Foraminiferal Community Structure Research Articles

Using foraminifera to assess changes in marine coastal habitats of Caribbean Panama since the Middle Holocene

Humans settled the Bocas del Toro archipelago of Caribbean Panama ~690 CE. Coastal land was cleared for agriculture in the late 1880s and in recent decades water quality degradation has been detected. To investigate changes that support a decline in water quality and to assess differences in salinity caused by increased runoff from cleared lands, benthic foraminifera of Almirante Bay served as an environmental proxy to compare modern and Middle Holocene times. The foraminiferal community structure of 17 modern mangrove, seagrass, and coral reef habitats <2 m deep was analyzed in combination with 18 samples of ~6600-year-old coral reef, seagrass and muddy molluscan biofacies from Isla Colón island.The foraminiferal communities' species and diversity overlap considerably among habitats of both ages, and there is more difference in species' proportions between the ages than among habitats of either age. These patterns reflect high connectivity across adjacent habitats in this embayed, patch-reef setting. Assemblages from Middle Holocene molluscan muds and modern mangroves are least diverse, fairly similar, and well differentiated from those of seagrass and coral habitats. Foraminiferal wall structure suggests more freshwater input in modern times, consistent with forest clear-cutting for agriculture, although both ages fall within the low end of normal salinity. Increased freshwater input influenced assemblage changes but they were not sufficient to reduce measured diversity. Reported declines in the bay's water quality have also not resulted in net foraminiferal diversity loss from ~6600 years ago, indicating substantial resilience in these extremely shallow, tropical coastal communities.

Benthic foraminiferal community structure and its response to environmental factors revealed using high-throughput sequencing in the Zhoushan Fishing Ground, East China Sea

Benthic foraminifera are excellent tools for monitoring marine environments and reconstructing paleoenvironments. This study investigated the structure and diversity of benthic foraminiferal communities in 20 superficial sediment samples obtained from the Zhoushan Fishing Ground (ZFG) using high-throughput sequencing based on small subunit ribosomal DNA and RNA amplification. The results revealed Rotaliida as the most dominant group, with spatial heterogeneity in foraminiferal distribution. Total benthic foraminiferal communities exhibited higher species richness and diversity compared to active communities. While heavy metal pollution in the ZFG was moderate, areas with elevated concentrations of heavy metals exhibited low diversity and richness in foraminiferal communities. Total foraminiferal community structure was primarily influenced by factors such as water depth and Hg, Pb, Cd, and Zn levels. Notably, Hg levels emerged as a critical factor impacting the structure and diversity of the active foraminiferal community. The dominant species, Operculina, exhibited tolerance toward heavy metal pollution.

Holocene paleo-redox conditions in a microbial dolomitic lake using benthic foraminifera as bioindicators

Brejo do Espinho coastal lake (LBE) is one of the few places in the world where dolomite [CaMg(CO3)2] is precipitating in the modern environment under microbially induced processes and low oxygen conditions. We use pore morphometry of the foraminifera Ammonia cf. A. veneta to evaluate paleo-O2 dynamics during the dolomitic depositional phase that took place at LBE in the late Holocene. Foraminiferal community structure was also investigated, and results were compared to bulk isotopic composition of carbonates, total organic carbon (TOC), and X-ray Diffraction of sediments (XRD). The correlation matrix (Spearman method) showed that Ammonia test pores morphometric parameters displayed significant correlations with overall biotic and geochemical data, with pore area presenting a relatively higher association. Ammonia test pores were primarily controlled by the degradation of organic matter (Pore area-TOC, r = −0.84), and foraminifera density appeared to be influenced by oxygen changes, with a higher abundance in the highest porosity intervals (Pore area-N, r = 0.82), indicating a direct effect of oxygen penetration on species dominance. These data also reveal a tolerant behavior of the low-O2 bioindicator species Quinqueloculina laevigata and A. veneta. Understanding microbe-mineral interactions is critical for interpreting paleo records, and our data provide strong support for coupling assemblage and pores analysis as paleo-O2 bioindicators for paleo-redox coastal settings.

Assessing the effect of Amphistegina lobifera invasion on infralittoral benthic foraminiferal assemblages in the Sicily Channel (Central Mediterranean)

This article documents, through a quantitative approach, the negative effect of the highly invasive species Amphistegina lobifera Larsen, 1976 on native benthic foraminiferal assemblages of coastal areas in the Sicily Channel (Central Mediterranean). A nested sampling design was applied through the comparison of benthic foraminiferal community structure across three areas that are known to be at different stages of invasion (i.e. Maltese Islands - advanced, southern Sicily – medium, and eastern Sicily - early). Results suggested that both diversity and richness of benthic foraminiferal community from the Maltese Islands were strongly modified by increased abundances of A. lobifera. In contrast, this phenomenon is less evident in southern and eastern Sicily, where the invader displayed lower abundances and the community structure was more diversified. Collected data also allowed for predicting what could happen in the near future in the whole Sicily Channel, as well as in the rest of the Mediterranean Sea.

Decadal trend of plankton community change and habitat shoaling in the Arctic gateway recorded by planktonic foraminifera.

The Fram Strait plays a crucial role in regulating the heat and sea-ice dynamics in the Arctic. In response to the ongoing global warming, the marine biota of this Arctic gateway is experiencing significant changes with increasing advection of Atlantic species. The footprint of this 'Atlantification' has been identified in isolated observations across the plankton community, but a systematic, multi-decadal perspective on how regional climate change facilitates the invasion of Atlantic species and affects the ecology of the resident species is lacking. Here we evaluate a series of 51 depth-resolved plankton profiles collected in the Fram Strait during seven surveys between 1985 and 2015, using planktonic foraminifera as a proxy for changes in both the pelagic community composition and species vertical habitat depth. The time series reveals a progressive shift towards more Atlantic species, occurring independently of changes in local environmental conditions. We conclude that this trend is reflecting higher production of the Atlantic species in the Nordic Seas, from where they are advected into the Fram Strait. At the same time, we observe the ongoing extensive sea-ice export from the Arctic and associated cooling-induced decline in density and habitat shoaling of the subpolar Turborotalita quinqueloba, whereas the resident Neogloboquadrina pachyderma persists. As a result, the planktonic foraminiferal community and vertical structure in the Fram Strait shift to a new state, driven by both remote forcing of the Atlantic invaders and local climatic changes acting on the resident species. The strong summer export of Arctic sea ice has so far buffered larger plankton transformation. We predict that if the sea-ice export will decrease, the Arctic gateway will experience rapid restructuring of the pelagic community, even in the absence of further warming. Such a large change in the gateway region will likely propagate into the Arctic proper.

Spatial distribution of benthic foraminifera in the Lagos Lagoon (Nigeria): Tracing the impact of environmental perturbations.

Lagos Lagoon is among Africa’s largest estuarine ecosystems, bordered by one of the fastest growing megacities in the world and the ultimate repository of contaminants carried in industrial, municipal and agricultural wastes. The high levels of pollutants have progressively deteriorated the water quality, adversely affected lagoon ecosystems, impacted the livelihood of the coastal population and pose serious risks to human health. Benthic foraminifera are excellent proxies and sensitive bioindicators of environmental disturbances but comprehensive studies on the structure, distribution, diversity and impact of pollution upon foraminiferal communities have not yet been conducted in the Lagos Lagoon. To demonstrate the potential of foraminifera as proxies of environmental perturbations, benthic foraminifera were investigated on a lagoon-wide basis. Lagos Lagoon comprises areas that range from low levels of direct impact to those of severely affected by various forms of anthropogenic disturbance. The goals of this study are to analyze patterns of distribution and species richness, to document foraminiferal community structures, and to identify taxa that track documented records of pollution in Lagos Lagoon sediments. Heat maps were generated from abundance records for selected species to illustrate environmental preferences and relative resistance levels to individual forms of anthropogenic disturbance. Sediments were analyzed for a range of physicochemical properties, via a multi-parameter sensor probe-device, including temperature, pH, depth and total dissolved solids (TDS). Quantitative analysis of 24 sediment samples yielded a total 3872 individuals of benthic foraminifera that belong to 42 species and 25 genera. They comprise 10 porcellaneous, 22 hyaline perforate and 10 agglutinated species. Ammobaculites exiguus, Ammotium salsum, Ammonia aoteana, Ammonia convexa and Trochammina sp. 1 have been found to be the most abundant species. For the first time, the complete present-day foraminifera fauna is illustrated here via scanning electron microscopy. The features recorded allow to assess the spatial effects of pollution upon foraminiferal assemblages on a lagoon-wide basis. The data generated may ultimately form the basis to assess the progressive deterioration of Lagos Lagoon ecosystems from cores by using benthic foraminifera as bioindicators of environmental perturbation.

Invasion of amphisteginid foraminifera in the Adriatic Sea

Amphisteginid foraminifera are larger symbiont-bearing foraminifera that are abundant in tropical and subtropical reef and shelf regions of the world’s oceans. There is now unequivocal evidence that climate change has led to an expansion of tropical belts. As temperatures rise, surface isotherms are shifting poleward and habitat ranges are moving towards higher latitudes. Fueled by substantial warming, the Mediterranean has been identified as one of the most severely affected areas. This study documents for the first time that amphisteginid foraminifera have now crossed the Strait of Otranto and invaded the eastern Adriatic coast along southern Albania. Sampling on the opposite side along the southern part of the Italian boot shows, however, that amphisteginid foraminifera have not yet colonized the western coast of the Adriatic. The asymmetric invasion of the Adriatic displays spatial heterogeneity, where the progressive colonization follows the major surface currents with a northerly flow along the eastern coast and a southerly return along the western coastline. Previous sampling along Ionian Sea sample sites provides a baseline chronology allowing computations of range expansion rates. The observed recent rate of range expansion in Amphistegina is computed between 4.0 and 10 km/year−1 and provides strong support for current species model projections. Based on the new data, the range boundary shift is projected to lead to a total northward range expansion of 5.2° latitude in the year 2100. The latitudinal range extension computed for the Mediterranean is thus almost twice as large as those computed for the southern hemisphere. The ongoing range extension into new areas of the Mediterranean Sea is shown to trigger changes in community structures with potential consequences for ecosystem functioning. Numerical abundances and impacts of invasive amphisteginids are greatest at shallow depths <20 m. Evidence is now accumulating that the invasion of amphisteginid foraminifera results in (1) a loss of benthic foraminiferal biodiversity, (2) alterations of foraminiferal community structures and (3) shifts in abundances of functional groups of foraminifera.

Holocene benthic foraminiferal assemblages indicate long-term marginality of reef habitats from Moreton Bay, Australia

Since European settlement (ca. 1824CE), the subtropical inshore reefs of Moreton Bay have undergone rapid deterioration in water quality from changes in land-use practices, resource exploitation and rapid population growth, spurring marine managers to assess the drivers of ecological shifts. However, the short temporal-scale of most studies is an inadequate baseline for understanding the severity and magnitude of biological response. We present millennial-scale records employing palaeoecological and quantitative multivariate techniques within a concise chronological framework to analyse benthic foraminiferal community structure of reefs in Moreton Bay, Queensland. Well-constrained, U/Th-dated, millennial-scale records from sediment cores were used to document the long-term response of foraminifers to natural environmental variability. The temporal and spatial distribution patterns of foraminifers reveal long-term marginality throughout the ~7400years of Holocene history, prior to European settlement. While specific faunal response to the effects of relative ENSO-climate and sea level fall are difficult to disentangle, the earlier phases of reef development are already represented by marginal taxa indicating possibly an earlier response to a decline in conditions. Overall, long-term consistency in conditions favoured two types of low diversity reef assemblages: 1) high density of small, heterotrophic and opportunistic species and 2) low density of photosymbiotic foraminiferal assemblages. Comparison of foraminiferal community composition between the Holocene and the present day indicates overlap in species composition supporting long-term marginality, particularly in the Western Bay. Such combined palaeoecological and recent studies can benefit long-term initiatives for monitoring present and future water quality conditions in the Bay's reef habitats.

ALPHA AND BETA DIVERSITY OF FORAMINIFERA THAT ENCRUST THE ANTARCTIC SCALLOP ADAMUSSIUM COLBECKI: ECOLOGICAL CONNECTIVITY AMONG SHELLS AND BETWEEN SITES

Benthic foraminifera are ubiquitous marine organisms in Antarctica, but little is known about their ecology despite their importance as climate-change proxies. A fundamental question remains unanswered: is foraminiferal diversity highly localized and similar to reports for Antarctic benthic invertebrates? If so, high endemism would result driven by dispersal limitation with little connectivity among sites. To answer this question, the composition, abundance, spatial distribution and alpha (α) and beta (β) diversity of foraminiferal species that encrust living shells of the Antarctic scallop Adamussium colbecki were compared within and between two sites located 30-km apart in McMurdo Sound, Ross Sea, Antarctica: Bay of Sails (BOS), an open coastal region with annual sea-ice cover, and Explorers Cove (EC), a protected embayment with multiannual sea-ice cover. Foraminiferal community structure differed between the sites, generated by variations in species abundance, turnover of rare species, and heterogeneity in species composition between top and bottom valves. Foraminifera were significantly more common on the scallop’s auricles, perhaps driven by nutrients generated by the scallop. Calcareous taxa were significantly more abundant at EC despite lower seawater pH, while agglutinated taxa were significantly more abundant at BOS. Alpha diversity (species richness, Shannon H , e H ) was higher at BOS than at EC and is similar to deep-sea diversity reported for Caribbean encrusting foraminifera. Based on Shannon H , foraminifera at EC may represent a stressed community dominated by Cibicides antarcticus , while those at BOS may represent a transitional community. Within-site β-diversity was high, spurred by the turnover of rare species between top and bottom valves, which acted as separate microhabitats. Higher β-diversity at BOS suggests that foraminiferal dispersal and recruitment were more localized than at EC. Additive partitioning revealed that encrusting diversity was mostly held at the local level, and that BOS and EC have high connectivity, similar to deep-sea communities. The Antarctic endemicity of these protists is questionable, and is in stark contrast to Antarctic invertebrates with high within- and between-site diversity. Therefore, Antarctic encrusting foraminifera appear to be influenced primarily by niche-based processes, rather than dispersal limitation. Indeed, habitat islands, such as carbonate shells, are essential for generating Antarctic diversity, and are integral for the conservation of Antarctica’s unique polar ecosystem.

Millennium-scale records of benthic foraminiferal communities from the central Great Barrier Reef reveal spatial differences and temporal consistency

Understanding long-term community dynamics and the ways in which they respond to major disturbances is a central management theme within coastal marine ecosystems. River outputs from the Queensland coastline directly affect inshore marine communities of the Great Barrier Reef (GBR), Australia. Of these, the Burdekin River exports the highest volume of terrestrial runoff. Following European settlement in the mid-19th century, over three quarters of the native vegetation from the Burdekin catchment were cleared for agricultural purposes. Despite such extensive historical catchment modification, the impact of these changes on the inshore GBR is largely unknown, primarily due to the paucity of long-term ecological data. To assess the effects of modern land-use change on inshore reef environments and to establish an historical baseline of community structure, we examined the sedimentary geochemistry and benthic foraminiferal assemblages of eight sediment cores collected from two coral reefs situated inside (Pandora) and outside (Havannah) an inner-shelf sediment prism formed during the Holocene. Foraminiferal community structure was reconstructed from the past millennium, and the time series was constrained using U-series dating of coral fragments within the cores. Environmental records were reconstructed using stable carbon isotopes (δ13C) and elemental C:N ratios from bulk sediment samples. Non-parametric analysis of community structure in benthic foraminifers indicated no change in community structure through time at either reef. Despite this apparent ecological persistence through time, significant differences in foraminiferal community structure were observed between the two reefs. The communities were clearly characterized by different functional groups; heterotrophic genera were persistent within, and symbiont-bearing genera were persistent outside, the Holocene inshore sediment wedge. We found no difference in the source of organic matter (interpreted from δ13C values) either between reefs or through time, yet elemental C:N ratios indicated a difference in the amount of organic matter between reefs. The influence of the Holocene inshore sediment wedge was demonstrated by the dissimilarity in sedimentary C:N ratios between the two reefs.

BENTHIC FORAMINIFERAL DISTRIBUTION IN SURFACE SEDIMENTS OF ZHUJIANG ESTUARY AND ITS ENVIRONMENTAL IMPLICATIONS

134 grab surface sediments were collected from the Zhujiang River estuary with the support of projects 908-01-CJ14 and 908-01-CJ15.In the sediment samples discovered are 106 benthic foraminiferal species belonging to 68 genera and 3 suborders,including 65 Hyaline,21 porcellaneous and 20 agglutinated species.Benthic foraminiferal species at different locations of the Zhujiang River estuary is examined for abundance,number of species and compound diversity H(S).Foraminiferal abundance,number of species and diversity increased rapidly from the estuary to shallow sea.Foraminiferal abundance changes from several to tens of thousands;number of species changes from 1 to 48 and diversity does from 1 to 3.Factor analysis and Pearson correlation matrix was performed on foraminiferal census data of species content higher than 2% which are present in at least three samples.3 factors were obtained accounting for 87.2% of the total variance.Two benthic foraminiferal subgroups and one group,Ammonia beccarii-Elphidium nakanokawaense subgroup、Ammonia beccarii-Haplophragmoides canariensis subgroup and Hanzawaia nipponica-Elphidium advenum-Ammonia compressiuscula group,were classified according to factor score of foraminiferal genus.Further,there is some kind of relationship between the foraminaferal distribution and environment.Water depth and salinity control foraminiferal distribution and community structure,and sediment type,water dynamics and sedimentary rate affect its ecological structure as well.

Living deep-sea benthic foraminifera from the Cap de Creus Canyon (western Mediterranean): Faunal–geochemical interactions

Rose-Bengal-stained benthic foraminifera were sampled along a depth transect from the Cap de Creus Canyon and the adjacent slope. Well-stained individuals were studied in the top 5cm of sediment and the faunal abundances and assemblages were compared against pore-water geochemistry and biochemical composition of the sediment. Total standing stocks (TSS) of foraminifera were positively correlated with the chloroplastic pigment equivalents inventory (CPEinv; here interpreted as food quantity) and the ratio of chlorophyll-a and phaeopigment inventories (Chl-ainv/Phaeoinv; here interpreted as food quality), suggesting food quality as well as quantity play an important role in structuring the foraminiferal community. Food quality and food quantity were also identified by detrended correspondence analyses (DCA) as being the most important environmental parameters shaping the foraminiferal community structure (abundance and faunal composition). In addition, sediment redox chemistry (based here on pore-water nitrate) played an important role in controlling the foraminiferal diversity (H′) as a negative correlation was seen between this parameter and pore-water nitrate penetration depth (NPD). No conclusive evidence of intense physical disturbance on the benthic canyon community was observed, although it could be anticipated in the area due to shelf-water downwelling (SWD) and dense shelf-water cascading (DSWC). However, foraminiferal faunas living in the canyon head and upper canyon environments may profit from the higher organic-matter availability, which is likely to be related to SWD and DSWC. The similarity between the deeper canyon and slope faunas suggests that sediment characteristics and the associated organic-matter transported by SWC and DSWC do not have a permanent effect at these depths.

Response of Early Eocene deep-water benthic foraminifera to volcanic ash falls in the Polish Outer Carpathians: Palaeocological implications

Lower Eocene sediments of the Subsilesian Unit of the Polish Carpathians contain bentonite layers that were deposited in a deep-water basinal environment. Foraminiferal assemblages occurring within the bentonites and in the surrounding shales show important differences in taxonomical composition, the proportions of ecological groups, and test composition. Foraminiferal assemblages collected from bentonites are impoverished, display smaller test size, are dominated by a single opportunistic taxon, and have lower numbers of suspension feeders in comparison with assemblages surrounding sediments. In addition, bentonite assemblages show a test composition comprised of white fine-grained quartz, and include a greater number of juvenile forms with test abnormalities. The extent of such discrepancies is variable and depends on the thickness of the bentonite layers. The deposition of volcanic ash layers (bentonites) represented catastrophic events for benthic foraminifera. After each ash fall event a kill layer was formed, and settled by an opportunistic foraminiferal group dominated by specimens of the epifaunal Glomospira charoides, leading to the formation of nearly monospecific foraminiferal assemblages. In the case of thin ash layers some infaunal species are found. These organisms probably survived the deposition of volcanic ash and associated unfavourable conditions beneath the surficial sediment layer. The studied sections of the Subsilesian Unit include intervals containing several bentonite layers, indicating that the deposition of volcanic ash was a recurrent phenomenon. Following the deposition of volcanic ash, a relatively quick recovery of the foraminiferal community structure took place, and changes in the foraminiferal community proceeded each time according to the same sequence.

THE DISTRIBUTION OF BENTHIC FORAMINIFERA IN DAMAR ISLAND AND JUKUNG ISLAND, SERIBU ISLANDS

Seribu Islands are archipelago within Jakarta Bay built upon the pleistocene coral formation of the Sunda Shelf. The islands are characterized by unique and high biodiversity such as coral reefs. Since coral reef degradation would lead to a decrease of human prosperity, the determination of the coral reef quality is of high importance. Foraminifera offers an early warning system for the coral reef condition, as exemplified by the FORAM Index, i.e. Foraminifera in Reef Assessment and Monitoring Index. This study compared the foraminiferal community structure and the FORAM Index of two islands between the Damar Besar and Jukung. Both islands were dominated by symbiont-bearing foraminifera of the genera Amphistegina, Calcarina, Heterostegina, Marginophora, and Operculina. However, the number of benthic foraminifers at Jukung Island was higher than that at Damar Besar Island, having 17 individuals per species on average. Jukung Island was a conducive site to reef growth, as indicated by a FORAM Index (between 6,48 and 6,57), and Damar Besar Island was liable to environmental change.

THE DISTRIBUTION OF BENTHIC FORAMINIFERA IN DAMAR ISLAND AND JUKUNG ISLAND, SERIBU ISLANDS

Seribu Islands are archipelago within Jakarta Bay built upon the pleistocene coral formation of the Sunda Shelf. The islands are characterized by unique and high biodiversity such as coral reefs. Since coral reef degradation would lead to a decrease of human prosperity, the determination of the coral reef quality is of high importance. Foraminifera offers an early warning system for the coral reef condition, as exemplified by the FORAM Index, i.e. Foraminifera in Reef Assessment and Monitoring Index. This study compared the foraminiferal community structure and the FORAM Index of two islands between the Damar Besar and Jukung. Both islands were dominated by symbiont-bearing foraminifera of the genera Amphistegina, Calcarina, Heterostegina, Marginophora, and Operculina. However, the number of benthic foraminifers at Jukung Island was higher than that at Damar Besar Island, having 17 individuals per species on average. Jukung Island was a conducive site to reef growth, as indicated by a FORAM Index (between 6,48 and 6,57), and Damar Besar Island was liable to environmental change.

RETARDED RESPONSE BY MACROFAUNA-SIZE FORAMINIFERA TO PHYTODETRITUS IN A DEEP NORWEGIAN FJORD

Due to the scarcity of information concerning the role that large foraminifera play in deep-sea carbon cycling, the response of a foraminiferal community (>250 pm) to a simulated phytodetritus sedimentation event was assessed over two weeks using sediment cores collected from a deep-fjord environment. Sediment cores were collected from similar to 700 in water depth in the Korsfjorden, western Norway, and incubated ex situ with 1 9 C-org m(2) of labile C-13-labeled Skeletonema costatum for 2, 7, and 14 days. We selectively picked (without prior staining) cytoplasm-containing foraminifera and found the foraminiferal community to be largely dominated (91%) by the deep-dwelling species Globobulimina turgida and Melonis barleeanum, as well as the shallow infaunal species 1 Hyalinea balthica. None of the >250 mu m, cytoplasm-containing fraction was involved in carbon uptake during the first 7 days. After 14 days, 3% of the foraminiferal samples possessed delta C-13 signatures indicative of carbon uptake, but the uptake was confined to the surface-living (0-2 cm) G. turgida. Foraminifera contributed 2.4% to faunal carbon uptake (foraminifera plus macrofauna) after 14 days, despite making up 24% of the combined biomass. Both the dominance of deep-infaunal species, such as G. turgida and M. barleeanum (68%), which are known to prefer degraded over more labile material, together with their large size, which often makes foraminifera respond slower to phytodetritus deposition than the more abundant, smaller-size foraminifera, are possible reasons for the retarded response observed. Overall, results from this investigation highlight that the response of large-size foraminifera to phytodetritus deposition is very slow. In addition, the results presented provide evidence that the foraminiferal response is most likely driven by differences in foraminiferal community composition and structure, with large, deep-infaunal species showing slower reactions to phytodetritus deposition compared to smaller foraminifera, metazoan meiofauna, and macrofauna.

Live foraminifera from the open slope between Grand Rhône and Petit Rhône Canyons (Gulf of Lions, NW Mediterranean)

We present an ecological study of live (Rose Bengal stained) foraminifera from 6 deep-sea stations sampled on the open slope between the Grand Rhône Canyon and the Petit Rhône Canyon (eastern part of the Gulf of Lions, NW Mediterranean). The 6 stations describe a bathymetric transect from ∼350 to ∼2000 m depth. The main objective of our study is to investigate the changes of the foraminiferal density, composition and microhabitat along this transect in response to the physico-chemical conditions at and below the sediment–water interface. All our observations underline the general meso-oligotrophic character of our inter-canyon open-slope setting where low-quality organic matter originating from both marine and continental sources settles. The input of organic matter at the sediment–water interface leads to a classical succession of redox reactions within the sediment. The shallowest station (∼350 m) appears as an active sedimentary environment, where coarse sediments characterized by lower-quality organic matter and biogenic material accumulate. The 550-m-deep station presents bioturbated sediments with the highest concentration of labile organic compounds. The deeper stations, between about 750 and 2000 m deep, show decreasing sedimentation rates with water depth and are characterized by a background of low-quality organic matter. The foraminiferal changes recorded along the bathymetric transect are related to a complex association of physico-chemical parameters. We think that the quality of organic matter in the surficial sediment, as expressed by the lipid concentration, is the major parameter controlling the foraminiferal distribution at our open-slope stations. From the 550- to the 2000-m-deep station, the foraminiferal standing stocks and diversity decrease with depth, as a result of the increasing scarcity of labile organic compounds at the sediment–water interface. Oxygen concentration and penetration depth and the intensity of bioturbation seem to play only a secondary ecological role. Other, putative hydro-sedimentary processes (winnowing by strong bottom currents, sand-bed deposition) appear as additional parameters controlling the foraminiferal community structure. At the 350-m-deep station, the live foraminiferal fauna can be considered as a non-equilibrium assemblage thriving in frequently disturbed and food-impoverished sediments. At the 745- and 980-m-deep stations, the occurrence of suspensivorous epibenthic/epilithic species suggests the presence of strong bottom-water current velocities and the related suspension of organic particles.

A 3-stage pollution identification system with an example of final stage decimation

Abstract

Surface and deep water response to rapid climate changes at the Western Iberian Margin

Rapid climate changes at the onset of the last deglaciation and during Heinrich Event H4 were studied in detail at IMAGES cores MD95-2039 and MD95-2040 from the Western Iberian margin. A major reorganisation of surface water hydrography, benthic foraminiferal community structure, and deepwater isotopic composition commenced already 540 years before the Last Isotopic Maximum (LIM) at 17.43 cal. ka and within 670 years affected all environments. Changes were initiated by meltwater spill in the Nordic Seas and northern North Atlantic that commenced 100 years before concomitant changes were felt off western Iberia. Benthic foraminiferal associations record the drawdown of deepwater oxygenation during meltwater and subsequent Heinrich Events H1 and H4 with a bloom of dysoxic species. At a water depth of 3380 m, benthic oxygen isotopes depict the influence of brines from sea ice formation during ice-rafting pulses and meltwater spill. The brines conceivably were a source of ventilation and provided oxygen to the deeper water masses. Some if not most of the lower deep water came from the South Atlantic. Benthic foraminiferal assemblages display a multi-centennial, approximately 300-year periodicity of oxygen supply at 2470-m water depth. This pattern suggests a probable influence of atmospheric oscillations on the thermohaline convection with frequencies similar to Holocene climate variations. For Heinrich Events H1 and H4, response times of surface water properties off western Iberia to meltwater injection to the Nordic Seas were extremely short, in the range of a few decades only. The ensuing reduction of deepwater ventilation commenced within 500–600 years after the first onset of meltwater spill. These fast temporal responses lend credence to numerical simulations that indicate ocean–climate responses on similar and even faster time scales.

Territorial damselfish enhances multi-species co-existence of foraminifera mediated by biotic habitat structuring

The structures of benthic foraminiferal communities inside and outside the territory of the pomacentrid damselfish Stegastes nigricans on coral rocks in a moat of Sesoko Is. (26°38′N, 127°52′E) in Okinawa, Japan were compared. Inside the territory, an algal farm, i.e., a dense stand of a filamentous rhodophyte, Womersleyella setacea, was maintained throughout the year. Outside the territory, in areas subjected to intensive and continuous grazing by various grazers, the flora was composed of mat-like cyanophytes, a prostrate turf-form Padina sp., microscopically thin filaments and scattered filamentous rhodophytes. Algal biomass was greater inside the territory than outside the territory of the damselfish. These differences were reflected by the structure of the associated foraminiferal communities. We classified foraminiferal species based on their microhabitat use around algal communities into four life types: free-living type, crawling type, sedentary type, and sessile type. The abundance of foraminifera, especially the free-living type (e.g., Peneroplis pertusus and Quinqueloculina seminulum) and sedentary type ( Rosalina globularis and Cymbaloporetta squammosa), was greater inside the territory of the damselfish than outside the territory. Species richness was also higher inside the territory, mainly due to an increase in species richness of the free-living and sedentary types. These increases in abundance and species richness were caused by habitat structuring. W. setacea is a relatively tall and complicated alga with tangled rhizoids. Its dense stand inside the territory trapped a larger amount of sediment, which provided free-living foraminifera with heterogeneous and stable habitats. In addition, the dense stand of W. setacea provided sedentary-type foraminifera with a large, complex substratum, providing refuge and food inside the territory. This assumption was confirmed by the results of plate experiments showing that foraminiferal community structures were controlled by associations between foraminifera and algae. We showed that habitat-conditioning is an important process in biotic habitat-structuring and that habitat-conditioning by territorial damselfish maintains and enhances multi-species coexistence of foraminifera on coral rocks in a coral reef.