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Philippe Esling

Postdoctoral fellow in Molecular Systematics & Environmental Genomics

  • T: +41 22 379 30 77
  • office 4078b (Sciences III)
  • Predicting the ecological quality status of marine environments from eDNA metabarcoding data using supervised machine learning. Environ. Sci. Technol. 2017 Jun;():. 10.1021/acs.est.7b01518.

    abstract

    Monitoring biodiversity is essential to assess the impacts of increasing anthropogenic activities in marine environments. Traditionally, marine biomonitoring involves the sorting and morphological identification of benthic macro-invertebrates, which is time-consuming and taxonomic-expertise demanding. High-throughput amplicon sequencing of environmental DNA (eDNA metabarcoding) represents a promising alternative for benthic monitoring. However, an important fraction of eDNA sequences remains unassigned or belong to taxa of unknown ecology, which prevent their use for assessing the ecological quality status. Here, we show that supervised machine learning (SML) can be used to build robust predictive models for benthic monitoring, regardless of the taxonomic assignment of eDNA sequences. We tested three SML approaches to assess the environmental impact of marine aquaculture using benthic foraminifera eDNA, a group of unicellular eukaryotes known to be good bioindicators, as features to infer macro-invertebrates based biotic indices. We found similar ecological status as obtained from macro-invertebrates inventories. We argue that SML approaches could overcome and even bypass the cost and time-demanding morpho-taxonomic approaches in future biomonitoring.

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  • Taxonomy-free molecular diatom index for high-throughput eDNA biomonitoring. Mol Ecol Resour 2017 Mar;():. 10.1111/1755-0998.12668.

    abstract

    Current biodiversity assessment and biomonitoring are largely based on the morphological identification of selected bioindicator taxa. Recently, several attempts have been made to use eDNA metabarcoding as an alternative tool. However, until now, most applied metabarcoding studies have been based on the taxonomic assignment of sequences that provides reference to morphospecies ecology. Usually, only a small portion of metabarcoding data can be used due to a limited reference database and a lack of phylogenetic resolution. Here, we investigate the possibility to overcome these limitations by using a taxonomy-free approach that allows the computing of a molecular index directly from eDNA data without any reference to morphotaxonomy. As a case study, we use the benthic diatoms index, commonly used for monitoring the biological quality of rivers and streams. We analysed 87 epilithic samples from Swiss rivers, the ecological status of which was established based on the microscopic identification of diatom species. We compared the diatom index derived from eDNA data obtained with or without taxonomic assignment. Our taxonomy-free approach yields promising results by providing a correct assessment for 77% of examined sites. The main advantage of this method is that almost 95% of OTUs could be used for index calculation, compared to 35% in the case of the taxonomic assignment approach. Its main limitations are under-sampling and the need to calibrate the index based on the microscopic assessment of diatoms communities. However, once calibrated, the taxonomy-free molecular index can be easily standardized and applied in routine biomonitoring, as a complementary tool allowing fast and cost-effective assessment of the biological quality of watercourses. This article is protected by copyright. All rights reserved.

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  • Benthic monitoring of salmon farms in Norway using foraminiferal metabarcoding AEI 8:371-386 (2016) - doi:10.3354/aei00182

    abstract

    The rapid growth of the salmon industry necessitates the development of fast and accurate tools to assess its environmental impact. Macrobenthic monitoring is commonly used to measure the impact of organic enrichment associated with salmon farm activities. However, classical benthic monitoring can hardly answer the rapidly growing demand because the morphological identification of macro-invertebrates is time-consuming, expensive and requires taxonomic expertise. Environmental DNA (eDNA) metabarcoding of meiofauna-sized organisms, such as Foraminifera, was proposed to overcome the drawbacks of macrofauna-based benthic monitoring. Here, we tested the application of foraminiferal metabarcoding to benthic monitoring of salmon farms in Norway. We analysed 140 samples of eDNA and environmental RNA (eRNA) extracted from surface sediment samples collected at 4 salmon farming sites in Norway. We sequenced the variable region 37f of the 18S rRNA gene specific to Foraminifera. We compared our data to the results of macrofaunal surveys of the same sites and tested the congruence between various diversity indices inferred from metabarcoding and morphological data. The results of our study confirm the usefulness of Foraminifera as bioindicators of organic enrichment associated with salmon farming. The foraminiferal diversity increased with the distance to fish cages, and metabarcoding provides an assessment of the ecological quality comparable to the morphological analyses. The foraminiferal metabarcoding approach appears to be a promising alternative to classical benthic monitoring, providing a solution to the morpho-taxonomic bottleneck of macrofaunal surveys.

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  • Protist metabarcoding and environmental biomonitoring: Time for change. Eur. J. Protistol. 2016 Aug;55(Pt A):12-25. S0932-4739(16)30003-7. 10.1016/j.ejop.2016.02.003.

    abstract

    High-throughput amplicon sequencing of environmental DNA and/or RNA proved to be a powerful tool to describe protist diversity. This new approach called also the metabarcoding has totally transformed our view of protist diversity, revealing a large number of novel lineages and expanding the range of protist phylogenetic diversity at almost every taxonomic level. However, until now the objectives of the vast majority of metabarcoding studies were purely academic. Practical applications of protist metabarcoding are surprisingly scarce, despite the fact that several groups of protists are commonly used as bioindicators of environmental impacts in freshwater or marine ecosystems. Here, we are reviewing studies that examine the ecological applications of metabarcoding for two groups of well-known protist bioindicators: diatoms and foraminifera. The results of these studies show that despite some biological and technical biases, molecular data quite faithfully reflect the morphology-based biotic indices and provide a similar assessment of ecosystem status. In view of these results, protist metabarcoding appears as a rapid and accurate tool for the evaluation of the quality of aquatic ecosystems. Hence, we plead for integration of protist metabarcoding in future biomonitoring projects as a complement of traditional methods and a source of new biosensors for environmental impact assessment.

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  • High-throughput sequencing and morphology perform equally well for benthic monitoring of marine ecosystems. Sci Rep 2015 ;5():13932. srep13932. 10.1038/srep13932. PMC4564730.

    abstract

    Environmental diversity surveys are crucial for the bioassessment of anthropogenic impacts on marine ecosystems. Traditional benthic monitoring relying on morphotaxonomic inventories of macrofaunal communities is expensive, time-consuming and expertise-demanding. High-throughput sequencing of environmental DNA barcodes (metabarcoding) offers an alternative to describe biological communities. However, whether the metabarcoding approach meets the quality standards of benthic monitoring remains to be tested. Here, we compared morphological and eDNA/RNA-based inventories of metazoans from samples collected at 10 stations around a fish farm in Scotland, including near-cage and distant zones. For each of 5 replicate samples per station, we sequenced the V4 region of the 18S rRNA gene using the Illumina technology. After filtering, we obtained 841,766 metazoan sequences clustered in 163 Operational Taxonomic Units (OTUs). We assigned the OTUs by combining local BLAST searches with phylogenetic analyses. We calculated two commonly used indices: the Infaunal Trophic Index and the AZTI Marine Biotic Index. We found that the molecular data faithfully reflect the morphology-based indices and provides an equivalent assessment of the impact associated with fish farms activities. We advocate that future benthic monitoring should integrate metabarcoding as a rapid and accurate tool for the evaluation of the quality of marine benthic ecosystems.

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  • Accurate assessment of the impact of salmon farming on benthic sediment enrichment using foraminiferal metabarcoding. Mar. Pollut. Bull. 2015 Nov;100(1):370-82. S0025-326X(15)00526-3. 10.1016/j.marpolbul.2015.08.022.

    abstract

    Assessing the environmental impact of salmon farms on benthic systems is traditionally undertaken using biotic indices derived from microscopic analyses of macrobenthic infaunal (MI) communities. In this study, we tested the applicability of using foraminiferal-specific high-throughput sequencing (HTS) metabarcoding for monitoring these habitats. Sediment samples and physico-chemical data were collected along an enrichment gradient radiating out from three Chinook salmon (Oncorhynchus tshawytscha) farms in New Zealand. HTS of environmental DNA and RNA (eDNA/eRNA) resulted in 1,875,300 sequences that clustered into 349 Operational Taxonomic Units. Strong correlations were observed among various biotic indices calculated from MI data and normalized fourth-root transformed HTS data. Correlations were stronger using eRNA compared to eDNA data. Quantile regression spline analyses identified 12 key foraminiferal taxa that have potential to be used as bioindicator species. This study demonstrates the huge potential for using this method for biomonitoring of fish-farming and other marine industrial activities.

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  • Palaeoceanographic changes in Hornsund Fjord (Spitsbergen, Svalbard) over the last millennium: new insights from ancient DNA

    abstract

    This paper presents the reconstruction of climate-driven environmental changes of the last millennium from Hornsund Fjord (Svalbard) based on sedimentological and micropalaeontological records. Our palaeo-investigation was supported by the analysis of 5 foraminiferal ancient DNA (aDNA), focusing on non-fossilised monothalamous species. The main climatic fluctuations over the last millennium were the Medieval Warm Period (MWP, 1000–1600 AD), the Little Ice Age (LIA, 1600–1900 AD), and the Modern Warming (MW, 1900 AD–present). Our study indicated that environmental conditions in Hornsund during the MWP and the early LIA (before ∼ 1800 AD) were relatively 10 stable, resulting from the distant position of glaciers. The beginning of the LIA (∼ 1600 AD) was poorly evidenced by the micropalaeontological record, but well marked in the aDNA data, by an increased proportion of monothalamous foraminifera, especially Bathysiphon sp. The early LIA (∼ 1600–∼ 1800 AD) was marked by the increase in abundance of sequences of Hippocrepinella hirudinea and Cedhagenia saltatus. In the 15 late LIA (after ∼ 1800 AD), conditions in the fjord became glacier-proximal, characterised by increased meltwater outflows, high sedimentation and a high calving rate. This coincided with an increase in the percentages of sequences of Micrometula sp. and Vellaria pellucidus. During the MW, major glaciers fronts retreated rapidly to the inner bays, limiting the iceberg discharge to the fjord centre and causing the shift in the 20 foraminiferal community reflected in both fossil and aDNA records. Palaeoceanographic changes in the Hornsund Fjord over the last millennium were driven mainly by the inflow of shelf-originated water masses and glaciers’ activity. However, the environmental changes were poorly evidenced in the micropalaeontological record, but well documented in our aDNA data. We considerably increased the number 25 of potential proxy species by including monothalamous foraminifera in the palaeoecological studies.

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  • Palaeoceanographic changes in Hornsund Fjord (Spitsbergen, Svalbard) over the last millennium: new insights from ancient DNA Climate of the Past Discussions 11, 3665-3698; 10.5194/cpd-11-3665-2015

    abstract

    This paper presents a reconstruction of climatedriven environmental changes over the last millennium in Hornsund Fjord (Svalbard), based on sedimentological and micropalaeontological records. Our palaeo-investigation was supported by an analysis of foraminiferal ancient DNA (aDNA), focusing on the non-fossilized monothalamous species. The main climatic fluctuations during the last millennium were the Medieval Warm Period (MWP, AD 1000– 1600), the Little Ice Age (LIA, AD 1600–1900) and the modern warming (MW, AD 1900 to present). Our study indicates that the environmental conditions in Hornsund during the MWP and the early LIA (before ∼ AD 1800) were relatively stable. The beginning of the LIA (∼ AD 1600) was poorly evidenced by the micropalaeontological record but was well marked in the aDNA data by an increased proportion of monothalamous foraminifera, especially Bathysiphon sp. The early LIA (∼ 1600 to ∼ AD 1800) was marked by an increase in the abundance of sequences of Hippocrepinella hirudinea and Cedhagenia saltatus. In the late LIA (after ∼ AD 1800), the conditions in the fjord became glacierproximal and were characterized by increased meltwater out- flows, high sedimentation and a high calving rate. This coincided with an increase in the percentages of sequences of Micrometula sp. and Vellaria pellucidus. During the MW, the major glacier fronts retreated rapidly to the inner bays, which limited the iceberg discharge to the fjord’s centre and caused a shift in the foraminiferal community that was reflected in both the fossil and aDNA records.

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  • Environmental Monitoring: Inferring the Diatom Index from Next-Generation Sequencing Data. Environ. Sci. Technol. 2015 Jul;49(13):7597-605. 10.1021/es506158m.

    abstract

    Diatoms are widely used as bioindicators for the assessment of water quality in rivers and streams. Classically, the diatom biotic indices are based on the relative abundance of morphologically identified species weighted by their autoecological value. Obtaining such indices is time-consuming, costly, and requires excellent taxonomic expertise, which is not always available. Here we tested the possibility to overcome these limitations using a next-generation sequencing (NGS) approach to identify and quantify diatoms found in environmental DNA and RNA samples. We analyzed 27 river sites in the Geneva area (Switzerland), in order to compare the values of the Swiss Diatom Index (DI-CH) computed either by microscopic quantification of diatom species or directly from NGS data. Despite gaps in the reference database and variations in relative abundance of analyzed species, the diatom index shows a significant correlation between morphological and molecular data indicating similar biological quality status for the majority of sites. This proof-of-concept study demonstrates the potential of the NGS approach for identification and quantification of diatoms in environmental samples, opening new avenues toward the routine application of genetic tools for bioassessment and biomonitoring of aquatic ecosystems.

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  • Accurate multiplexing and filtering for high-throughput amplicon-sequencing. Nucleic Acids Res. 2015 Mar;43(5):2513-24. gkv107. 10.1093/nar/gkv107. PMC4357712.

    abstract

    Tagging amplicons with tag sequences appended to PCR primers allow the multiplexing of numerous samples for high-throughput sequencing (HTS). This approach is routinely used in HTS-based diversity analyses, especially in microbial ecology and biomedical diagnostics. However, amplicon library preparation is subject to pervasive sample sequence cross-contaminations as a result of tag switching events referred to as mistagging. Here, we sequenced seven amplicon libraries prepared using various multiplexing designs in order to measure the magnitude of this phenomenon and its impact on diversity analyses. Up to 28.2% of the unique sequences correspond to undetectable (critical) mistags in single- or saturated double-tagging libraries. We show the advantage of multiplexing samples following Latin Square Designs in order to optimize the detection of mistags and maximize the information on their distribution across samples. We use this information in designs incorporating PCR replicates to filter the critical mistags and to recover the exact composition of mock community samples. Being parameter-free and data-driven, our approach can provide more accurate and reproducible HTS data sets, improving the reliability of their interpretations.

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  • Patchiness of deep-sea benthic Foraminifera across the Southern Ocean: insights from high-throughput DNA sequencing 10.1016/j.dsr2.2014.07.018

    abstract

    Spatial patchiness is a natural feature that strongly influences the level of species richness we perceive in surface sediments sampled in the deep-sea. Recent environmental DNA (eDNA) surveys of benthic micro- and meiofauna confirmed this exceptional richness. However, it is unknown to which extent the results of these studies, based usually on few grams of sediment, are affected by spatial patchiness of deep-sea benthos. Here, we analyse the eDNA diversity of Foraminifera in 42 deep-sea sediment samples collected across different scales in the Southern Ocean. At three stations, we deployed at least twice the multicorer and from each multicorer cast, we subsampled 3 sediment replicates per core for 2 cores. Using high-throughput sequencing (HTS), we generated over 2.35 million high-quality sequences that we clustered into 451 operational taxonomic units (OTUs). The majority of OTUs were assigned to the monothalamous (single-chambered) taxa and environmental clades. On average, a one-gram sediment sample captures 57.9% of the overall OTU diversity found in a single core, while three replicates cover at most 61.9% of the diversity found in a station. The OTUs found in all the replicates of each core gather up to 87.9% of the total sequenced reads, but only represent from 12.2% to 30% of the OTUs found in one core. These OTUs represent the most abundant species, among which dominate environmental lineages. The majority of the OTUs are represented by few sequences comprising several well-known deep-sea morphospecies or remaining unassigned. It is crucial to study wider arrays of sample and PCR replicates as well as RNA together with DNA in order to overcome biases stemming from deep-sea patchiness and molecular methods.

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  • Patchiness of deep-sea benthic Foraminifera across the southern ocean: Insights from High-throughput DNA sequencing http://dx.doi.org/10.1016/j.dsr2.2014.07.018

    abstract

    Spatial patchiness is a natural feature that strongly influences the level of species richness we perceive in surface sediments sampled in the deep-sea. Recent environmental DNA (eDNA) surveys of benthic micro- and meiofauna confirmed this exceptional richness. However, it is unknown to which extent the results of these studies, based usually on few grams of sediment, are affected by spatial patchiness of deep-sea benthos. Here, we analyse the eDNA diversity of Foraminifera in 42 deep-sea sediment samples collected across different scales in the Southern Ocean. At three stations, we deployed at least twice the multicorer and from each multicorer cast, we subsampled 3 sediment replicates per core for 2 cores. Using high-throughput sequencing (HTS), we generated over 2.35 million high-quality sequences that we clustered into 451 operational taxonomic units (OTUs). The majority of OTUs were assigned to the monothalamous (single-chambered) taxa and environmental clades. On average, a one-gram sediment sample captures 57.9% of the overall OTU diversity found in a single core, while three replicates cover at most 61.9% of the diversity found in a station. The OTUs found in all the replicates of each core gather up to 87.9% of the total sequenced reads, but only represent from 12.2% to 30% of the OTUs found in one core. These OTUs represent the most abundant species, among which dominate environmental lineages. The majority of the OTUs are represented by few sequences comprising several well-known deep-sea morphospecies or remaining unassigned. It is crucial to study wider arrays of sample and PCR replicates as well as RNA together with DNA in order to overcome biases stemming from deep-sea patchiness and molecular methods.

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  • Environmental monitoring through protist next-generation sequencing metabarcoding: assessing the impact of fish farming on benthic foraminifera communities. Mol Ecol Resour 2014 Nov;14(6):1129-40. 10.1111/1755-0998.12261.

    abstract

    The measurement of species diversity represents a powerful tool for assessing the impacts of human activities on marine ecosystems. Traditionally, the impact of fish farming on the coastal environment is evaluated by monitoring the dynamics of macrobenthic infaunal populations. However, taxonomic sorting and morphology-based identification of the macrobenthos demand highly trained specialists and are extremely time-consuming and costly, making it unsuitable for large-scale biomonitoring efforts involving numerous samples. Here, we propose to alleviate this laborious task by developing protist metabarcoding tools based on next-generation sequencing (NGS) of environmental DNA and RNA extracted from sediment samples. In this study, we analysed the response of benthic foraminiferal communities to the variation of environmental gradients associated with salmon farms in Scotland. We investigated the foraminiferal diversity based on ribosomal minibarcode sequences generated by the Illumina NGS technology. We compared the molecular data with morphospecies counts and with environmental gradients, including distance to cages and redox used as a proxy for sediment oxygenation. Our study revealed high variations between foraminiferal communities collected in the vicinity of fish farms and at distant locations. We found evidence for species richness decrease in impacted sites, especially visible in the RNA data. We also detected some candidate bioindicator foraminiferal species. Based on this proof-of-concept study, we conclude that NGS metabarcoding using foraminifera and other protists has potential to become a new tool for surveying the impact of aquaculture and other industrial activities in the marine environment.

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  • Ancient DNA sheds new light on the Svalbard foraminiferal fossil record of the last millennium Geobiology, 12: 277–288. doi:10.1111/gbi.12087

    abstract

    Recent palaeogenetic studies have demonstrated the occurrence of preserved ancient DNA (aDNA) in various types of fossilised material. Environmental aDNA sequences assigned to modern species have been recovered from marine sediments dating to the Pleistocene. However, the match between the aDNA and the fossil record still needs to be evaluated for the environmental DNA approaches to be fully exploited. Here, we focus on foraminifera in sediments up to one thousand years old retrieved from the Hornsund fjord (Svalbard). We compared the diversity of foraminiferal microfossil assemblages with the diversity of aDNA sequenced from subsurface sediment samples using both cloning and high-throughput sequencing (HTS). Our study shows that 57% of the species archived in the fossil record were also detected in the aDNA data. However, the relative abundance of aDNA sequence reads and fossil specimens differed considerably. We also found a limited match between the stratigraphic occurrence of some fossil species and their aDNA sequences, especially in the case of rare taxa. The aDNA data comprised a high proportion of non-fossilised monothalamous species, which are known to dominate in modern foraminiferal communities of the Svalbard region. Our results confirm the relevance of HTS for studying past micro-eukaryotic diversity and provide insight into its ability to reflect fossil assemblages. Palaeogenetic studies including aDNA analyses of non-fossilised groups expand the range of palaeoceanographical proxies and therefore may increase the accuracy of palaeoenvironmental reconstructions.

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  • Ancient DNA complements microfossil record in deep-sea subsurface sediments. Biol. Lett. 2013 Aug;9(4):20130283. rsbl.2013.0283. 10.1098/rsbl.2013.0283. PMC3730641.

    abstract

    Deep-sea subsurface sediments are the most important archives of marine biodiversity. Until now, these archives were studied mainly using the microfossil record, disregarding large amounts of DNA accumulated on the deep-sea floor. Accessing ancient DNA (aDNA) molecules preserved down-core would offer unique insights into the history of marine biodiversity, including both fossilized and non-fossilized taxa. Here, we recover aDNA of eukaryotic origin across four cores collected at abyssal depths in the South Atlantic, in up to 32.5 thousand-year-old sediment layers. Our study focuses on Foraminifera and Radiolaria, two major groups of marine microfossils also comprising diverse non-fossilized taxa. We describe their assemblages in down-core sediment layers applying both micropalaeontological and environmental DNA sequencing approaches. Short fragments of the foraminiferal and radiolarian small subunit rRNA gene recovered from sedimentary DNA extracts provide evidence that eukaryotic aDNA is preserved in deep-sea sediments encompassing the last glacial maximum. Most aDNA were assigned to non-fossilized taxa that also dominate in molecular studies of modern environments. Our study reveals the potential of aDNA to better document the evolution of past marine ecosystems and opens new horizons for the development of deep-sea palaeogenomics.

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  • Ultra-deep sequencing of foraminiferal microbarcodes unveils hidden richness of early monothalamous lineages in deep-sea sediments. Proc. Natl. Acad. Sci. U.S.A. 2011 Aug;108(32):13177-82. 1018426108. 10.1073/pnas.1018426108. PMC3156150.

    abstract

    Deep-sea floors represent one of the largest and most complex ecosystems on Earth but remain essentially unexplored. The vastness and remoteness of this ecosystem make deep-sea sampling difficult, hampering traditional taxonomic observations and diversity assessment. This problem is particularly true in the case of the deep-sea meiofauna, which largely comprises small-sized, fragile, and difficult-to-identify metazoans and protists. Here, we introduce an ultra-deep sequencing-based metagenetic approach to examine the richness of benthic foraminifera, a principal component of deep-sea meiofauna. We used Illumina sequencing technology to assess foraminiferal richness in 31 unsieved deep-sea sediment samples from five distinct oceanic regions. We sequenced an extremely short fragment (36 bases) of the small subunit ribosomal DNA hypervariable region 37f, which has been shown to accurately distinguish foraminiferal species. In total, we obtained 495,978 unique sequences that were grouped into 1,643 operational taxonomic units, of which about half (841) could be reliably assigned to foraminifera. The vast majority of the operational taxonomic units (nearly 90%) were either assigned to early (ancient) lineages of soft-walled, single-chambered (monothalamous) foraminifera or remained undetermined and yet possibly belong to unknown early lineages. Contrasting with the classical view of multichambered taxa dominating foraminiferal assemblages, our work reflects an unexpected diversity of monothalamous lineages that are as yet unknown using conventional micropaleontological observations. Although we can only speculate about their morphology, the immense richness of deep-sea phylotypes revealed by this study suggests that ultra-deep sequencing can improve understanding of deep-sea benthic diversity considered until now as unknowable based on a traditional taxonomic approach.

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