Dead Fauna Research Articles

Comparison of alive and dead benthic foraminiferal fauna off the Changjiang Estuary: Understanding water-mass properties and taphonomic processes

Benthic foraminifera (BF) are utilized in palaeo-environmental reconstruction based on our understanding of how living individuals respond to environmental variations. However, there is still a lack of empirical insight into how non-environmental factors, such as taphonomic processes, influence the preservations of fossil BF in strata. In this study, we compare the spatial distribution and composition of alive and dead BF fauna in surface sediments to elucidate how well fossil foraminiferal fauna mirror quasi-contemporary alive BF groups indicative of different water masses off a mega-river (Changjiang) estuary, which is characterized by intense and complex river-sea interactions. On-site measurements of bottom water salinity, temperature, and dissolved oxygen were conducted in the summer to determine water mass properties. A same-site comparison of alive (Rose Bengal stained) and dead foraminiferal fauna in surface sediment samples over 73 stations was then carried out. Q-mode Hierarchical clustering analysis was used to differentiate foraminiferal assemblages based on the relative abundance of common species. Three distinct regions with different water-mass properties were identified. The distribution pattern of dead foraminiferal fauna is mainly inherited from alive fauna, while the density and diversity of the dead fauna were found to be higher than those of the alive one. Both alive and dead fauna were clustered into four assemblages. A few common alive species (small-agglutinated and thin-calcareous) were rarely found in dead fauna, and a few common dead species (preferring low temperature and indicating allochthonous sources) were rarely present in alive fauna. The alive foraminiferal abundance and diversity were mainly determined by food resources and environmental properties of salinity and temperature. Alive foraminiferal assemblages were separated by different water masses determined by river-sea interactions off the Changjiang Estuary. The “time-averaging” effect was found to be responsible for the higher density and diversity of the dead fauna. Disintegration of agglutinated tests, dissolution of calcareous tests and selective transportation were observed to contribute to the different species compositions between the alive and dead fauna. Nevertheless, indicative species-environment relations in alive and taphocoenose fauna were found to be almost homologous among most common species. This suggests that distinct benthic foraminiferal assemblages can be used to effectively differentiate between different water masses in the study coastal seas.

Intertidal foraminifera from the Mar Chiquita Coastal Lagoon, Buenos Aires Province, Argentina

The present study aims to analyze the composition and distribution of the intertidal foraminiferal assemblages of the Mar Chiquita Coastal Lagoon (southeast coast of Buenos Aires Province). For this purpose, the abundance and diversity of the living and dead fauna were determined; the taphonomic features of the tests were analyzed; and physico-chemical measurements were taken at 10 sites of the lagoon. The assemblages were constituted mainly by autochthonous fauna. The sediment grain size and salinity are the main variables that determine the distribution of species and discerned three assemblages, associated with three sub-environments. The first sub-environment of coarse sediment and mesohaline waters corresponds to non-vegetated plains in the mouth of the lagoon. It contains Buccella peruviana, Elphidium discoidale, and Quinqueloculina patagonica. The second sub-environment of fine sediment and mesohaline waters corresponds to non-vegetated plains in the inlet of the lagoon. It includes Elphidium gunteri, B. peruviana, Ammonia parkinsoniana, Ammonia tepida, Miliolinella subrotunda, Rosalina williamsoni, Pyrgo ringens, Discorbis peruvianus, and Q. patagonica. The third sub-environment of coarse sediment - waters ranging from polyhaline to mixoeuhaline and fine sediment - oligohaline waters corresponds to vegetated and non-vegetated plains and floodplains far from the mouth of the lagoon. It contains Ammonia spp, and E. gunteri.

First faunistic results on Valencia (Cresques) Seamount, with some ecological considerations

The living and dead fauna of Valencia Seamount, a deep promontory in the middle of the Balearic Basin which summit is at ca. 1100 m depth, is described by first time based in a rock dredge perfomed in a sedimentary area of the summit Mount. Surface-feeder polychaetes (the Paraonidae Levinsenia gracilis and Terebellidae as dominant), and taxodont bivalves (Ledella messanensis and Yoldiella ovulum) were the main species of benthos. We found alive remains of the bamboo coral Isidella elongata, a vulnerable, habitat-forming species in the deep Mediterranean. Benthos density was low (0.6 organisms/2 dm3 mud). Thanatocoenosis evidenced a rather moderate diversity of benthic bivalves (11 species) and gastropods (9 species) also dominated by surface deposit feeders. Fish (identified/quantified from sedimented otoliths) showed diversified and abundant mesopelagic fauna, mainly Myctophidae. More interestingly, we highlighted among benthopelagic fish the occurrence of recruits of Merluccius merluccius, Micromesistius poutassou, or Hymenocephalus italicus, all species that live in the neighboring slopes of the Iberian Peninsula and the Balearic Islands at quite shallower depths (at 100-700 m) than their distribution in the Valencia Seamount summit (1102–1130 m) based on the deposited otoliths found. Some ecological aspects were discussed and the necessity to consider the deep Valencia Seamount as a potential area that should be under protection.

Living and dead benthic foraminiferal distribution in two areas of the Ross Sea (Antarctica)

We investigated the living (stained) and dead benthic foraminiferal assemblages collected in surface sediment samples (0–1 cm) from two different areas (JOIDES Basin and Mawson Bank) of the Ross Sea (Antarctica). Samples were collected during the BEDROSE oceanographic cruise from January to February 2017. Four living and dead benthic foraminiferal fauna assemblages have been distinguished based on cluster analysis. The differences observed in the living and dead foraminiferal content from the two investigated areas are the result of taphonomic processes induced by the different oceanographic settings and environmental conditions. In the JOIDES Basin, agglutinated taxa Rhabdamminella cylindrica, Lagenammina difflugiformis, Adercotryma glomeratum, Recurvoides contortus, Reophax subfusiformis with high percentages of Trochammina group and Reophax spiculifer associated with the calcareous species Nonionella bradii and Astrononion echolsi characterize the living assemblages. The comparison between living and dead benthic foraminifera reveals considerable similarities in terms of the presence/absence of agglutinated species and differences in relative abundance of calcareous taxa. However, the major influencing factor in foraminiferal preservation appears to be the carbonate dissolution. Results from Mawson Bank show an almost exclusive presence of calcareous taxa with high percentages of Globocassidulina group in both living and dead assemblages. The dead fauna assemblage differs from the corresponding living assemblage by being more diverse documenting high-energy current influence on marine sedimentation. Graphic abstract

Impacts of hydrodynamics and pollutants on foraminiferal fauna distribution in the Santos Estuary (SE Brazil)

Superficial sediment samples of the Santos Estuary (SE Brazil) were analyzed for benthic foraminifera (dead fauna), aliphatic hydrocarbons (AHs), polycyclic aromatic hydrocarbons (PAHs), total organic carbon, total nitrogen, and trace metals. The foraminiferal fauna results were related to estuarine hydrodynamics and pollution parameters. The residual circulation of the estuary drives the transport of particles into the Santos channel. Thereby, tidal currents promote an advective transport of the species, including Pararotalia cananeiaensis, Discorbis sp. and Pseudononion japonicum from the Santos Bay to the upper estuary. Additionally, the dredging of the Santos channel leads to the suspension of sediments, favoring the post mortem transport. Enrichment factor and pollution load index for trace metals evidenced a contamination (mainly by Zn) in the Piacaguera River, and AHs and PAHs analyses revealed a widespread presence of petroleum-related residues and petroleum combustion products in the region of the upper estuary, with values of unresolved complex mixtures ranging from 95.2 to 402.3 µg g−1 and total PAHs concentrations from 1176 to 32,153.3 ng g−1. Although, the data obtained are from dead fauna, the impact of anthropogenic activities is also pointed by the benthic foraminifera, revealing that the pollutants impact are acting for some years in the upper estuary. The ecological indices show lowest values of richness and density, and low values of diversity for benthic foraminifera mainly in the upper estuary. Moreover, high values of dominance were observed due to the high abundance of the opportunistic species Ammonia sp1.

Influence of an Upper Bathyal Whale-fall on Benthic Foraminifera of Monterey Canyon, California (USA)

Aremotely operated vehicle was used to sample a graywhale carcass five days after it was deployed at a depth of 382 m in Monterey Canyon, California. Visual observations of the whale-fall (Whale-382p) documented that it was in the first stage of decomposition (the “necrophage†stage), with abundant hagfish and amphipods surrounding the carcass. A 21-cm, lithologically consistent fine-grained push core was taken under the carcass and analyzed for benthic foraminifera. No endemic foraminiferal species were found at this site. Pseudoparrella pacifica dominated both the living and dead assemblages. A general trend of decreasing foraminiferal abundance and species richness among the living and dead faunas was evident downcore, although several intervals below 5 cm contained a higher-than-expected abundance, species richness, and estuarine or shelfal benthic foraminifera, suggesting deposition of distal turbiditic deposits at the core site which is a common occurrence in Monterey Canyon.Because the percentage abundance of living and dead specimens of P. pacifica were similar in the upper 5 cm of the core (89% and 82%, respectively), the whale-fall does not appear to have influenced the benthic foraminiferal assemblage after five days on the seafloor.

History of the introduction of a species resembling the benthic foraminifera Nonionella stella in the Oslofjord (Norway): morphological, molecular and paleo-ecological evidences

Specimens resembling the benthic foraminifera Nonionella stella (Cushman and Moyer, 1930), a morphospecies originally described from the San Pedro Basin, California, USA, were observed for the first time in the Oslofjord (Norway) in 2012. This study investigates the Oslofjord Nonionella population in order to confirm its nonindigenous species (NIS) status and assess its introduction time. Morphological characterisation based on SEM imaging complemented by molecular identification using small subunit (SSU) rDNA sequencing and assessment of the recent past record (sediment core), were performed on material collected in the Oslofjord in 2016. Examination of the dead fauna showed that specimens resembling N. stella only appeared recently in the Oslofjord, confirming the NIS status of this population. Moreover, DNA results indicate that the Oslofjord specimens differ genetically from N. stella sampled in the Santa Barbara Basin (California USA). Hence, we propose to use the name Nonionella sp. T1 for the specimens sampled in the Oslofjord for the time being. In the southern part of the Skagerrak, specimens morphologically similar to Nonionella sp. T1 were reported as NIS in the Gullmar fjord (Sweden) in 2011 and in the Skagerrak in 2015. Molecular data indicate that the two populations from Gullmar- and Oslofjords are identical, based on their SSU rDNA sequences. In addition, analyses of foraminiferal dead assemblages suggest that the population from the Gullmar fjord settled prior to the Oslofjord population, i.e. ~ 1985 and about 2010, respectively. This implies that Nonionella sp. T1 may have been transported from Sweden to Norway by northward coastal currents.

Comparison of living and dead benthic foraminifera on the Portuguese margin: Understanding the taphonomical processes

Abstract Dead benthic foraminifera (> 150 μm) were studied in 23 sediment cores from the Portuguese Margin at water depths between 20 and 2000 m and located on 4 transects off the Douro, Mondego, Tagus and Sado river mouths and 1 transect in the Estremadura. For 10 stations, the dead faunal vertical distribution (0–8 cm) was first investigated in 4 different sediment horizons per core to evaluate the sampling effort necessary to have a representation of the dead fauna deposited under different environmental areas. As a result, it appears that the faunal vertical distribution is constant, except for the deepest environments where fragile taxa were identified in the top layers only. Dead foraminiferal assemblages in the 4–5 cm layer for all stations were then compared to previously published living foraminiferal assemblages (of March 2011) from the same cores to evaluate the taphonomical processes affecting major species. This improves the knowledge of the faunal distribution for a better benthic foraminiferal proxy for paleostudies. There was a considerable loss of some species in the dead fauna. Firstly, this concerns the fragile organic-cemented agglutinated taxa such as Reophax spp., Glomospira charoides, or Bathysiphon spp. Secondly, some calcitic species such as Nonion scaphum, Cancris auriculus, Ammonia beccarii or Bulimina aculeata that were particularly abundant in the living fauna on the inner shelf under the late winter high river discharge conditions, were also far less dominant in the dead fauna. Lastly, other species like Cassidulina carinata, Valvulineria bradyana, and Bulimina marginata systematically showed higher abundance in the dead fauna at the mid shelf. These species, related to eutrophic conditions occurring in summer during the upwelling activity, were therefore not well represented in the living fauna, collected in March. Transport of allochthonous specimens may also account for higher contribution in the dead community of some species like Cibicides lobatulus, Asterigerinata mamilla or Haynesina depressula, especially in coastal environments where hydrodynamic processes (river flood, winter storm, coastal drift) are more vigorous. Several species (U. mediterranea, U. bifurcata, T. agglutinans, H. balthica or B. costata), however, show little or no difference in both abundance and spatial occurrence between the living and dead faunas and provide a stable signal for paleoclimatic investigations.

Significance of replicates: Environmental and paleoenvironmental studies on benthic foraminifera and testate amoebae

Foraminifera (Rhizaria) and testate amoebae (Rhizaria and Amoebozoa) are single-celled organisms with marine and continental affinities. They are regarded as valuable bioindicators in transitional areas such as tidal and salt marshes and have been widely used for (paleo)-environmental characterization. Along-lasting debate regularly occurs on the use of living vs. dead fauna to accurately represent modern environments. Moreover, environmentally based benthic foraminiferal and testate amoebaean studies need a reliable sampling strategy to capture the spatial variability, particularly in transitional environments where patchiness complicates the data interpretations. The objective of the present study is therefore to define the minimum required number of replicates for capturing the variability of either living (environment) or dead (paleoenvironment) benthic foraminifera and testate amoebae. To address this question, 49 samples (i.e., replicates) were selected from a square meter zone in the tidal flat-salt marsh transitional zone along the Canche Estuary (Northern France). The range of faunal spatial variability was measured using geostatistical tools. The minimal number of samples for capturing the patchiness was determined using bootstrap resampling procedure. We provide evidence that for both living and dead fauna more than 26 samples (and even higher for some species) are needed to correctly evaluate the patchiness. Indeed, the living and dead fauna do not follow spatial homogenous trends, and this might bias paleoenvironmental interpretations. The commonly-suggested number of three replicates might not be enough to characterize the fauna in such heterogeneous environments.

Foraminíferos e Tecamebas Bentônicos do Estuário do Rio Godineau, Golfo de Paria, Ilha de Trinidad

In the Godineau River Estuary, located in Trinidad Island (off the northeast coast of Venezuela), were found 114 taxa of foraminifera and 17 of thecamoebians in the dead fauna. Most of the identified foraminiferal species were rare because they were transported from the Gulf of Paria to this estuary. The autochthonous foraminiferal assemblage was represented by several tropical estuarine species such as Ammonia tepida, Ammotium salsum, Arenoparrella mexicana, Cribroelphidium excavatum, Ammonia parkinsoniana, Haplophragmoides wilberti, Miliammina fusca and Ammotium cassis. The thecamoebians assemblages, found in the inner part of this estuary, were dominated by Cyclopyxis spp., Centropyxis spp., Difflugia corona and Difflugia urceolata. The relative abundance of the main species of foraminifera and thecamoebians were analyzed through Q-mode and R-mode cluster analyses. Statistical results revealed the presence of three different environments in the Godineau River Estuary related to different hydrodynamic conditions and more or less oceanic or fluvial influence. The first sector represents the most confined region of the estuary and was mainly composed by agglutinated foraminifera together with thecamoebians. The second sector was located in the middle part of the estuary and was associated with the presence of brackish waters. The third sector denotes the outermost part of the estuary characterized by the greatest hydrodynamic activity and highest oceanic influence within the estuary. This sector was marked by the occurrence of a large number typical-marine foraminifera species.

Foraminíferos e Tecamebas Bentônicos do Estuário do Rio Godineau, Golfo de Paria, Ilha de Trinidad

In the Godineau River Estuary, located in Trinidad Island (off the northeast coast of Venezuela), were found 114 taxa of foraminifera and 17 of thecamoebians in the dead fauna. Most of the identified foraminiferal species were rare because they were transported from the Gulf of Paria to this estuary. The autochthonous foraminiferal assemblage was represented by several tropical estuarine species such as Ammonia tepida, Ammotium salsum, Arenoparrella mexicana, Cribroelphidium excavatum, Ammonia parkinsoniana, Haplophragmoides wilberti, Miliammina fusca and Ammotium cassis. The thecamoebians assemblages, found in the inner part of this estuary, were dominated by Cyclopyxis spp., Centropyxis spp., Difflugia corona and Difflugia urceolata. The relative abundance of the main species of foraminifera and thecamoebians were analyzed through Q-mode and R-mode cluster analyses. Statistical results revealed the presence of three different environments in the Godineau River Estuary related to different hydrodynamic conditions and more or less oceanic or fluvial influence. The first sector represents the most confined region of the estuary and was mainly composed by agglutinated foraminifera together with thecamoebians. The second sector was located in the middle part of the estuary and was associated with the presence of brackish waters. The third sector denotes the outermost part of the estuary characterized by the greatest hydrodynamic activity and highest oceanic influence within the estuary. This sector was marked by the occurrence of a large number typical-marine foraminifera species.

Living and dead foraminiferal assemblages from an active submarine canyon and surrounding sectors: the Gioia Canyon system (Tyrrhenian Sea, Southern Italy)

Living (rose Bengal stained) and dead benthic foraminiferal assemblages were studied from 23 stations located between 60 and 670 m depth along the Gioia Canyon and the adjacent continental shelf and slope (Southern Tyrrhenian Sea). The aim of this study is to investigate the relationships among sedimentary processes, hydrological patterns and benthic foraminiferal distribution, in a highly dynamic environment. High sedimentation rates on the shelf and occasional turbidity flows along the canyon, lead to unstable environmental conditions at the seafloor that reflect on the microbenthic community influencing faunal density, diversity, species composition and distribution inside the sediment. The foraminiferal distribution seems to be controlled by sedimentary processes, nutrient supply and organic matter recycling, which in turn are strongly controlled by the seasonal variability of riverine inputs and current dynamics in the Gulf of Gioia.From the inner shelf to the upper continental slope (550 m depth), the living foraminiferal assemblage is dominated by agglutinated taxa, likely favored by the high terrigenous supply. Frequent eutrophic taxa (Valvulineria bradyana and Nonionella turgida) tolerant high turbidity (Leptohalysis scottii,) and low oxygen (Bolivina spp. and Bulimina spp.) are recorded on the edge of the inner shelf, where channeling, deposition of coastal deposits and occasional sediment gravity flows occur. In the outer sector of the shelf a turnover of species is observed; L. scottii replaced by the opportunistic species Reophax scorpiurus, and taxa indicative of high energy conditions (Cassidulina spp.) become dominant in association with mesotrophic species like Globocassidulina subglobosa. Along the continental slope, lower sedimentation rates and more stable environmental conditions support richer and more diversified foraminiferal assemblage. The abundance of Bulimina marginata indicates eutrophic conditions at the shallower station (300 m depth) whereas at greater depth (550 m) typical open slope species dominate (Gyroidina spp., Uvigerina mediterranea).Within the Gioia Canyon, benthic assemblage indicates environmental conditions similar to those observed in other Mediterranean and extra-Mediterranean canyons. The assemblage is characterized by eutrophic and low oxygen taxa (Bolivina spp., Bulimina spp.) in relation to periodical fluxes of sediment and organic matter.Similar relationships arise from the analysis of dead foraminiferal assemblages. However, the comparison between living and dead faunas highlight compositional and structural changes related to taphonomic processes.

Relationship between ‘live’ and dead benthic foraminiferal assemblages in the abyssal NE Atlantic

Dead foraminiferal assemblages within the sediment mixed layer provide an integrated, time-averaged view of the foraminiferal fauna, while the relationship between dead and live assemblages reflects the population dynamics of different species together with taphonomic processes operating over the last few hundred years. Here, we analysed four samples for ‘live’ (Rose-Bengal-stained) and dead benthic foraminifera (0–1cm sediment layer, >150µm) from four sites in the area of the Porcupine Abyssal Plain Sustained Observatory (PAP-SO; NE Atlantic, 4850m water depth). Two sites were located on abyssal hills and two on the adjacent abyssal plain. Our results indicate that the transition from live to dead benthic foraminiferal assemblages involved a dramatic loss of delicate agglutinated and organic-walled tests (e.g. Lagenammina, Nodellum, Reophax) with poor preservation potential, and to a lesser extent that of some relatively fragile calcareous tests (mostly miliolids), possibly a result of dissolution. Other processes, such as the transport of tests by bottom currents and predation, are unlikely to have substantially altered the composition of dead faunas. Positive live to dead ratios suggest that some species (notably Epistominella exigua and Bolivina spathulata) may have responded to recent phytodetritus input. Although the composition of live assemblages seemed to be influenced by seafloor topography (abyssal hills vs. plain), no such relation was found for dead assemblages. We suggest that PAP-SO fossil assemblages are likely to be comparable across topographically contrasting sites, and dominated by calcareous and some robust agglutinated forms with calcitic cement (e.g. Eggerella).

Benthic and Planktic Foraminifera as Indicators of Late Glacial to Holocene Paleoclimatic Changes in a Marginal Environment: An Example from the Southeastern Bay of Biscay.

Benthic and planktic foraminiferal assemblages from two sediment cores (2,000 m depth, 44 degrees 33'N, 2 degrees 45'W) were analyzed to first compare modern and dead faunas and next to study changes in the hydrology of the southeastern Bay of Biscay (SE BoB) over the last 12.8 cal ka BP. Considering benthic ecosystem characteristics, the first part of the paleorecord (12.8-7.6 cal ka BP) is composed of laminated sediments that may have resulted from turbiditic overflow events, whereas occurrences of transported species (e. g. Nonionella sp., Cassidulina carinata) attest of continental influence at the core location. After 7.6 cal ka BP, the sediment becomes bioturbated concomitantly to the stabilization of the sea-level. The benthic foraminiferal fauna is largely dominated by Uvigerina peregrina suggesting a high seasonality with seasonal pulsed organic matter fluxes to the seafloor. On the other hand, the planktic foraminiferal composition indicates that surface water masses were under the influence of the polar front in the early record, which retreated at about 11.5 cal ka BP. The early Holocene is characterized by relatively warm and stratified water masses at 8.4-4.8 cal ka BP. The last 4.8 cal ka BP records a gradual sea surface water cooling trend and enhanced foraminiferal production from similar to 2.6 cal ka BP until present. The early (12.8-10.5 cal ka BP) and late (2.3-1.7 cal ka BP) Holocene are characterized by the presence of the planktic species Globigerinoides ruber probably caused by intrusions of the Iberian Poleward Current (IPC), and a negative state of the North Atlantic Oscillation (NAO).

Recent benthic foraminifera in the Arctic Ocean and Kara Sea continental margin

Living (stained) and dead (unstained) benthic foraminifera from the Arctic Ocean and Kara Sea continental margin have been investigated to extend the knowledge on modern living and dead benthic foraminifera in the Arctic Ocean. Three living and three dead benthic foraminiferal fauna assemblages have been distinguished based on Q-mode cluster analysis. In the seasonally ice-free Nansen Basin, a living assemblage consisting of Ioanella tumidula–Stetsonia horvarthi assemblage has been established. On the permanently ice covered Lomonosov Ridge and Alpha Ridge in addition to the seasonally ice-free Nansen Basin, the living assemblage is characterized by I. tumidula–Oridorsalis tener–S. horvarthi assemblage. The seasonally ice-free and relatively shallow Kara Sea continental margin displays a living fauna assemblage with agglutinated Reophax species in addition to the calcareous species Cassidulina neoteretis, Epistominella nipponica, and Islandiella helenae. The dead assemblages from Alpha Ridge, Lomonosov Ridge and Nansen Basin with assemblages characterized by I. tumidula, O. tener and S. horvathi reflect the living assemblages well. The dead fauna assemblage from the Kara Sea continental margin differs from the corresponding living assemblage by showing less agglutinated specimens and dominance by C. neoteretis. However, there is also a relatively good potential reconstructing paleoenvironmental change from the Kara Sea continental margin, when it is taken into account that the agglutinated species are not well preserved in the dead assemblages.

Live–dead comparison of benthic foraminiferal faunas from the Rhône prodelta (Gulf of Lions, NW Mediterranean): Development of a proxy for palaeoenvironmental reconstructions

Dead benthic foraminiferal faunas (> 150 μm) from the Rhone prodelta (Gulf of Lions, NW Mediterranean) were analysed at 41 stations (15–100 m water depth) sampled in June 2005 and September 2006, and compared to the living faunas investigated during previous studies at the same stations. The comparison between dead and living assemblages enhances the understanding of taphonomic processes that may modify the composition of the dead faunas in this area. We observed a loss of individuals from living to dead assemblages of species characterised by a fairly fragile test and therefore more prone to fragmentation or dissolution (e.g., Bolivina alata, Quinqueloculina tenuicollis). Allochthonous dead and/or live specimens may be transported to some parts of the prodelta, particularly the shallowest sites where hydrodynamic processes (i.e., river flood, storm swells, longshore currents) are more intense. These specimens may originate from relict deltaic structures (e.g., Elphidium spp. from the lobe of Bras de Fer) or from surrounding areas (e.g., Ammonia beccarii forma beccarii from the river). Opportunistic species (e.g., Bulimina marginata, Cassidulina carinata) characterised by high reproductive rates have much higher relative abundances in the dead than in the living fauna. Cluster analyses based on dead foraminiferal assemblages divide our study area into four main thanatofacies directly related to distinct local environmental conditions prevailing in the prodelta. Close to the river mouth, Ammonia beccarii forma beccarii and Ammonia tepida are found in sediments subject to a high riverine influence (i.e., bottom currents, high organic and inorganic material input of continental origin). Elphidium species are abundant in the silty-sandy relict deltaic lobe west of the river mouth which is characterised by strong longshore currents that disturb the benthic environment. Nonion fabum, Rectuvigerina phlegeri and Valvulineria bradyana are found along the coast west of the Rhone River mouth, in the area defined as the “river plume” thanatofacies. In the more stable and deeper prodeltaic area, species known to feed on fresh phytodetritus (e.g., Bulimina aculeata/marginata, C. carinata, Hyalinea balthica) dominate the faunas. Since only minor variations in species relative abundances and spatial distributional patterns are observed between the living and the dead faunas, we consider that our thanatofacies have not been influenced by substantial transport of dead tests. This suggests that fossil benthic foraminifera can provide a reliable tool for investigating the development of the palaeo-Rhone prodelta.

Benthic foraminifera from the deep-water Niger delta (Gulf of Guinea): Assessing present-day and past activity of hydrate pockmarks

We present ecological and isotopic (δ18O and δ13C) data on benthic foraminifera sampled from 4 deep-sea stations in a pockmark field from the deep-water Niger delta (Gulf of Guinea, Equatorial Atlantic Ocean). In addition, a series of sedimentological and (bio)geochemical data are shown to back up foraminiferal observations. All stations are located within 1.2km of each other, so prevailing oceanographic conditions can be assumed to be similar at each site. Two of the sites (GMMC-01 and GMMC-02) are located in a pockmark (named “pockmark A”) where current methane seepages were recorded by ROV observations. A third station (GMMC-03) is located in the topographic depression interpreted as a collapsed pockmark (named “pockmark B”). The fourth site (GMMC-04) is a reference station, without evidence of past or present seepages. Our observations show that degraded organic matter with low bio-availability is present at all stations with a preferential burial of organic compounds in topographic depressions (GMMC-03 station). Authigenic aragonite is abundant in surface sediments at stations GMMC-01 and -02. Its precipitation is likely related to high rates of methane oxidation during past seep events in episodically active pockmark A. In contrast, the absence of anaerobic methanotrophic Archaea (ANME) during the sampling period (November 2011) suggests that only moderate sulphide and methane oxidation take place close to the sediment–water interface. Compared to the reference site GMMC-04, living foraminifera at the collapsed and episodically active pockmarks show minor changes in terms of diversity, standing stocks and faunal composition. However, the δ13C signal of living and dead (but well-preserved) foraminiferal species (Ceratobulimina contraria, Melonis barleeanus, Uvigerina peregrina) is depleted in the episodically active pockmark A compared to the other stations. Overgrowth of authigenic carbonate on altered foraminifera generates an important shift to lower δ13C values. Dead faunas carry a complex time-averaged message, integrating taphonomic gains and losses related to the temporal variability of gas emission. They reveal major faunal differences that may be useful to detect gas hydrate seepages in different pockmark stages.

"MONOSPECIFIC" AND NEAR-MONOSPECIFIC BENTHIC FORAMINIFERAL FAUNAS, NEW ZEALAND

Research Article| July 01, 2014 “MONOSPECIFIC” AND NEAR-MONOSPECIFIC BENTHIC FORAMINIFERAL FAUNAS, NEW ZEALAND Bruce W. Hayward Bruce W. Hayward Geomarine Research, 49 Swainston Rd, St Johns, Auckland, New Zealand, e-mail: b.hayward@geomarine.org.nz Search for other works by this author on: GSW Google Scholar Journal of Foraminiferal Research (2014) 44 (3): 300–315. https://doi.org/10.2113/gsjfr.44.3.300 Article history received: 15 Jul 2013 accepted: 23 Mar 2014 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Bruce W. Hayward; “MONOSPECIFIC” AND NEAR-MONOSPECIFIC BENTHIC FORAMINIFERAL FAUNAS, NEW ZEALAND. Journal of Foraminiferal Research 2014;; 44 (3): 300–315. doi: https://doi.org/10.2113/gsjfr.44.3.300 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract Thirteen benthic foraminiferal species dominate modern “monospecific” faunas (dead faunas with >80% of one species in >63-μm samples) in New Zealand. These faunas occur in sheltered, often brackish, intertidal or shallow-subtidal environments, never deeper than 25 m. None occurs along exposed coasts or in the open ocean. Seven agglutinated species (Entzia macrescens, Haplophragmoides wilberti, H. manilaensis, Miliammina fusca, M. obliqua, Trochammina inflata, Trochamminita salsa) dominate “monospecific” faunas in salt marshes with varying salinity and elevational ranges. All but H. manilaensis have been recorded comprising 99–100% of at least one fauna. A further six species (Ammobaculites exiguus, Ammonia aoteana, Ammotium fragile, Elphidium excavatum clavatum, E. williamsoni, E. gunteri) dominate “monospecific” faunas in unvegetated intertidal and shallow-subtidal (<3 m), sheltered estuary, inlet, or lagoon settings. “Monospecific” Amb. exiguus faunas are inferred to have been produced by dissolution of calcareous components. A further 17 species dominate modern near-monospecific faunas (50–80% of one species), 11 at depths <50 m and six in the open ocean at 50–4000-m depth. “Monospecific” and near-monospecific faunas are more common in higher latitudes, where overall species diversity is lower.Six species dominate “monospecific” early Miocene faunas in northern New Zealand: Elphidium crispum in a sheltered gravel beach; Nonionella novozealandica in a deep-water (50–100 m), possibly dysoxic harbour; and three larger, more robust species (Amphistegina aucklandica, Lepidocyclina orakiensis, Miogypsina intermedia) in current- or wave-concentrated beach or shallow-marine deposits. The only bathyal or abyssal “monospecific” fauna is dominated by Amphimorphinella butonensis occurring in a fossil hydrocarbon seep setting.Many of the modern “monospecific” faunas (especially those in salt marshes) are cosmopolitan, whilst most of the fossil and some of the modern faunas are endemic to the New Zealand region. These high-dominance faunas are produced by taphonomic and ecological processes. Taphonomic causes include wave or current concentration by winnowing or transport in high energy, shallow-marine environments and carbonate dissolution in low pH, brackish, salt marsh or deep-sea settings. Ecological drivers include highly specific adaptations that allow species to outcompete all others in stressful (intertidal), strongly variable (high-tidal brackish), or unusual (hydrocarbon seep) environments. Sometimes high test productivity of opportunistic species may result in near-monospecific faunas. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

DISTRIBUTION OF FORAMINIFERA IN A SUBTROPICAL BRAZILIAN ESTUARINE SYSTEM

The Santos Estuary, an estuarine system bordering the cities of Santos, Sao Vicente, and Cubatao in southeastern Brazil, contains the country’s largest harbor and main industrial center that have been impacted by industrial and domestic effluents since the late 19 th century. We report here on the distribution of benthic foraminifera and related environmental parameters in this estuary system during the summer and winter of 2007. The foraminiferal fauna is representative of mixohaline environments, and includes 107 live + dead taxa, of which 73 are calcareous benthic, 33 agglutinated, and one planktonic. Most of the calcareous specimens belong to the genera Ammonia, Elphidium , and Quinqueloculina and the species Nonionella atlantica . The living population was ~10% of the total foraminiferal fauna, and the dominant living species were similar to those in the total live + dead fauna. Ammonia beccarii was dominant in most of the stations during summer and winter. It could be considered opportunistic due to its high abundance in samples with low diversity and richness. It is not evident if the effects of human population density on the study area impacted the distribution of the foraminiferal fauna, because low proportions of deformed tests and low values of abundance, richness, and diversity were also found in pristine areas near Santos, Sao Vicente, and Cubatao.

Benthic foraminiferal thanatocoenoses from the Cap-Ferret Canyon area (NE Atlantic): A complex interplay between hydro-sedimentary and biological processes

Benthic foraminiferal thanatocoenoses from the Cap-Ferret Canyon area were studied in the >150-µm fraction of 4–5cm deep sediment levels, at 13 stations. The shallowest station (151m depth) is located at the shelf break, close to the canyon head. All other stations are located along two bathymetric transects: seven stations along the canyon axis between 300 and 3000m depth, and five stations from 300m to 2000m depth along the southern flank of the canyon. The comparison between the live (Rose-Bengal-stained) and dead assemblages shows that biological (i.e. population dynamic) and taphonomic processes (i.e. test destruction, transport) generate important discrepancies between live and dead assemblages. An important question is, to what degree post-mortem transport and redeposition of foraminiferal tests contribute to the difference between living and dead assemblages? The composition of the thanatocoenoses (<1% of neritic species) indicates that there is no substantial transport of shells >150µm from the inner continental shelf to the Cap-Ferret Canyon axis. However, transport of tests from outer shelf or upper canyon axis towards deeper sites occurs, as indicated by an increase of diversity indices of the dead fauna along the canyon axis. Moreover, some species (e.g., Cassidulina carinata) are observed in the living fauna restricted to the shallow sites, but occur in important amounts in the dead fauna at deeper stations, suggesting that these taxa have been transported from upper canyon stations toward deeper sites. Since Cap-Ferret Canyon is inactive in terms of massive sediment transport (i.e. gravity events), downslope transport of foraminiferal tests probably takes place in nepheloid layers. Downslope transports of foraminiferal tests may create important biases for the utilisation of paleoceanographic proxies using the assemblage characteristics and/or the geochemical composition of selected species. However, the study of dead assemblages along a canyon axis can give important clues about the sedimentary dynamics, especially an idea of the quantity of reworked foraminifera transported through the canyon axis. Along the adjacent flank, such evidence of downslope transport was not observed. Despite taphonomic (test destruction) and biological processes (population dynamics), the live fauna closely resembles the distribution and the composition of the dead assemblage. Therefore, ecological information obtained from the fossil flank samples can be more reliably used to reconstruct paleoenvironmental conditions.