Développement d’un indice biotique basé sur les foraminifères benthiques ; : application sur la façade méditerranéenne française

Coastal environments suffer from anthropogenic activities. Various types of pressure can have large impacts on benthic ecosystems. In Europe, international regulations, such as the Water Framework Directive (WFD), have been implemented. The WFD aims to attain and sustain a good ecological status for all coastal waters, up to one mile from the coast. To verify whether this good status has been reached, adapted and efficient measuring tools are needed. The use of biotic indices based on foraminiferal faunas are a mean to assess the ecosystem status. The use of indices based on foraminiferal faunas rapidly increases, especially in the Mediterranean. In terms of methodology, we were able to improve a method to concentrate benthic foraminifera by density separation, which accelerates the sample treatment. The TSI-Med index includes a correction to take into account the natural trophic state, i.e., the natural enrichment rate in organic matter, on the basis of sediment grain size. However, our data suggest that the applied correction is still insufficient. We also compared several biotic indices based on benthic foraminiferal faunas along the French Mediterranean coast. Indices based on diversity, such as the exp(H’bc), are not suited for our oligotrophic study area. The results of three tested indices based on ecological groups (TSI-Med, Foram-AMBI, FSI) are well correlated. The main factor inducing differences between the indices is the list of ecological assignments for the various species. In general, too many species have not yet been assigned to ecological categories and the assignment of several major species is problematic. Nevertheless, we show that the indices are already efficient in detecting the impact of diffusive organic matter enrichment or enrichment from point sources, such as sewage outlets (Israelian coast). To further perfection the foraminiferal indices, the efforts of ecological assignments of species have to be continuedLes milieux côtiers subissent de fortes pressions dues aux activités anthropiques. Ces pressions vont parfois impacter les écosystèmes benthiques. En Europe, des réglementations internationales, telle que la Directive Cadre sur l’Eau (DCE), ont vu le jour. La DCE a fixé un cadre pour obtenir le retour et le maintien d’un bon état écologique pour les masses d’eau côtières, jusqu’à un mile de la côte. Pour vérifier si ce bon état écologique est atteint, des outils de mesure adaptés et performants sont nécessaires. L’utilisation d’indices biotiques basés sur les faunes de foraminifères benthiques est un des moyens pour mesurer l’état des écosystèmes. Ces indices basés sur les faunes de foraminifères sont en pleine expansion, notamment en Méditerranée. En termes de méthodologie, nous avons pu améliorer une technique de concentration des foraminifères benthiques par séparation par densité, qui accélère le traitement des échantillons. L’indice TSI-Med a la particularité d’apporter une correction pour l’état trophique naturel, c’est-à-dire le taux d’enrichissement naturel en matière organique, sur la base de la granulométrie du sédiment. Nos données suggèrent néanmoins que cette correction est encore insuffisante. Nous avons également comparé plusieurs indices biotiques basés sur les faunes de foraminifères benthiques le long des côtes méditerranéennes françaises. Les indices basés sur la diversité, notamment l’exp(H’bc), ne sont pas adaptés à notre zone d’étude oligotrophe. Les indices basés sur les groupes écologiques d’espèces que nous avons testés (TSI-Med, Foram-AMBI et FSI) sont plutôt bien corrélés. Le principal facteur qui va induire des différences entre ces indices est la liste d’assignation écologique des espèces. Trop d’espèces n’ont pas encore été assignées et l’assignation de plusieurs espèces majeures est problématique. Néanmoins, nous avons montré que ces indices sont efficaces à détecter l’impact d’un enrichissement en matière organique diffus et/ou provenant de source ponctuelle, telle que les rejets de stations d’épuration (côte israélienne). Pour perfectionner ces indices, des efforts de caractérisation écologique des espèces doivent être poursuivis

Development of a biotic index based on benthic foraminifera; : application in the French Mediterranean coastal waters

Les milieux côtiers subissent de fortes pressions dues aux activités anthropiques. Ces pressions vont parfois impacter les écosystèmes benthiques. En Europe, des réglementations internationales, telle que la Directive Cadre sur l’Eau (DCE), ont vu le jour. La DCE a fixé un cadre pour obtenir le retour et le maintien d’un bon état écologique pour les masses d’eau côtières, jusqu’à un mile de la côte. Pour vérifier si ce bon état écologique est atteint, des outils de mesure adaptés et performants sont nécessaires. L’utilisation d’indices biotiques basés sur les faunes de foraminifères benthiques est un des moyens pour mesurer l’état des écosystèmes. Ces indices basés sur les faunes de foraminifères sont en pleine expansion, notamment en Méditerranée. En termes de méthodologie, nous avons pu améliorer une technique de concentration des foraminifères benthiques par séparation par densité, qui accélère le traitement des échantillons. L’indice TSI-Med a la particularité d’apporter une correction pour l’état trophique naturel, c’est-à-dire le taux d’enrichissement naturel en matière organique, sur la base de la granulométrie du sédiment. Nos données suggèrent néanmoins que cette correction est encore insuffisante. Nous avons également comparé plusieurs indices biotiques basés sur les faunes de foraminifères benthiques le long des côtes méditerranéennes françaises. Les indices basés sur la diversité, notamment l’exp(H’bc), ne sont pas adaptés à notre zone d’étude oligotrophe. Les indices basés sur les groupes écologiques d’espèces que nous avons testés (TSI-Med, Foram-AMBI et FSI) sont plutôt bien corrélés. Le principal facteur qui va induire des différences entre ces indices est la liste d’assignation écologique des espèces. Trop d’espèces n’ont pas encore été assignées et l’assignation de plusieurs espèces majeures est problématique. Néanmoins, nous avons montré que ces indices sont efficaces à détecter l’impact d’un enrichissement en matière organique diffus et/ou provenant de source ponctuelle, telle que les rejets de stations d’épuration (côte israélienne). Pour perfectionner ces indices, des efforts de caractérisation écologique des espèces doivent être poursuivis.Coastal environments suffer from anthropogenic activities. Various types of pressure can have large impacts on benthic ecosystems. In Europe, international regulations, such as the Water Framework Directive (WFD), have been implemented. The WFD aims to attain and sustain a good ecological status for all coastal waters, up to one mile from the coast. To verify whether this good status has been reached, adapted and efficient measuring tools are needed. The use of biotic indices based on foraminiferal faunas are a mean to assess the ecosystem status. The use of indices based on foraminiferal faunas rapidly increases, especially in the Mediterranean. In terms of methodology, we were able to improve a method to concentrate benthic foraminifera by density separation, which accelerates the sample treatment. The TSI-Med index includes a correction to take into account the natural trophic state, i.e., the natural enrichment rate in organic matter, on the basis of sediment grain size. However, our data suggest that the applied correction is still insufficient. We also compared several biotic indices based on benthic foraminiferal faunas along the French Mediterranean coast. Indices based on diversity, such as the exp(H’bc), are not suited for our oligotrophic study area. The results of three tested indices based on ecological groups (TSI-Med, Foram-AMBI, FSI) are well correlated. The main factor inducing differences between the indices is the list of ecological assignments for the various species. In general, too many species have not yet been assigned to ecological categories and the assignment of several major species is problematic. Nevertheless, we show that the indices are already efficient in detecting the impact of diffusive organic matter enrichment or enrichment from point sources, such as sewage outlets (Israelian coast). To further perfection the foraminiferal indices, the efforts of ecological assignments of species have to be continue

An optimised method to concentrate living (Rose Bengal-stained) benthic foraminifera from sandy sediments by high density liquids

International audienceIn recent years, living (Rose Bengal-stained) benthic foraminifera are increasingly used in biomonitoring studies, with the international expert group FOBIMO proposing the development of standardised methods. Until now, it has been considered inadvisable to concentrate foraminifera by density separation, because this may bias the composition of the foraminiferal fauna, and does not offer sufficient quantitative guarantees. However, biomonitoring studies often concern coastal areas with sandy sediments where living foraminifera are diluted by large amounts of sediment grains. Hence, long picking times are a serious economical setback, strongly limiting the use of foraminifera in environmental quality assessment. We aimed to select, on the basis of quantitative criteria, the best available density separation method, capable of strongly concentrating living foraminifera without a significant change in the faunal composition. We selected three test samples, from the French Mediterranean coast, with different sediment particle types and foraminiferal faunas (with a high contribution of agglutinated taxa, not well separated in earlier studies). We tested three high density solutions: trichloroethylene (TCE), zinc chloride (ZC), and sodium polytungstate (SPT). Although TCE is a highly toxic organic compound, it was commonly used in the past. We compared its efficiency with that of two salts (ZC and SPT), dissolved in water, so that their density can be easily adjusted. We tested SPT with a range of density values (i.e., 1.7, 2.1, 2.3, and 2.5). The deposited and floated parts of each processed sample were both carefully scrutinised for Rose Bengal-stained foraminifera. The rather low density of TCE (1.46) led to poor foraminiferal recovery rates (30–50%). ZC reacted with calcite-rich sediment, hampering a perfect separation. In spite of its high price, SPT appears to be the optimal product; at higher densities (≥ 2.1), it showed foraminiferal recovery rates ≥ 95%. However, at a density of 2.5, considerably more sediment particles (> 20%) were recovered, whereas foraminiferal recovery only marginally improved. We calculated several diversity and faunal indices both for floated fractions and total samples, and observed no differences for densities ≥ 2.3. Also, the relative frequencies of groups with different wall structures and of indicator taxa (stress-tolerant, stress-sensitive) showed only very minor differences between floated fractions and total samples for SPT at densities ≥ 2.3. In conclusion, our study shows that density separation using SPT at a density of 2.3 is a perfect method to concentrate living foraminifera from sandy sediments in biomonitoring studies

Grain size analyses and organic matter content of bottom sediment sampled along the French Mediterranean coast in 2015

The stations were sampled along the French Mediterranean coast in spring (March-April) 2015 onboard the RV Europe. Bottom sediment at 28 stations (11 to 64 m water depth) was sampled using a Reineck box-corer. Three replicates (“a”, “b”, “c”; different box-corer launches) were done at each station for meiofauna analysis. Surface sediment (0-1 cm) from the first box-corer launch (i.e., “a”) was sampled and put into plastic bags. If the sediment appears visually very different in the second and/or third launches (i.e., “b” and “c”) another sample was taken. At the laboratory, three aliquots of each sample were homogenised with a mixer mill, without ball, at 17 Hz for 2 min. Then, aliquots were sieved on a 2 mm mesh and analysed with a Malvern Mastersizer 3000 for grain size analysis. Three measures were performed for each aliquot. The organic matter percentage was determined with the loss on ignition method, 4h30 at 450 °C. These data were acquired thanks to Pierre Boissery and the funding from the Agence de l'Eau Rhône Méditerranée Corse. The sampling survey was possible thanks to the Ifremer, especially Bruno Andral, and the RV Europe crew members

Benthic foraminiferal responses to anthropogenic manipulation on a wild oyster reef

International audienceBenthic foraminifera are known to respond quickly to environmental changes. Biological indices are used in marine subtidal areas (Barras et al., 2014) to monitor impacted marine environments (Mojtahid et al., 2006, 2008). Such indices could be useful in transitional marine environments such as estuaries and mudflats where no accurate indices are available. To develop such to ols and to improve our knowledgeon b enthic foraminifera in intertidal environments, we followed the spatial and temporal distribution of b enthic foraminifera in Bourgneuf Bay, a coastal bay with a large mudflat situated south of the Loire estuary on French west coast. At this location, wild oyster reefs are present. Partial release of organicand inorganic nutrients through oyster excretion enriches the nutrients flow leading to microphytobenthosbloom around the reef. To show this relation and to understand the relation between the different biological compartments,we analysed the foraminiferal composition of the sediment around the reef before and after ananthrop ogenic manipulation. In July 2014, the oysters of the reef were removed inorder to assess their impact on microphytob enthos and meiofauna. In this study, we showed a strong impact of this anthrop ogenic manipulation on benthic foraminiferal densities and species composition.These results confirmed the strong and quick responses of benthic foraminifera from intertidal areas toenvironmental changes and showed that intertidal benthic foraminifera can be used as an index to monitor transitional marine environments.</p

Testing foraminiferal environmental quality indices along a well-defined organic matter gradient in the Eastern Mediterranean

International audienc

Study of benthic foraminiferal faunas along the French Mediterranean coasts: a new biotic index in the EU Water Framework Directive

International audienc

Grain size analyses and organic matter content of bottom sediment sampled along the French Mediterranean coast in 2012

The stations were sampled along the French Mediterranean coast in spring (March-April) 2012 onboard the RV Europe. Bottom sediment at 36 stations (10 to 71 m water depth) was sampled using a Reineck box-corer. Three replicates (“a”, “b”, “c”; different box-corer launches) were done at each station for meiofauna analysis. The surface sediment (0-1 cm) of the first box-corer launches (i.e., “a”) was used for grain size analysis. If the sediment appears visually very different in the second and third launches (i.e., “b” and “c”) another sample was taken. Sediment was sampled from the three replicates box-corer and gathered to measure grain sizes thanks to sieves. Sediment samples were first dry weighted, then wet sieved on 63, 125, 150, 250, and 500 µm meshes and finally residues were dry weighted. Then, the percentage from the total dry weight was calculated for each size fraction. Sediment from a Van Veen grab launch, deployed at each station, was used to measure organic matter content. The organic matter percentage was determined with the loss on ignition method, 4h30 at 450 °C. Missing values means not available. These data were acquired thanks to Pierre Boissery and the funding from the Agence de l'Eau Rhône Méditerranée Corse. The sampling survey was possible thanks to the Ifremer, especially Bruno Andral, and the RV Europe crew members

Living (RB-stained) benthic foraminiferal fauna sampled along the French Mediterranean coast in 2012

The stations were sampled along the French Mediterranean coast in spring (March-April) 2012 onboard the RV Europe. Bottom sediment at 36 stations (between 10 and 71 m water depth) was sampled using a Reineck box-corer. Three replicates (“a”, “b”, “c”; different box-corer launches) were done at each station. Each box-corer was sub-cored with a 7.4 cm diameter tube. Only the first top centimetre was preserved in 96% ethanol and stained with 2 g/L Rose Bengal. At the laboratory, after minimum two weeks each sample was washed through four sieves of 63, 125, 150, and 500 µm mesh sizes. Living (stained) benthic foraminifera from the 125-150 µm and 150-500 µm were collected under stereomicroscope and preserved in micropaleontological slides. Taxonomical recognition was done to the species level. The presented data in the table indicate the raw densities of foraminifera sorted per sample. The exact volume of sampled sediment was measured for each sample

Sediment migrations drive the dynamic of macrobenthic ecosystems in subtidal sandy bedforms

A traditional taxonomic approach coupled to a biological traits analysis was conducted in order to provide a new insight into macrobenthic communities associated with subtidal sandy environments. Results suggest that the macro-scale distribution of benthic communities is mainly driven by the migration rate of bedforms (sandbank, barchan dune and transversal dune) which changes the sediment grain size and reduces macrobenthic diversity. A classic scheme of species/traits succession was also observed from less to more physically disturbed areas. Finally, the high frequency of migration events homogenized macrobenthic communities between the troughs to the crest of bedforms. As bedforms areas are targeted for the commissioning of offshore windfarms the information provided by the present paper will be particularly useful to implement the environmental impact assessment required for such activities at sea