink shrimps and sea stars at Siltcoos Reef, and at Bandon-Arago by sponges, gorgonians and echinoderms. The results of this study will help classify and map the seafloor in a way that represents benthic habitats reflective of biological species assemblage distributions, rather than solely geological features, and support conservation and management planning.     

Filamentous bacteria inhabiting the sheaths of marine Thioploca spp. on the Chilean continental shelf

A new component of the benthic Thioploca mat microbial ecosystem on the Chilean continental shelf was detected by epifluorescence microscopy: filamentous, bacterial endobionts of 4–5-μm filament diameter and length sometimes exceeding 1 mm. These filaments were identified as growing within Thioploca sheaths located between the sediment surface and c . 5 cm depth. Their location coincided with maximal biomass and biovolume of Thioploca filaments in surficial sediments, and with maximal abundance and activity of sulfate-reducing bacterial populations near the sediment/water interface. FISH and environmental characteristics support the working hypothesis that these endobiont populations are members of the filamentous, sulfate-reducing bacterial genus Desulfonema . Found at several sampling stations over a decade-long interval (1994–2006), these populations appear to be a stable component of the Chilean Thioploca mat ecosystem.     

Distribution and abundance of demersal fishes and of some other marine benthic organisims on the continental shelf (0-60 m) of French Guiana

In order to establish the distribution and abundance of demersal fishes and of some other benthic organisms on the continental shelf of French Guiana (western central Atlantic), ninety-five bottom trawls were effected at depths ranging from 0 to 60 m in October 1993. A total of one hundred and ten different species were identified including eight decapod crustaceans, two cephalopods, one sea turtle and ninety-nine fishes. Despite the high species richness in benthic macrofauna, most species showed a low count, and only twelve of them comprised more than 80% of total captures. This study has mainly highlighted the existence of a well-pronounced bathymetric zonation. This phenomenon would appear to be linked to environmental factors, especially salinity and substrate granulometry, which are greatly conditioned by fresh water and sediment flowing in large rivers such the Amazon River. The results revealed three distinct faunistic assemblages: a littoral (or shallow-water) community (0-30 m) distributed in coastal estuarine waters characterized by muddy bottoms, a middle-shelf community (30-50 m), and a lower-shelf community (depths > 50 m) distributed in deeper marine waters characterized by sandy bottoms.     

Testing the predictive performance of distribution models

Distribution models are used to predict the likelihood of occurrence or abundance of a species at locations where census data are not available. An integral part of modelling is the testing of model performance. We compared different schemes and measures for testing model performance using 79 species from the North American Breeding Bird Survey. The four testing schemes we compared featured increasing independence between test and training data: resubstitution, random data hold‐out and two spatially segregated data hold‐out designs. The different testing measures also addressed different levels of information content in the dependent variable: regression R² for absolute abundance, squared correlation coefficient r² for relative abundance and AUC/Somer’s D for presence/absence. We found that higher levels of independence between test and training data lead to lower assessments of prediction accuracy. Even for data collected independently, spatial autocorrelation leads to dependence between random hold‐out test data and training data, and thus to inflated measures of model performance. While there is a general awareness of the importance of autocorrelation to model building and hypothesis testing, its consequences via violation of independence between training and testing data have not been addressed systematically and comprehensively before. Furthermore, increasing information content (from correctly classifying presence/absence, to predicting relative abundance, to predicting absolute abundance) leads to decreasing predictive performance. The current tests for presence/absence distribution models are typically overly optimistic because a) the test and training data are not independent and b) the correct classification of presence/absence has a relatively low information content and thus capability to address ecological and conservation questions compared to a prediction of abundance. Meaningful evaluation of model performance requires testing on spatially independent data, if the intended application of the model is to predict into new geographic or climatic space, which arguably is the case for most applications of distribution models.     

Bathymetric distribution of benthic foraminifera on the Australian-Irian Jaya continental margin,eastern Indonesia

We identified 164 taxa of benthic foraminifera in 35 selected box-core top samples collected on the Australian-Irian Jaya continental margin in waterdepths between 60 and 2119 m, along three systematically sampled transects across the Banda Arc. The bathymetric distribution pattern of the benthic foraminiferal faunas is related to the oceanographic situation of this area, where the watermasses of the Indian Ocean collide with the watermasses of the Pacific Ocean. With the results of cluster analyses and empirical depth-ranges of “isobathyal” taxa, four faunal depth-zones and four subzones can be distinguished:

• 1.(A) The Outer Shelf Biofacies (60–150 m), corresponding to the photic oxycline-zone of the Indonesian Surface Waters, and inhabited by a benthic foraminiferal association dominated by Amphistegina lessonii, Operculina ammonoides, Heterolepa dutemplei and various miliolids.
• 2.(B) The Upper Bathyal Biofacies (150–400 m), reflecting the aphotic, deeper Indonesian Surface Waters, dominated by Bolivina robusta, Heterolepa mediocris, Hanzawaia nipponica and Lenticulina spp. A major faunal break is situated at the lower boundary of this depth-zone.
• 3.(C) The Middle Bathyal Biofacies (400–1500 m), representing the Indonesian Intermediate Waters with minimum oxygen-contents, dominated by Bolivina robusta, Cassidulina carinata, Gavelinopsis lobatulus and Sphaeroidina bulloides. In this depth-zone many taxa occur with only limited depth-ranges, on which four subzones (C1–4) could be identified, allowing for a local (paleo)bathymetric resolution of a few hundred meters.
• 4.(D) The Lower Bathyal Biofacies (1500–2120 m) corresponds with the Indonesian Deep Waters. It is dominated by Pullenia bulloides and other cosmopolitan deep water indicators, such as Epistominella exigua, Laticarinina pauperata, Oridorsalis umbonatus and Planulina wuellerstorfi.

The sample fraction > 250 μm can be used to readily delineate the major faunal trends. Paleobathymetric resolution improves when the sample portion > 125 μm is used.     

A comparison between biotic indices and predictive models in stream water quality assessment based on benthic diatom communities

Diatoms are widely used in stream bioassessment due to their broad distribution, extraordinary variability and the ability to integrate changes in water quality. The indices Specific Polluosensitivity Index (SPI), standardized Biological Diatom Index (BDI), European Economic Community Index (CEC) and Generic Diatom Index (GDI), originally developed in France, are often applied in Portugal to evaluate stream ecological quality based on diatom communities. Alternatively, predictive models resulting from the comparison between the communities of the study site and those of a set of reference sites representing undisturbed or the best available conditions of a given region have been proposed as valuable methods for evaluating the ecological status of streams. In the present study, we applied the four above-mentioned widely used diatom-based indices (SPI, BDI, CEC and GDI) and a predictive model (MoDi) to 54 sites located in central Portugal to assess the sensitivity of the five methods to a range of anthropogenic disturbances cumulatively affecting streams and represented by 27 variables (e.g., organic enrichment, changes in morphology of the channels, integrity of the riparian corridor, land use in the catchment). The results were analyzed comparatively through Spearman correlations, Boxplots and Stepwise Discriminant Analysis. This study confirmed the sensitivity of diatoms to organic and nutrient contamination (showed by the MoDi, BDI, CEC and SPI) and revealed the importance of suspended solids (through the MoDi, GDI, and SPI). The relevance of modifications in land use to diatoms was shown by all methods applied, except for the GDI. The MoDI also revealed the importance of changes in the structure and morphology of the reach and the channel, like the construction of artificial walls or embankments and connectivity; the BDI also related its assessments with the riparian zone integrity; and the SPI was not useful in detecting morphological pressures. The GDI produced the most divergent assessments and was less effective in revealing the anthropogenic disturbances. The use of the predictive model (MoDi) is therefore a good method for the assessment of streams in central Portugal because it expresses a great diversity of quantitative and qualitative changes in freshwater systems reflected in the structure (species richness and abundance) of diatom communities.     

The distribution of living benthic foraminifera on the continental slope and rise off southwest Norway

Surface sediment samples taken by ? corer from 45 stations on the Norwegian continental margin and in the Norway Basin have been investigated for their benthic foraminiferal content. Unlike previous studies, the living benthic foraminiferal fauna was differentiated from empty tests comprising the foraminiferal death assemblage. Factor analysis of both the living and dead faunal data reveals six living species assemblages and five corresponding dead assemblages. The additional living assemblage is characterized by the arenaceous speciesCribrostomoides subglobosum that dominates between 1400 and 2000 m water depth, but is rare in the dead faunal data.Trifarina angulosa and, to a lesser extent,Cibicides lobatulus characterize the shallowest foraminiferal assemblage from 200 to 600 m water depth, where it is associated with strong bottom currents and warm, saline Atlantic water of the North Atlantic Drift. On the slope between 600 and 1200 m water depth, theMelonis zaandami Species Assemblage dominates, particularly in areas characterized today by rapid sedimentation of terrigeneous material. Between 1000 and 1400 m depth, where the slope is covered by fine grained, organic-rich, terrigeneous mud, the living foraminiferal assemblage is characterized byCassidulina teretis andPullenia bulloides. Below 1400 m, three foraminiferal assemblages are found:C. subglobosum is found from 1400 to 2000 m,Cibicidoides wuellerstorfi andEpistominella exigua predominantly live from 2000 to 3000 m water depth, and below 3000 m,Oridorsalis umbonatus andTriloculina frigida dominate the fauna.All of theElphidium excavatum tests found in this study and theCassidulina reniforme tests found above 500 m water depth were found to be reworked.Analysis of the sediment grain-size distribution and the organic carbon content in surface samples from the deepest stations suggest that the abundance ofC. wuellerstorfi andE. exigua is positively correlated to relatively coarse (caused by planktic foraminifera) and organic-rich sediments, whereas high frequencies ofO. umbonatus andT. frigida coincide with low organic carbon content. We suggest thatC. wuellerstorfi is adapted to deep-sea environments with relatively high food supply, tolerating relatively low interstitial water oxygen content, whereasO. umbonatus may tolerate lower food supply prefering well-oxygenated interstitial waters.     

Distribution of sponges on the Mauritanian continental shelf

Transect sampling on the continental shelf off the Banc d'Arguin, Mauritania, revealed a patchy distribution of sponge species and populations. Major sponge habitats are inshore coastal sandstone flats harbouring a diverse infaunal sponge fauna, and the moving substrate of shells of live gastropods or empty shells occupied by hermit crabs which harbour a numerically important but species-poor incrusting sponge fauna. The latter forms occur over most of the depth profile. Horizontal distribution of the sponges shows a distinct gap in species and numbers associated with a muddy bottom area where the sediment-rich Banc d'Arguin run-off is found. North and south of this gap the specific composition of the infaunal sponges is considerably different and this is explained as evidence for limitation of range extensions, notably of the southern sponge fauna, by the muddy area.