Novel benthic foraminifera are abundant and diverse in an area of the abyssal equatorial Pacific licensed for polymetallic nodule exploration

The benthic biota of the Clarion–Clipperton Zone (CCZ, abyssal eastern equatorial Pacific) is the focus of a major research effort linked to possible future mining of polymetallic nodules. Within the framework of ABYSSLINE, a biological baseline study conducted on behalf of Seabed Resources Development Ltd. in the UK-1 exploration contract area (eastern CCZ, ~4,080 m water depth), we analysed foraminifera (testate protists), including ‘live’ (Rose Bengal stained) and dead tests, in 5 cores (0–1 cm layer, >150-μm fraction) recovered during separate megacorer deployments inside a 30 by 30 km seafloor area. In both categories (live and dead) we distinguished between complete and fragmented specimens. The outstanding feature of these assemblages is the overwhelming predominance of monothalamids, a group often ignored in foraminiferal studies. These single-chambered foraminifera, which include agglutinated tubes, spheres and komokiaceans, represented 79% of 3,607 complete tests, 98% of 1,798 fragments and 76% of the 416 morphospecies (live and dead combined) in our samples. Only 3.1% of monothalamid species and 9.8% of all species in the UK-1 assemblages are scientifically described and many are rare (29% singletons). Our results emphasise how little is known about foraminifera in abyssal areas that may experience major impacts from future mining activities

Loricifera inhabiting spherical agglutinated structures in the abyssal eastern equatorial Pacific nodule fields

Loriciferans are known to survive in extreme environments, most notably in the case of a recently described Spinoloricus species from a hypersaline anoxic Mediterranean basin. Our new discovery of members of the genus Rugiloricus inside spherical agglutinated structures from sediment samples collected in the manganese nodules fields of the eastern Clarion-Clipperton Zone (CCZ, abyssal equatorial Pacific) demonstrates that these tiny animals are able to spring fresh surprises. Nearly all developmental stages of an undescribed Rugiloricus species were found inside the spheres, from the first instar larva and large free larva to the two stages of the postlarva inside the larval exuvium. Only the adults were missing. The spheres themselves were almost certainly not created by the loriciferans. Their origin is unclear, although similar agglutinated structures from the same study area contain cells that resemble monothalamous foraminifera, suggesting that they are possibly made by foraminifera. One of our CCZ samples also yielded a single free specimen of the loriciferan genus Pliciloricus that was not hidden inside an agglutinated structure. This specimen is particularly interesting because, like nested Russian dolls, it has all stages inside the larval exuvium: first the larval exuvium itself with the two toes, then a very thin postlarval exuvium and finally the adult male with two testes filled with mature spermatozoa

Diversity and spatial patterns of foraminiferal assemblages in the eastern Clarion–Clipperton zone (abyssal eastern equatorial Pacific)

Foraminifera are a major component of the abyssal meiofauna in parts of the eastern Pacific Clarion-Clipperton Zone (CCZ) designated by the International Seabed Authority for polymetallic nodule exploration. We analysed the diversity and distribution of stained (‘live’) and unstained (dead) assemblages (0–1 cm layer, >150-μm sieve fraction) in megacorer samples from 11 sites (water depths 4051–4235 m) within three 30 × 30 km ‘strata’ in the United Kingdom 1 (UK1 Strata A and B; 5 and 3 samples, respectively) and Ocean Minerals Singapore (3 samples) exploration contract areas and separated by distances of up to 28 km within a stratum and 224 km between strata. Foraminiferal assemblage density, diversity and composition at the higher taxon/morphogroup level were largely consistent between samples. Stained assemblages were dominated (>86%) by single-chambered monothalamids, mainly spheres, tubes, komokiaceans and forms that are difficult to categorise morphologically. Hormosinaceans were the most common multichambered group (∼10%), while calcareous taxa (mainly rotaliids) represented only ∼3.5% of stained tests. Dead foraminifera were more evenly distributed between monothalamids (56%) and multichambered taxa (44%). Almost all test fragments were monothalamids, mainly tubes. Morphospecies were added regularly with each new sample and totalled 580 (stained + dead, complete + fragments), of which 159 occurred in all three strata, 222 were shared between UK1 Strata A and B, 209 between UK1A and the OMS Stratum, and 193 between UK1B and the OMS Stratum. Individual strata yielded 310–411 and individual samples 132–228 putative morphospecies. The majority (550) of the 580 species were represented by intact tests of which 462 included at least some that were stained. Most of the stained (∼80%) and stained + dead (∼75%) species were monothalamids, almost all of them undescribed. Many species were rare; 146 of the 550 species with complete tests (stained + dead) were singletons and 53 doubletons. Values of Morisita's index indicated that most individual species represented by ≥ 10 complete tests had aggregated distributions. In MDS plots, all 11 samples fell within the 95% confidence limit, consistent with a general uniformity in assemblage composition. However, there was also a weak grouping of UK1A samples, while a plot of Bray-Curtis similarity against distance between samples suggests that there may be some gradual change in assemblage composition related to distance. We conclude that the foraminiferal assemblages at our eastern CCZ sites are highly diverse, dominated by undescribed monothalamids, include many rare species, and are fairly similar across the study area, but with a patchy distribution at the level of individual morphospecies

The Contribution of fine sieve fractions (63–150 μm) to foraminiferal abundance and diversity in an area of the Eastern Pacific Ocean licensed for polymetallic nodule Exploration

The sieve mesh sizes used in benthic foraminiferal studies exert a strong influence on faunal densities and composition. We examined the consequences of including finer (63–150 μm) size classes in a study of Rose Bengal stained (‘live’) and dead foraminifera in 5 Megacorer samples (0–1 cm layer) from abyssal sites in the eastern Clarion-Clipperton Zone (CCZ; equatorial Pacific), a region with commercially significant deposits of polymetallic nodules. More than 60% of intact specimens originated from the finer (90%) to the finer fractions; the corresponding number for the stained + dead assemblage was 12 out of 35. Of the 46 most abundant species in the stained + dead assemblage, 35 were monothalamids (mainly spheres, Lagenammina spp., Nodellum-like forms, and saccamminids), the remainder being rotaliids (3), hormosinids (3), trochamminids (3) and textulariids (2). By far the most abundant species overall, a tiny agglutinated sphere, was almost entirely confined to the finer fractions. Although small foraminifera that pass through a 150-μm screen are time-consuming to analyze, they constitute an important part of abyssal Pacific assemblages and may include opportunistic species that respond to episodic food pulses as well as pioneer recolonizers of defaunated substrates. It is therefore important to consider them in studies of possible mining impacts on abyssal benthic communities

Giant protists (xenophyophores, Foraminifera) are exceptionally diverse in parts of the abyssal eastern Pacific licensed for polymetallic nodule exploration

Xenophyophores, giant, fragile, agglutinated foraminifera (protists), are major constituents of the abyssal megafauna in the equatorial Pacific Clarion-Clipperton Zone (CCZ), a region where seabed mining of polymetallic nodules may occur in the future. As part of a baseline study of benthic communities we made extensive collections of xenophyophores in two areas (UK-1 and OMS) licensed for exploration by the International Seabed Authority. Based on test morphology, we distinguished 36 morphospecies (34 new to science) among 130 specimens. Twenty of these morphospecies yielded 184 DNA sequences, a 14-fold increase in genetic data for xenophyophores that confirms their high diversity in the eastern CCZ. A further 15 morphospecies (8 new to science) were recognised in samples from two other areas (APEI-6 and Russian exploration license area) within or adjacent to the CCZ. This large number of species confirms that the CCZ is a focal area for xenophyophore diversity. More broadly, it represents an unprecedented increase in the known global diversity of xenophyophores and suggests that many species remain undiscovered in the World's oceans. Xenophyophores are often sessile on nodules in the CCZ, making these delicate organisms particularly vulnerable to mining impacts. They can also play a crucial role in deep-sea ecosystems, providing habitat structures for meiofaunal and macrofaunal organisms and enhancing the organic content of sediments surrounding their tests. The loss of xenophyophores due to seabed mining may therefore have wider implications for the recovery of benthic communities following major human disturbances on the abyssal seafloor

Five new species and two new genera of xenophyophores (Foraminifera: Rhizaria) from part of the abyssal equatorial Pacific licensed for polymetallic nodule exploration

Based on a combination of morphological and molecular data, we describe five new species and two new genera of xenophyophores from the Clarion–Clipperton Zone (abyssal eastern Pacific), an area with commercially valuable seafloor deposits of polymetallic nodules. Bizarria bryiformis gen. et sp. nov. displays unusual features, notably an organic-walled test, largely devoid of agglutinated particles, comprising interconnected branches growing upwards from the nodule substrate; the bases of the branches contain dark masses of waste material (stercomare) and pale strands of cytoplasm (granellare), the whitish, tuft-like extremities contain sediment particles. Tendalia reteformis gen. et sp. nov. forms a delicate network of agglutinated tubes. Shinkaiya contorta sp. nov. is characterized by a contorted, partly reticulated plate-like test while the simpler plate-like test of Galatheammina interstincta sp. nov. combines characters typical of Galatheammina and Psammina. In Semipsammina mattaeformis sp. nov., a thin, delicate test with one or more tubular extensions forms a flat canopy over the mat-like stercomare encrusting the nodule substrate. Tendalia reteformis and S. contorta are free-living; the other species are sessile on nodules. Together, they illustrate the considerable morphological diversity of xenophyophores in a region where they dominate the megafauna, and highlight some major taxonomic challenges posed by these giant monothalamous foraminifera

Xenophyophores (Rhizaria, Foraminifera) from the Eastern Clarion-Clipperton Zone (equatorial Pacific): the Genus Psammina

Xenophyophores are important megafaunal organisms in the abyssal Clarion-Clipperton Zone (CCZ; equatorial Pacific), a region hosting commercially significant deposits of polymetallic nodules. Previous studies assigned those with attached, fan-like tests to Psammina limbata, a species described from the central CCZ based on morphology. Here, we redescribe the holotype of P. limbata and then show that limbata-like morphotypes collected in the eastern CCZ include three genetically distinct species. Psammina aff. limbata is closest morphologically to P. limbata. The others are described as P. microgranulata sp. nov. and P. rotunda sp. nov. These fan-shaped species form a well-supported clade with P. tortilis sp. nov., a morphologically variable species exhibiting features typical of both Psammina and Semipsammina. A second clade containing Psammina sp. 3, and two species questionably assigned to Galatheammina branches at the base of this group. The genus Psammina includes another 9 described species for which there are no genetic data, leaving open the question of whether Psammina as a whole is monophyletic. Our study increases the number of xenophyophore species described from the eastern CCZ from 8 to 11, with a further 25 morphotypes currently undescribed. Many additional species of these giant foraminifera undoubtedly await discovery in abyssal settings

Characteristics of meiofauna in extreme marine ecosystems: a review

Extreme marine environments cover more than 50% of the Earth’s surface and offer many opportunities for investigating the biological responses and adaptations of organisms to stressful life conditions. Extreme marine environments are sometimes associated with ephemeral and unstable ecosystems, but can host abundant, often endemic and well-adapted meiofaunal species. In this review, we present an integrated view of the biodiversity, ecology and physiological responses of marine meiofauna inhabiting several extreme marine environments (mangroves, submarine caves, Polar ecosystems, hypersaline areas, hypoxic/anoxic environments, hydrothermal vents, cold seeps, carcasses/sunken woods, deep-sea canyons, deep hypersaline anoxic basins [DHABs] and hadal zones). Foraminiferans, nematodes and copepods are abundant in almost all of these habitats and are dominant in deep-sea ecosystems. The presence and dominance of some other taxa that are normally less common may be typical of certain extreme conditions. Kinorhynchs are particularly well adapted to cold seeps and other environments that experience drastic changes in salinity, rotifers are well represented in polar ecosystems and loriciferans seem to be the only metazoan able to survive multiple stressors in DHABs. As well as natural processes, human activities may generate stressful conditions, including deoxygenation, acidification and rises in temperature. The behaviour and physiology of different meiofaunal taxa, such as some foraminiferans, nematode and copepod species, can provide vital information on how organisms may respond to these challenges and can provide a warning signal of anthropogenic impacts. From an evolutionary perspective, the discovery of new meiofauna taxa from extreme environments very often sheds light on phylogenetic relationships, while understanding how meiofaunal organisms are able to survive or even flourish in these conditions can explain evolutionary pathways. Finally, there are multiple potential economic benefits to be gained from ecological, biological, physiological and evolutionary studies of meiofauna in extreme environments. Despite all the advantages offered by meiofauna studies from extreme environments, there is still an urgent need to foster meiofauna research in terms of composition, ecology, biology and physiology focusing on extreme environments

ECOLOGIE DES FORAMINIFERES BENTHIQUES DANS LE PRODELTA DU RHONE DETERMINATION DE BIO-INDICATEURS ENVIRONNEMENTAUX ET RECONSTITUTION HISTORIQUE D'UNE ANTHROPISATION RECENTE

This thesis was realised in the context of the French research projects CHACCRA (Climate and Humaninduced AIterations in Carbon Cycling at the River-seA connection) and EXTREMA (Episodes météo-climatiques. extrêmes et redistribution des masses sédimentaires et des polluants associés au sein d'un système côtier). The aim of this work is to precise the ecology of benthic foraminiferal faunas on the continental shelf under the influence of the Rhône River (Gulf of Lions, NW Mediterranean). The final purpose is to use benthic foraminifera as bio-, indicators of present and past environmental conditions prevailing in the Rhône prodelta. Physico-chemical parameters controlling the structure (standing stocks, faunal composition), the spatial variability and temporal dynamics of the living faunas were identified. Hydro-sedimentary disturbance related to major Rhône River flood events appears to be an important ecological constrain for the faunas living close to the river mouth. The quality and the quantity of available organic matter in the sediment are also key parameters controlling the temporal and spatial dynamics of foraminiferal communities. Thereafter, we have defined a tool (i.e., proxy) based on fossil benthic foraminiferal assemblages. It permitted us to reconstruct the recent evofution of the Rhône prodelta for the last 400 years in terms of sedimentary and organic fluxes.Cette thèse a été réalisée dans le cadre de 2 projets ANR (Vulnérabilité : Milieux et Climats) : le projet CHACCRA (Climate and Human-induced Alterations in Carbon Cycling at the River-seA connection) et le projet EXTREMA (Episodes météo-climatiques extrêmes et redistribution des masses sédimentaires et des polluants associés au sein d'un système côtier). L'objectif de ce travail doctoral a été de définir les caractéristiques écologiques des faunes de foraminifères benthiques vivant sur la plate-forme continentale dans la zone d'influence du Rhône (Golfe du Lion, Nord-ouest de la Mer Méditerranée), afin d'utiliser les faunes benthiques en tant que bioindicateurs des caractéristiques environnementales actuelles et passées. Aussi, les facteurs environnementaux contraignant la structure (densité, composition faunistique) ainsi que la distribution spatiale et la variabilité temporelle des faunes actuelles de foraminifères benthiques ont été identifiés. Il a été mis en évidence Ie rôle des apports épisodiques de sédiments lors des crues du Rhône, constituant un facteur de stress pour les faunes benthiques vivant près de l'embouchure. La nature et la quantité de matière organique détritique ainsi que les processus liés à la dégradation de cette matière sont également apparus comme des contraintes écologiques majeures contrôlant la dynamique spatiale et temporelle des communautés. Par la suite, un outil basé sur les assemblages fossiles de foraminifères benthiques préservés dans les sédiments au débouché du fleuve a été défini. Celui-ci a permis de retracer l'histoire récente (400 dernières années) du prodelta du Rhône en termes d'apports fluviatiles terrigènes et organiques