Eric Armynot du Châtelet

Testing benthic foraminiferal distributions as a contemporary quantitative approach to biomonitoring estuarine heavy metal pollution

Biomonitoring of estuarine pollution is the subject of active research, and benthic foraminifera are an attractive group to use for these purposes due to their ubiquitous presence in saline water and wide diversity. Here, we describe a case study of biomonitoring using benthic foraminifera in the French Mediterranean lagoon, Bages-Sigean lagoon. In this case, the major pollutants of interest are heavy metals in the sediment, particularly contaminated by Cu and Cd derived from industrial and agricultural sources. The foraminiferal assemblages of the Bages-Sigean lagoon are typical of normal paralic environments, but unusually almost completely lack agglutinated forms. The density of benthic foraminifera was shown to be more influenced by the sediment characteristics rather than heavy metal pollution. However, the relative abundance of Quinqueloculina bicostata was shown to increase in the most polluted areas and we propose that this taxon may be used as an indicator of heavy metal pollution.

Coastal pollution monitoring: Foraminifera as tracers of environmental perturbation in the port of Boulogne-sur-Mer (Northern France)

Abstract: Benthic foraminifera are increasingly used as environmental indicators of natural and/ or anthropogenic stress in coastal and marginal marine settings. A study of both living (Rose Bengal stained) and dead foraminifera was carried on 317 sediment samples collected in the port of Boulogne-sur-Mer (France). Here we present an initial status report on the port ecosystem as recorded from a selected set of sediment samples that cover the full range of habitats within the port. A surprisingly high diversity assemblage of benthic foraminifera was recovered, reflecting the varied habitats within the port. Among the total of 82 species recorded, 34 were found alive (rose Bengal stained). Four key species were identified as potential bioindicators and analyzed with regard to their distribution and correspondence with environmental parameters (sediment grain size, organic carbon content and heavy metal concentration, Cr, Cu and Zn). The benthic foraminifera Haynesina germanica and Bolivina pseudoplicata were found to live particularly well within the innermost parts of the port basins where the highest concentrations of organic carbon and heavy metals occur. Elphidium excavatum and E. magellanicum are well represented in the external parts of the port and can be considered as indicators that tolerate certain threshold values of pollution and environmental stress. As the port is located in an estuarine setting, the relationship between the key indicator taxa for pollution and natural environment is discussed. This study emphasizes the need to address the anthropogenic impact on coastal environments by screening the ubiquitous record of foraminiferal protists as precision tools for bio-monitoring.

Multiproxy approach for Holocene paleoenvironmental reconstructions from microorganisms (testate amoebae and foraminifera) and sediment analyses: The infilling of the Loire Valley in Nantes (France)

Foraminifera and testate amoebae are jointly used with sediment characteristics (sediment size, calcium carbonate, C, H, N and S proportions, and clay mineralogy) to reconstruct the Holocene sediment infilling of the Loire estuary (Nantes, France). The results reveal the infilling of the Loire Valley during the Holocene. Deposited on the Hercynian substratum, the first deposits are made of gravels with rare associated fauna. This corresponds to the gravel lag usually present as basal deposits in the river course. The clay mineralogy indicates an erosion of the substratum. Then, from 8850 to 5850 cal. yr BP, estuarine fauna settled in a laminated sediment that alternates between clay and sand. The smectite associated with kaolinite and illite suggests increased input from the Sèvre Nantaise River. The fauna progressively shifts from estuarine to marine, indicating a rise in the sea level. From 5850 cal. yr BP, the pace of the sea level rise slowed and channels migrated, implying intense erosion. After 2100 cal. yr BP, the fauna was dominated by testate amoebae, indicating a continentalization of the environment. The top samples reflect recent human activity and urbanization.

Foraminiferal and testate amoeba diversity, distribution and ecology in transitional environments of the Tramandaí Basin (Rio Grande do Sul, South Brazil)

In order to document benthic foraminiferal and testate amoeba diversity, a total of 115 sediment samples were collected from nine different transitional environments along a 100-km long coastal area located in Rio Grande do Sul (Brazil). This area is directly affected by both the input of freshwater from the Tramandaí River and a marine influence due to its proximity to the Atlantic Ocean. In particular, 14 and 101 species are recognized within the benthic foraminiferal and testate amoeba assemblages, respectively. Testate amoebae diversity is significantly higher than that documented in previous investigations carried out in other parts of the Brazilian coast. The two dominant testate amoeba families are Difflugidae and Hyalospheniidae, which are represented by 74 and 9 species, respectively. On the other hand, the benthic foraminiferal assemblages are poorly diversified and mainly dominated by agglutinated forms that are typical of transitional environments under the direct influence of a freshwater input. The distribution of these two groups characterizes both the freshwater environments, where testate amoebae are the only representatives, and the more marine conditions, where benthic foraminifera tend to dominate the benthic community, and allows the recognition of a marine influence gradient. The benthic foraminiferal assemblages are mainly observed in front of the direct opening to the sea, but are completely absent in the innermost environments, whereas testate amoebae are more widely distributed, albeit in variable abundances, but are completely missing close to the Tramandaí Basin’s outlet. Although the diversity of the benthic community in South Atlantic coastal regions is difficult to determine, this study represents, to our knowledge, the first investigation of benthic foraminifera and testate amoebae along the 100-km long coastal area, characterized by lagoons and lakes interconnected by canals and small rivers.

Environmental control on a land–sea transitional setting: integrated sedimentological, geochemical and faunal approaches

Because of their location at the interface between sea and emerged lands, so-called transitional environments are characterized by strong spatial and temporal variability in terms of sedimentological, physicochemical, and geochemical parameters. An increasing number of studies put forward the use of bioindicators as a tool for environmental monitoring. However, the sensitivity to these environmental parameters is commonly tested separately, even though it is known that interactions are numerous within this complex ecosystem. An integrated methodological study was conducted in Lake Varano (Italy). On the basis of 45 spatially distributed samples throughout the area and selected environmental parameters (trace elements, organic matter, clay mineral assemblages, grain size of sediment, and water characteristics), four factors are identified. The Lake Varano ecosystem is predominantly influenced by terrigenous inputs (first-order factor). The clastic fractions of the sediments supply a large range of trace elements, occasionally in relatively high concentrations. Under such circumstances, despite occasionally exceeding of threshold limits, the trace element pollution can generally be ruled out. The organic content combined with depth is the second key factor. In Lake Varano, the organic content is high and may lead to seasonal eutrophication. As a third-order factor, although only analyzed once, oxygen, ORP, salinity, and pH gradients show that foraminiferal diversity is positively influenced by more saline conditions. The fourth-order factor is the sediment size. To conclude, this paper illustrates the interest in and need to conduct a detailed, integrated, sedimentological study of a site prior to any examination of its ecological status (possible occurrences of sources of pollution).

Three-dimensional morphological and mineralogical characterization of testate amebae.

Testate amebae are unicellular shelled protozoa commonly used as indicators in ecological and paleoecological studies. We explored the potential application of three-dimensional (3D) X-ray micro-tomography used in addition to 2D techniques (environmental scanning electron microscopy, electron probe micro-analysis, and cathodoluminescence) for detailed characterization of agglutinated shells of protozoa. We analyzed four specimens of the aquatic testate ameba Difflugia oblonga (Arcellinida), to test whether size distribution and mineral composition of shell grains diverged from sediment size distribution and mineralogical composition. From the 3D images, the geometry of the specimens (size and mass) and of the individual grains forming the specimen (grain size distribution and volume) were calculated. Based on combined chemical, mineralogical, and morphological analyses we show that D. oblonga is able to selectively pick up the small size fraction of the sediment with a preference for low-density silicates close to quartz density (~2.65). The maximum size of the grains matches the size of the pseudostome (shell aperture), suggesting the existence of a physical limit to grain size used for building the shell. This study illustrates the potential of this combined approach to characterize agglutinated shells of protozoa. This data can be useful for detailed morphological studies with applications in taxonomy and ecology.

Assessing the effect of mercury pollution on cultured benthic foraminifera community using morphological and eDNA metabarcoding approaches

Mercury (Hg) is a highly toxic element for living organisms and is known to bioaccumulate and biomagnify. Here, we analyze the response of benthic foraminifera communities cultured in mesocosm and exposed to different concentrations of Hg. Standard morphological analyses and environmental DNA metabarcoding show evidence that Hg pollution has detrimental effects on benthic foraminifera. The molecular analysis provides a more complete view of foraminiferal communities including the soft-walled single-chambered monothalamiids and small-sized hard-shelled rotaliids and textulariids than the morphological one. Among these taxa that are typically overlooked in morphological studies we found potential bioindicators of Hg pollution. The mesocosm approach proves to be an effective method to study benthic foraminiferal responses to various types and concentrations of pollutants over time. This study further supports foraminiferal metabarcoding as a complementary and/or alternative method to standard biomonitoring program based on the morphological identification of species communities.

Cinderella's helping pigeons of the microbial world: The potential of testate amoebae for identifying cryptotephra

Cryptotephra (particles <125μm) is a key record for monitoring past and current volcanic activity. However, its extraction from the host sediment and analysis is often long and difficult because of its small size. Finding a simple method to extract cryptotephra from environmental samples would therefore make its analysis much easier. We hypothesized that arcellinid testate amoebae may hold such a potential. These free-living shelled protists are among the earliest microorganisms to colonize volcanic tephra, and build their shell by agglutinating minerals from their environment. We analyzed by X-ray Spectrometry the mineral signature of tephra from the 2011 Puyehue-Cordon Caulle Volcanic Complex (Chile) eruption ash fallout and compared it to that of the shells of 51 individual testate amoebae (three individuals from each of 17 species) from 13 samples collected at different distances from the active vent. The mineral composition of particles within shells closely matched that of similar size class particles from their environment. The capacity of testate amoebae to randomly use mineral grains from their environment makes it possible to use their shells to assess the mineral composition of cryptotephra from soil, peat or sediment samples. Testate amoebae therefore represent the microbial worlds version of Cinderellas helping pigeons.

Biodiversity and distribution of the meiofaunal community in the reef slopes of the Maldivian archipelago (Indian Ocean)

Marine biologists have progressively increased their consciousness of the importance of meiofauna for the benthic domain in both temperate and tropical regions. After the 1998 bleaching, Maldivian reefs (Indian Ocean) have been regarded as a vulnerable ecosystem that must be carefully monitored. Accordingly, an extensive investigation of meiofaunal distribution in the reef slopes of the Maldivian archipelago has been carried out, taking into account geographical position, type of habitat (inner vs. outer slope), inclination and depth gradient. Twenty-four taxa revealed the highest meiofaunal richness ever found in Maldivian reefs. Interestingly, Thermosbenacea and Syncarida were identified, which are two taxa that have only recently been documented in the marine ecosystem. Chaetognatha were also present, which is a group that was only considered to be planktonic until 2000, when they were also discovered in the benthos. The type of habitat, affected by different hydrodynamic conditions, was the main factor influencing the meiofaunal communitys structure and diversity. In detail, the outer reefs were characterized by the highest level of diversity, confirming previous observations on the rate of coral reef growth and vitality and underlining the greater vulnerability of the inner slopes. In contrast, depth only significantly affected the community structure, but not its density or diversity. Accordingly, community structure seems to be more sensitive than abundance and diversity indices when it comes to detecting depth gradients. The 10° inclination of the inner slopes revealed the most different community structure and the greatest dominance of nematodes, leading to the lowest diversity levels.

The response of cultured meiofaunal and benthic foraminiferal communities to lead exposure: Results from mesocosm experiments

Lead (Pb) is regarded as a highly toxic element that poses a serious threat to biota. A mesocosm experiment was performed to assess the influence of Pb on meiofaunal (metazoans within 45-500 μm) and benthic foraminiferal (protozoan) communities. To this end, sediments bearing such communities were incubated in mesocosms, exposed to different levels of Pb in seawater, and monitored for up to 8 wk. Concentrations of Pb <1 ppm in water did not promote a significant increase of this metal in sediments. Relatively high concentrations of Pb seemed to affect meiofaunal and benthic foraminiferal communities by reducing their richness or diversity, and the abundance of the most sensitive taxa. The mesocosm approach can be considered an effective method to document the responses of meiofaunal and benthic foraminiferal communities to various kinds and concentrations of pollutants over time. This approach allows the evaluation of dose-response relationships, validates the outcomes of field studies, and possibly confirms the sediment quality guidelines and thresholds. Environ Toxicol Chem 2018;37:2439-2447.