Live Benthic Foraminifera Research Articles

Biodeposit dispersion around a deep cage finfish farm in the Northern Persian Gulf

Due to increasing demand for food, intensive mariculture of finfish is a fast developing industry in the Iranian part of the Persian Gulf (PG). The environmental impacts of cage fish farming largely involve release of excessive organic matter (biodeposits). Careful monitoring of fish farms to avoid anoxia and bottom “dead zones” is an essential part of a sustainable mariculture industry.Monitoring data were collected for a fish farm north of Kish Island that had been in full operation for a period of one year. The data were then incorporated into a hydrodynamic model in order to estimate the quantity and dispersion pattern of biodeposits around the farm.Our results show that the farm had significant impacts on local environmental conditions, including water transparency, sulfide levels, and Eh values. Bottom water clarity near the cages was >15 NTU. Underneath the cages, sediment sulfide values are >800 μmole, Eh is usually -100 or less, and the sedimentation rate is 6.8 g/m2/day. The number of live benthic foraminifera near the cages was 4.5/10 g aliquot, as opposed to 20 at a control site.Numerical modeling, combined with data from sediment traps, shows that the farm “footprint” is much larger than the actual area of the farm, and is elongated by tidal currents. Considering the relatively short operation of the farm, it is already close to generating anoxic bottom conditions over a 2 km wide area. This can potentially impact the fragile habitats of the Persian Gulf. Continued expansion of net pen fish farms in sensitive areas such as the PG should be carefully monitored.

Live (stained) benthic foraminifera from the West-Gironde Mud Patch (Bay of Biscay, NE Atlantic): Assessing the reliability of bio-indicators in a complex shelf sedimentary unit.

Live (Rose Bengal stained) shelf foraminiferal faunas have been studied at seven stations located along a shore-open ocean transect between 39 and 69-m depth in the West-Gironde Mud Patch (WGMP) (Bay of Biscay, NE Atlantic) to understand how complex environmental conditions (e.g., organic matter, oxygenation, sedimentary facies) control their ecological patterns (i.e., diversity, faunal composition, standing stock, and microhabitats). To do so, the WGMP was sampled in August 2017, at the end of the succession of phytoplankton blooms occurring in spring and summer. This morpho-sedimentary unit is bathed by well-oxygenated bottom waters and characterized by clay-silt facies containing variably degraded phytodetritus and traces of terrestrial organic matter. Oxygen penetration depth within the sediment is less than 7 ± 3 mm, indicating efficient organic matter in-sediment mineralization by aerobic respiration. Foraminiferal richness (S) presents relatively moderate values ranging between 15 and 35 taxa. According to Shannon Index H’, foraminiferal diversity tends to increase with water depth. Accordingly, the relative contribution of Eggerelloides scaber, the dominant foraminiferal species at all stations, decreases with increased depth and decreased proximity to the coast. The shallowest station (Station 1, 39 m), closest to the shore, is characterised by E. scaber, Quinqueloculina laevigata and Ammonia beccarii, species typical of inner-shelf environments constrained by high-energy hydrodynamics and river discharge. Surficial sediments at Station 1 constitute of winnowed sands depleted in organic carbon. Towards the centre of the WGMP, where clay-silt facies contain variably degraded marine phytodetritus and terrestrial organic compounds, foraminiferal faunas are characterized by Bulimina aculeata, Ammonia falsobeccarrii, Nouria polymorphinoides and Nonionoides turgidus. Yet E. scaber remains the most dominant taxon. Deeper stations (>55 m depth) located at the distal part of the mud patch are dominated by B. aculeata, A. falsobeccarrii, N. polymorphinoides and E. scaber. Accompanying these taxa are Bulimina marginata, Rectuvigerina phlegeri, Nonion faba and Paracassidulina neocarinata, which are typical of mid- and outer-shelf ecosystems enriched in sedimentary organic matter.

Live benthic foraminifera in the Yellow Sea and the East China Sea: vertical distribution, nitrate storage, and potential denitrification

Benthic foraminifera were investigated to determine their vertical distribution, nitrate storage, and potential denitrification in the Yellow Sea (YS) and the East China Sea (ECS). The phytodetritus content and freshness as well as sediment redox conditions were key factors determining the vertical distribution of foraminifera in sediments of the YS and the ECS. The intracellular nitrate (ICNO3) concentrations of Nonionella stella, Hanzawaia nipponica, Bolivina robusta, Cancris auriculus, and Globobulimina pacifica ranged from 3 to 114 mM, which in some cases was several hundred-fold more than the pore water nitrate (PWNO3) concentrations. The genus Hanzawaia was for the first time reported to store ICNO3 (316 +/- 73 pmol ind.(-1); 11 +/- 3 mM). The significant correlation between the ICNO3 concentration and foraminiferal abundance (Pearson correlation: r = 0.401, p < 0.01, n = 60) suggested that foraminifera may have an important role in nitrate storage in the sediments. The foraminiferal intracellular nitrate (FINO3) pool ranged from 9 to 74% of the ICNO3 pool in sediments, indicating that nitrate may be stored by other sediment organisms (e.g. diatoms). The chlorophyll a concentration, chloroplastic pigment equivalents (CPE), and chlorophyll a:phaeopigment ratio were all significantly positively correlated with the ICNO3 concentration (Pearson correlation: r = 0.563, 0.603, and 0.457, respectively; p < 0.01; n = 60), indicating that phytodetritus (e.g. diatoms) might also contribute to sedimentary ICNO3. Potential foraminiferal denitrification rates ranged from 9 to 92 mu mol m(-2) d(-1) in the YS and the ECS, indicating that benthic foraminifera might play a role in sedimentary denitrification.

Microhabitat preferences of live benthic foraminifera and stable carbon isotopes off SW Svalbard in the presence of widespread methane seepage

Abstract To constrain the use of, and better calibrate benthic foraminiferal carbon-isotope based proxies (δ13C) we analyzed live (Rose Bengal stained) benthic foraminifera from fjords, outer shelves, and the upper continental slope of SW-Svalbard. We further investigated whether the presence of widespread methane seepage altered benthic foraminiferal δ13C. The one-to-one relationship between the δ13C of Cibicidoides wuellerstorfi and Cibicides lobatulus tests and the δ13CDIC of bottom water in Nordic Seas was reconfirmed. We also confirmed an almost constant δ13C of live specimens of infaunal species Melonis zaandamae, Nonion labradoricum, and Globobulimina affinis independent of their subbottom sampling depth and pore water δ13CDIC at any given site. This is in contrast to the wide range of intraspecific δ13C values of both, epifaunal as well as infaunal species, observed between sites. We did not find significant correlations between foraminiferal δ13C minus site-specific δ13CDIC (Δδ13CFor − DIC) of the investigated species and the total organic carbon (TOC) contents of surface sediments. On the contrary, a distinct relationship is observed between high marine organic carbon (MOC) contents and low Δδ13CFor − DIC values of N. labradoricum and, to a lesser extent, G. affinis. These findings are important because on the one hand they confirm a systematic influence of the availability of labile MOC on deep infaunal species δ13C, whereas on the other hand they document the independence of epifaunal and infaunal species δ13C of TOC contents in well-ventilated bottom water and organic-rich surface sediment. Generally, species' mean δ13C reflects their average living depths (ALD5) such that epifaunal and shallow infaunal species depict highest, and deep infaunal species, lowest δ13C values. Mean Δδ13CFor − DIC values of neither epifaunal C. lobatulus and C. wuellerstorfi (− 0.05 ± 0.06‰) nor of infaunal M. zaandamae (− 2.40 ± 0.07‰), N. labradoricum (− 2.69 ± 0.13‰), and G. affinis (− 3.48 ± 0.15‰) seem to be significantly influenced by strongly elevated methane concentrations in the water column, widespread gas seepage at the sea floor, and low pore-water δ13CDIC; the latter possibly partly due to methanotrophic oxidation. The δ13C values of deep infaunal N. labradoricum and G. affinis minus epifaunal δ13C values (Δδ13CNlab − Cib and Δδ13CGaff − Cib), seem to decrease with increasing TOC and MOC contents. However, only the Δδ13CNlab − Cib values correlate significantly with MOC contents and thus marine primary productivity. Dissolved oxygen concentrations, estimated on the basis of Δδ13CGaff − Cib values, of > 230 μmol/kg are in accordance with reported well-oxygenated bottom water conditions at all stations.

Lateral and vertical distributions of living benthic foraminifera off the Douro River (western Iberian margin): Impact of the organic matter quality

Abstract In this study, we assess the impact of the quantity and quality of the organic matter on the distribution of live benthic foraminifera on a cross-margin transect off the Douro River (western Iberian margin). Surface sediments from five stations ranging from 50 to 2000 m water depth were collected in March 2011 at the end of the period of maximal river runoff, in order to better evaluate the importance of terrestrial input. Living (stained) benthic foraminiferal assemblages (> 150 μm) and environmental parameters (grain size, total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ 13 C TOC , pigments and amino acids) were investigated. Organic matter amounts follow the sediment grain size pattern with higher concentration in fine sediments and seem to control faunal density, except at the shallowest station where TOC is low and faunal density high. At this coastal site, a massive sandy deposit is identified and associated with very low faunal diversity. Labile organic matter is richest at the shelf stations where benthic foraminifera standing stocks are high. This is particularly evident on the Douro mud patch where both density and diversity are high. Foraminiferal faunas living at the shelf stations are dominated by species (e.g., Nonion scaphum , Ammonia beccari , i Bulimina aculeata and Eggerella scabra ) characteristic of the rich trophic conditions, with organic matter of mixed estuarine and marine origin. Very low total standing stocks on the upper slope are associated with coarse sediments, probably resulting from intense bottom currents at this depth resulting in poor trophic conditions. Deeper environments are characterized by species (e.g., Hoeglundina elegans , Uvigerina mediterranea and Reophax scorpiurus ) indicative of fairly abundant but low-quality organic matter. Finally, the faunal differences between the shelf stations may reflect different successional stages: an early stage at 50 m water depth where unstable conditions are observed, with faunas dominated by opportunistic species and a more mature fauna in the mud patch where more stable conditions prevail.

Live (Rose Bengal stained) foraminiferal faunas from the northern Arabian Sea: faunal succession within and below the OMZ

Abstract. Live (Rose Bengal stained) benthic foraminifera from the Murray Ridge, within and below the northern Arabian Sea oxygen minimum zone (OMZ), were studied in order to determine the relationship between faunal composition, bottom water oxygenation (BWO), pore water chemistry and organic matter (organic carbon and phytopigment) distribution. A series of multicores were recovered from a ten-station oxygen (BWO: 2–78 μM) and bathymetric (885–3010 m depth) transect during the winter monsoon in January 2009. Foraminifera were investigated from three different size fractions (63–125 μm, 125–150 μm and &gt;150 μm). The larger foraminifera (&gt;125 μm) were strongly dominated by agglutinated species (e.g. Reophax spp.). In contrast, in the 63–125 μm fraction, calcareous taxa were more abundant, especially in the core of the OMZ. On the basis of a principal components analysis, three foraminiferal groups were identified and correlated to the environmental parameters by canonical correspondence analysis. The faunas from the shallowest stations, in the core of the OMZ (BWO: 2 μM), were composed of "low oxygen" species, typical of the Arabian Sea OMZ (e.g. Rotaliatinopsis semiinvoluta, Praeglobobulimina sp., Bulimina exilis, Uvigerina peregrina type parva). These taxa are adapted to the very low BWO conditions and to high phytodetritus supplies. The transitional group, typical for the lower part of the OMZ (BWO: 5–16 μM), is composed of species that are tolerant as well to low-oxygen concentrations, but may be less critical with respect to organic supplies (e.g. Globocassidulina subglobosa, Ehrenbergina trigona). Below the OMZ (BWO: 26–78 μM), where food availability is more limited and becomes increasingly restricted to surficial sediments, cosmopolitan calcareous taxa were present, such as Bulimina aculeata, Melonis barleeanus, Uvigerina peregrina and Epistominella exigua. Miliolids were uniquely observed in this last zone, reflecting the higher BWO and/or lower organic input. At these deeper sites, the faunas exhibit a clear succession of superficial, intermediate and deep infaunal microhabitats, which can be linked to the deeper oxygen and nitrate penetration into the sediment.

Live (stained) benthic foraminifera from the Cap-Ferret Canyon (Bay of Biscay, NE Atlantic): A comparison between the canyon axis and the surrounding areas

Living (Rose Bengal stained) benthic foraminiferal faunas were investigated at 13 deep-sea stations sampled in the Cap-Ferret Canyon area (NE Atlantic). One station (151m) is located on the continental shelf close to the canyon head. All other stations are located along 2 bathymetric transects: 7 sites along the canyon axis with depths ranging from 300 to 3000m and 5 stations along the adjacent flank with depths ranging from 300m to 2000m. Sedimentological analyses indicate that the Cap-Ferret Canyon is at present inactive in terms of sediment gravity flow. Compared to stations on the adjacent flank, canyon-axis stations are generally characterised by shallow oxygen penetration depths, high diffusive oxygen uptakes (DOU) and high lipid contents. Higher mineralisation rates recorded in the canyon axis are likely due to a preferential focusing of labile organic matter in the canyon axis. Foraminiferal standing stocks do not exhibit any straightforward correlation with the different descriptors of organic matter available in the sediment. However, foraminiferal standing stock and diversity along the canyon axis are generally higher than on the adjacent flank. Canyon axis sites yield dominant species that are similar to those at adjacent flank and open slope stations located at comparable water depths. However, intermediate and deep infaunal species were only recorded in the lower canyon axis, where high amounts of organic matter were observed in deeper sediment layers. Finally, the faunal composition in the Cap-Ferret Canyon is different compared to the nearby Cap-Breton Canyon, where sediment gravity flows are active. The absence of pioneer species and the occurrence of highly specialized taxa are both consistent with the much more stable conditions in terms of hydro-sedimentary conditions prevailing in the Cap-Ferret Canyon.

Changes in distribution of calcareous benthic foraminifera in the central Barents Sea between the periods 1965–1992 and 2005–2006

Live benthic foraminifera assemblages from 30 surface sediment samples taken in 2005 and 2006 from the central Barents Sea are compared with total benthic foraminifera assemblages from a database containing samples taken between 1965 and 1992. We evaluate the hypothesis that observed environmental changes in the region have led to observable shifts in benthic foraminiferal fauna. Of the 12 infaunal calcareous species studied marked decreases were observed in cold water species Buccella spp., Elphidium excavatum, Islandiella norcrossi and Nonionellina labradorica. A decline combined with a marked change in spatial distribution is seen in Cassidulina laevigata, Trifarina fluens, Stainforthia loeblichi, Cassidulina reniforme, Cassidulina neoteretis, Melonis barleeanus, and Pullenia bulloides. Warm water species Epistominella nipponica is the only species of these 12 that increased in abundance. The general shift toward dominance of warm water species and temperature tolerant species agrees well with the observed temperature increase in the basin. At the level of individual data points, a relationship between assemblage change and environmental change is not straightforward. The comparison of the new data with the database also displays a shift toward higher abundances of more fragile species, which can be attributed to method differences. The species that display the most pronounced change are those associated with cold water and proximity of the ice edge.The magnitude of benthic foraminiferal change in the study area is largest in a conspicuous belt that appears to follow roughly the Polar Front. This area has a lower temperature and salinity gradient through the last decades than the rest of the study area, and its high faunal change may be due to the position of the Polar Front moving away from this area, and associated changes in the sea ice edge.

Intra-Annual Variation of Modern Foraminiferal Assemblage in a Tropical Mangrove Ecosystem in India

This study relates the abundance of foraminifera with the fluctuations in hydrobiological characteristics generated by the monsoonal cycle in a tropical mangrove ecosystem. Monthly variation of physicochemical properties of water and sediment, phytoplankton production, foraminiferal assemblages were measured in the littoral zone of the Sundarbans mangrove forest. Intra-annual variation of foraminifera exhibited a maximum abundance during the post-monsoon period and out of the 25 genera, numbers of calcareous and agglutinated forms were 16 and 9, respectively. Live benthic foraminifera were found to inhabit a wide range of sediment depths and inhabiting a high energy environment their abundance was not restricted to the uppermost centimeter. Owing to mechanical damage (due to high energy system), chemical dissolution and intense bioturbation, the taphonomic processes in this mangrove swamp could result in the destruction of the small size fraction of foraminifera, including agglutinated tests. The low numbers of agglutinated foram could be due to silty clay substrate. Abundance of more calcareous dead specimens over live ones could be attributed to predation and transportation of dead marine species. Most of the marine species could not survive in this freshwater dominated system. Anthropogenic nutrient input and diatom bloom in association with enhanced food to benthos are important controlling factors on foraminiferal abundance and composition.

Strong thermodynamic imprint on Recent bottom-water and epibenthic δ13C in the Weddell Sea revealed: Implications for glacial Southern Ocean ventilation

Paleonutrient proxies are widely used to reconstruct the geometry of deep-water masses during the Last Glacial Maximum (LGM). Epibenthic δ13C provides best spatial coverage, and artifacts are well investigated. Discrepancies between reconstructed LGM-circulation patterns derived from models or different benthic nutrient proxies can partly be resolved by varying air–sea signatures of δ13C, i.e. δ13Cas. However, there are very few data available to calculate a δ13Cas of modern bottom water dissolved inorganic carbon (DIC) δ13C, and to document how this signal is recorded in benthic foraminiferal δ13C. Here I show that today bottom water in the Atlantic sector of the Southern Ocean is 13C enriched with δ13CDIC values between 0.4 and 1.0‰ and δ13Cas values >0.4‰, and that this signal is recorded in live and dead epibenthic δ13C. This is in contrast to a uniform modern Antarctic circumpolar δ13CDIC of rather 0.4‰, which hitherto is used as modern framework to compare to low LGM δ13CDIC of southern sourced bottom-water and glacial inter basin differences. I conclude that a potential reduction of the strong Recent thermodynamic imprint during bottom-water generation in glacial times could explain depleted circum Antarctic 13CDIC without associated CO2 enrichment and anoxia in Antarctic bottom waters. The present synoptic compilation of δ13CDIC and live benthic foraminifera δ13C is in support of hypotheses that explain low LGM δ13C by a depletion of southern end-member 13CDIC due to extensive sea-ice formation with low δ13Cas-brine rejection and diminished air–sea gas exchange.

LIVE BENTHIC FORAMINIFERAL FAUNAS ALONG A BATHYMETRICAL TRANSECT (282-4987 M) ON THE PORTUGUESE MARGIN (NE ATLANTIC)

Live benthic foraminifera were studied in eight cores collected along a depth transect ranging 282-4987 m on the Portuguese margin. Total standing stocks (TSS) and species assemblages from both 63-150- and >150-mu m fractions are compared between stations along the transect and with previous live foraminiferal studies from the Bay of Biscay and western Iberian margin. Based on the sedimentary organic matter contents and ecological traits of the retrieved foraminifera, three groups of stations are distinguished: (1) eutrophic upper-slope stations (282-1002 m) with faunas dominated by Uvigerina mediterranea, U. elongatastriata, Melonis barleeanus, Bigenerina nodosaria, Trifarina bradyi, Epistominella vitrea, Cribrostomoides bradyi, and Bolivina robusta, (2) mesotrophic middle- to lower-slope stations (1374-2475 m) with faunas dominated by Uvigerina peregrina, Globobulimina affinis, and Repmanina charoides, and (3) oligotrophic lower-slope and abyssal-plain stations (2908-4987 m) with faunas in the larger size fraction dominated by Cibicides kullenbergi and agglutinated species such as Reophax fusiformis and Recurvoides sp. 1. The smaller size fraction is dominated by opportunistic calcareous species such as Bulimina translucens, Epistominella exigua, and Nuttallides pusillus, along with Reophax fusiformis, but most of these species are diminished at 4987 m, where Reophax fusiformis, Pullenia salisburyi, and various monothalamous agglutinates are dominant. This succession of assemblages probably reflects the increasing scarcity of trophic resources with water depth. This hypothesis is corroborated by 1) the clear decrease of TSS with increasing water depth, and 2) the decreasing sediment phytopigment concentrations towards deeper sites. Moreover, the decreasing percentage of perforate calcareous foraminifera, and increasing percentage of agglutinated foraminifera with water depth, suggests that, in general, perforate calcareous species have higher trophic requirements than agglutinated ones.

Technical Note: Determination of the metabolically active fraction of benthic foraminifera by means of Fluorescent In Situ Hybridization (FISH)

Abstract. Benthic foraminifera are an important component of the marine biota, but protocols for investigating their viability and metabolism are still extremely limited. Classical studies on benthic foraminifera have been based on direct counting under light microscopy. Typically, these organisms are stained with Rose Bengal, which binds proteins and other macromolecules, but does not allow discrimination between viable and recently dead organisms. The fluorescent in situ hybridization technique (FISH) represents a new and useful approach to identify living cells possessing an active metabolism. Our work is the first test of the suitability of the FISH technique, based on fluorescent probes targeting the 18S rRNA, to detect live benthic foraminifera. The protocol was applied on Ammonia group and Miliolids, as well as on agglutinated polythalamous (i.e., Leptohalysis scottii and Eggerella scabra) and soft-shelled monothalamous (i.e., Psammophaga sp. and saccamminid morphotypes) taxa. The results from FISH analyses were compared with those obtained, on the same specimens assayed with FISH, from microscopic analysis of the cytoplasm colour, presence of pigments and pseudopodial activity. Our results indicate that FISH targets only metabolically active foraminifera, and allows discerning from low to high cellular activity, validating the hypothesis that the intensity of the fluorescent signal emitted by the probe is dependent upon the physiological status of cells. These findings support the usefulness of this molecular approach as a key tool for obtaining information on the physiology of living foraminifera, both in field and experimental settings.

Estudo multidisciplinar (geoquímica e associações de foraminíferos) para caracterizar e avaliar intervenções antrópicas na Baía do Araçá, Canal de São Sebastião, SP

The goal of this study was to assess possible human-induced changes in the environment due to the discharge of domestic sewage into the Araca Bay, Sao Sebastiao Channel, Sao Sebastiao, Brazil. In order to achieve this goal, in April 2006, we conducted grain size and geochemical (Toc, N, S, and P) analysis and determined the assemblage composition and distribution of live benthic foraminifera from shallow marine sediments collected around diffusers of the domestic sewage submarine outfall at the Araca Bay. Results showed that the area studied is a lithoclastic shallow environment with predominance of sandy sediments. However, in the northeastern area of the sampling grid, it was observed high concentrations of fine sediments (silt plus clay), with significant Toc (>; 1%), N (>; 0.2%) and S (0.3%) contents. The organic enrichment is inferred based on the phosphorus and sulphur contents, as well as on the oxidation-reduction potential, which was inferred using the Eh values and C/S ratios. In relation to the benthic foraminiferal assemblages, low richness was observed and the association is mainly composed of infaunal and detritivore species. There is a high abundance of Epifaunal species, which are bioindicators of well-oxygenated environments, in stations with no impact of the sewage discharged by submarine outfall. The occurrence of medium and small-sized foraminifera shells is qualitatively associated with low oxygen concentrations at the sediment-water interface. The dominance of a few species, especially Ammonia tepida, may indicate environmental stress.

BENTHIC FORAMINIFERA IN A LARGE INDO-PACIFIC CORAL REEF AQUARIUM

Live (rose Bengal-stained) benthic foraminifera were studied from one of the largest coral reef aquaria in the world (Burgers’ Ocean, Arnhem, the Netherlands). Benthic foraminifera were unintentionally transported to the aquarium with live rock (i.e., natural reef substratum) from Java and Bali (Indonesia) during initial setup in 2000. After eight years and stabilization of the water chemistry, the foraminifera were found to have successfully colonized this artificial environment. Fifty benthic foraminiferal taxa (>125 μm) were identified in samples from the various subenvironments within the aquarium. The ecological conditions in the aquarium appeared to be optimal for both symbiont-bearing foraminifera and hermatypic corals. Among the four symbiontic foraminiferal species identified, Heterostegina depressa was the most abundant and it was dominant in all samples. Overall, foraminiferal densities in the aquarium were relatively high compared to those in the natural environment emulated. Although foraminifera are not generally recognized as inhabitants of saltwater aquaria, they can play an important ecological role in this type of closed environment.

Live (stained) benthic foraminifera from the Rhône prodelta (Gulf of Lion, NW Mediterranean): Environmental controls on a river-dominated shelf

In this paper, we investigate the ecology of live (rose Bengal stained) benthic foraminifera collected at 20 stations ranging from 15 to 100 m depth in the Rhône prodelta (Gulf of Lions, NW Mediterranean). These sites were sampled in September 2006, five months after the Rhône River annual flood. Statistical analyses based on foraminiferal communities (> 150 μm) divide our study area into six main biofacies directly related to environmental conditions. Miliolid species are abundant in the relict prodeltaic lobe which is characterised by sand with low organic matter content. Close to the river mouth, the limited oxygen penetration in the sediment combined with important hydro-sedimentary processes constitute stressful conditions for foraminiferal faunas dominated by opportunistic species (e.g. Leptohalysis scottii). With increasing distance from the river mouth, foraminiferal faunas (e.g. Nonionella turgida, Eggerella scabra) adapted to thrive in sediments enriched in Rhône-derived organic matter under more stable hydro-sedimentary conditions appear. In the distal part of the Rhône River influence, benthic species (e.g. Valvulineria bradyana, Textularia agglutinans) living in fine sediment enriched in both continental and marine organic compounds emerge. At the deepest stations located in the south-eastern part of our study area, benthic foraminiferal faunas (e.g. Bulimina aculeata, Melonis barleeanus, Bigenerina nodosaria) are highly diverse, underlining stable environmental conditions characterised by marine-derived organic matter supplies and relatively deep oxygen penetration depth in the sediment. We also compare foraminiferal faunas sampled in September 2006 with communities sampled in June 2005, one month after the Rhône River annual flood ( Mojtahid et al., 2009). This comparison suggests that opportunistic species (e.g. B. aculeata, Cassidulina carinata, V. bradyana) have responded to organic matter inputs related to marine primary production in June 2005.

Ontogenetic effects on stable carbon and oxygen isotopes in tests of live (Rose Bengal stained) benthic foraminifera from the Pakistan continental margin

Abstract We determined the stable oxygen and carbon isotopic composition of live (Rose Bengal stained) tests belonging to different size classes of two benthic foraminiferal species from the Pakistan continental margin. Samples were taken at two sites, with water depths of about 135 and 275 m, corresponding to the upper boundary and upper part of the core region of the oxygen minimum zone (OMZ). For Uvigerina ex gr. Uvigerina semiornata and Bolivina aff. Bolivina dilatata, δ13C and δ18O values increased significantly with increasing test size. In the case of Uvigerina ex gr. U. semiornata, δ13C increased linearly by about 0.105‰ for each 100-μm increment in test size, whereas δ18O increased by 0.02 to 0.06‰ per 100 μm increment. For Bolivina aff. B. dilatata the relationship between test size and stable isotopic composition is better described by logarithmic equations. A strong positive linear correlation is observed between δ18O and δ13C values of both taxa, with a constant ratio of δ18O and δ13C values close to 2:1. This suggests that the strong ontogenetic effect is mainly caused by kinetic isotope fractionation during CO2 uptake. Our data underline the necessity to base longer δ18O and δ13C isotope records derived from benthic foraminifera on size windows of 100 μm or less. This is already common practice in down-core isotopic studies of planktonic foraminifera.

Analysis of foraminifera assemblages and sediment geochemical properties to characterise the environment near Araçá and Saco da Capela domestic sewage submarine outfalls of São Sebastião Channel, São Paulo State, Brazil

Superficial bottom samples were collected near diffusers of domestic sewage submarine outfalls at Araçá and Saco da Capela, São Sebastião Channel, Brazil. The goal of this study was to investigate the distribution and composition of live benthic foraminifera assemblages and integrate the results obtained with geochemical analyses to assess human-induced changes. According to the results obtained no environmental stress was observed near the Saco da Capela submarine outfall diffusers. The foraminifera assemblage is characterised by species typical of highly hydrodynamic environments, with well-oxygenated bottom waters and low nutrient contents. In contrast, near Araçá submarine outfall, organic enrichment was denoted by high phosphorus, sulphur and, to a lesser extent, total organic carbon content. Harmful influences on foraminifera could be identified by low richness and specific diversity, as well as the predominance of detritivore feeder species, which are associated with higher organic matter flux and low oxygen in the interstitial pore water.

Carbon and oxygen isotope geochemistry of live (stained) benthic foraminifera from the Aleutian Margin and the Southern Australian Margin

Comparisons of ambient bottom-water geochemistry and stable isotopic values of the tests of living (stained) calcareous benthic foraminifera from the North Pacific (on the Aleutian Margin, water depth 1988 m) and Murray Canyons group in the Southern Indian Ocean (Australian Margin, water depths 2476 m and 1634 m) provide modern environmental analogs to calibrate paleoenvironmental assessments. Consistent with the hypothesis that microhabitat preferences influence foraminiferal isotopic values, benthic foraminifera from both margins were depleted in 13C with respect to bottom-water dissolved inorganic carbon (DIC). The carbon isotope values of deep infaunal foraminifera ( Chilostomella oolina, Globobulimina pacifica) showed greater differences from estimates of those of DIC than shallow benthic foraminifera ( Bulimina mexicana, Bolivinita quadrilatera, Pullenia bulloides). This study provides new isotopic and ecological information for B. quadrilatera. The mean Δ δ 13C value, defined as foraminiferal δ 13C values minus estimated ambient δ 13C values from the Aleutian Margin, is 0.97‰ higher for G. pacifica than the mean from the Murray Canyon. This difference may result either from genetic or biological differences between the populations or from differences in environmental isotopic influences (such as pore water differences) that were not accounted for in the equilibrium calculations. These analyses provide calibration information for the evaluation of bottom water conditions and circulation patterns of ancient oceans based on fossil foraminiferal geochemistry.

Living benthic foraminifera of the Okhotsk Sea: Faunal composition, standing stocks and microhabitats

Live (Rose Bengal stained) benthic foraminifera were investigated in surface sediment samples from the Okhotsk Sea to reveal the relationship between faunal characteristics and environmental parameters. Live benthic foraminifera were quantified in the size fraction > 125 µm in the upper 8 cm of replicate sediment cores, recovered with a multicorer at five stations along the Sakhalin margin, and at three stations on the southwestern Kamchatka slope. The stations are from water depths between 625 to 1752 m, located close or within the present Okhotsk Sea oxygen minimum zone, with oxygen levels between 0.3 and 1.5 ml l - 1 . At the high-productivity and ice-free Kamchatka stations, live benthic foraminifera are characterized by maximal standing stocks (about 1700-3700 individuals per 50 cm 2), strong dominance of calcareous species (up to 87-91% of total live faunas), and maximal habitat depths (down to 5.2-6.7 cm depth). Vertical distributions of total faunal abundances exhibit a clear subsurface maximum in sediments. At the Sakhalin stations, which are seasonally ice-covered and less productive, live benthic foraminifera show lower standing stocks (about 200-1100 individuals per 50 cm 2), lower abundance of calcareous species (10-64% of total live faunas), and shallower habitat depths (down to 2.5-5.4 cm depth). Faunal vertical distributions are characterized by maximum in the uppermost surface sediments. It is suggested that 1) lower and strongly seasonal organic matter flux, caused by the seasonal sea ice cover and seasonal upwelling, 2) lower bottom water oxygenation (0.3-1.1 ml l - 1 ), and 3) more pronounced influence of carbonate undersaturated bottom water along the Sakhalin margin are the main factors responsible for the observed faunal differences. According to species downcore distributions and average living depths, common calcareous species were identified as preferentially shallow, intermediate and deep infaunal. Foraminiferal microhabitat occupation correlates with the organic matter flux and the depth of the oxygenated layer in sediments.

The influence of a simulated diatom bloom on deep-sea benthic foraminifera and the activity of bacteria: A mesocosm study

Live benthic foraminifera were collected from the Portuguese continental margin from 900 m water depth. Under controlled laboratory conditions, Thalassiosira pseudonana, was used to create an artificial diatom bloom. Two different diatom loads, high (240 μg C/cm 2) and low (80 μg C/cm 2) load, were fed to benthos. The response of the benthic foraminifera, total standing stocks (63–150 μm, >150 μm size fractions) and vertical distribution in the sediment, was analysed at 28 and 56 days following the simulated food pulse. The treated cores, or mesocosms, were compared to controls that were harvested at the experimental setup, prior to the feeding, and at the end of the experiment. Bacterial activity was assessed in terms of benthic nitrate and ammonium fluxes across the sediment–water interface. Prior to the simulated diatom bloom the total standing stocks of foraminifera declined significantly. The population recovered following the feeding and, especially under the higher diatom load, increased in comparison to the control cores. In general, a ‘two-phased’ response was measured in different size classes of foraminifera. An increase in the smaller-sized (63–150 μm) subpopulation was followed by an increase in the larger-sized (>150 μm) subpopulation. Elevated effluxes of ammonium were measured following the simulated diatom bloom. The highest effluxes were seen in the high-load treatment, reflecting the highest remineralised carbon load. The ammonium effluxes normalised to control levels around 25 days after the bloom. In addition, high effluxes of nitrate were measured, indicating enhanced nitrification following the diatom deposition. The nitrate effluxes normalised to control levels around 40 days after the feeding event. Several foraminiferal taxa, e.g. Melonis barleeanum, Bigenerina cylindrica, Chilostomella oolina, responded to the diatom bloom (or increased bacterial activity) and increased in numbers. However, the vertical distribution of these infaunal species was not influenced by the added food. Only two infaunal species, Pullenia sp. and Trochammina sp., were observed to increase in numbers in the surficial sediments. These two taxa most likely migrated to the surface to consume the labile organic matter. In contrast, the other infaunal species perhaps benefited from the diatom bloom indirectly, e.g. from increased bacterial activity in the sediment.