Radiolarian tests as microhabitats for novel benthic foraminifera: observations from the abyssal eastern equatorial Pacific (Clarion–Clipperton fracture zone)

We investigated benthic foraminifera inhabiting the empty tests of radiolarians in surface sediment samples from the abyssal Clarion–Clipperton Fracture Zone (13°50’N, 116°35’W; ~4080 m water depth), eastern equatorial Pacific, an area licensed for the future mining of polymetallic nodules. Based on two megacore samples (>150 µm, 0–1 cm sediment layer; 78.6 cm2 surface area), we examined 288 radiolarian tests that were occupied by ‘live’ (stained) inhabitants presumed to be foraminifera based on test morphology and wall structure; these quantitative data were supplemented by qualitative records from three additional cores. The radiolarian inhabitants comprised organic-walled and agglutinated monothalamous (single-chambered) and less common polythalamous (multichambered) forms. Among the 27 distinctive morphotypes, a few can be assigned to a described superfamily (Komokiacea) or to genera such as Lagenammina, Thurammina and Hormosinella, while two brown, organic-walled multichambered forms resemble the genera Hospitella and Placopsilinella. The remainder were assigned to informal morphotypes. The radiolarian inhabitants are generally small (9% of the total ‘live’ (stained) foraminiferal assemblage, thereby making non-negligible contribution to local species diversity and foraminiferal abundance in our study area. Our new observations, and previous studies of benthic foraminifera inhabiting the empty shells of other foraminifera, suggest that high biodiversity among meiofaunal-sized deep-sea organisms (particularly foraminifera) is enhanced by the colonisation of small cryptic microhabitats. Based on their complex test morphology, we suggest that at least some of the diverse monothalamous foraminifera that typically dominate abyssal foraminiferal assemblages have little or no mobility, making them well suited to this mode of life

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

Formation of agglutinated cysts by the foraminiferan Sphaeroidina bulloides on the Porcupine Abyssal Plain (NE Atlantic)

Benthic foraminiferal species sometimes produce a covering made of sediment and detrital material around their tests (shells). These sedimentary envelopes, termed ‘cysts’, have been observed in a number of species, from organic-walled and agglutinated to calcareous (e.g., Linke and Lutze 1993; Cedhagen 1996; Gross 2000, 2002; Gooday and Hughes 2002; Heinz et al. 2005). However, almost all published records of this phenomenon originate from coastal or bathyal settings, and there are very few examples from abyssal depths, i.e. deeper than 3500 m. During the analysis of Megacorer samples (25.5 cm2 surface area, formalin-buffered, 0–1 cm sediment horizon, >150 ?m fraction) collected in the area of the Porcupine Abyssal Plain Sustained Observatory (PAP-SO) in the northeast Atlantic (49°N 16.5°W, 4850 m water depth), we observed benthic foraminifera that had created partial or complete muddy coatings. Most belonged to Sphaeroidina bulloides d’Orbigny, 1826 (Fig. 1), and a few to Melonis barleeanus (Williamson, 1858). The S. bulloides cysts occasionally incorporated juvenile planktonic foraminiferal tests (<50 ?m), and always included one or more flexible agglutinated tubes (20–35 ?m wide, 140–400 ?m long) that extended out of the main structure (Fig. 1a–e). There was no evidence of the presence within the cysts of microscopic organisms, comparable to the ciliates and nematodes observed by Linke and Lutze (1993) inside the cysts of Elphidium incertum

Unique benthic foraminiferal communities (stained) in diverse environments of sub-Antarctic fjords, South Georgia

Sub-Antarctic fjords are among the environments most affected by the recent climate change. In our dynamically changing world, it is essential to monitor changes in these vulnerable settings. Here, we present a baseline study of “living” (rose-bengal-stained) benthic foraminifera from fjords of South Georgia, including fjords with and without tidewater glaciers. Their distribution is analyzed in the light of new fjord water and sediment property data, including grain size and sorting, total organic carbon, total sulfur, and δ13C of bulk organic matter. Four well-defined foraminiferal assemblages are recognized. Miliammina earlandi dominates in the most restricted, near-shore and glacier-proximal habitats, Cassidulinoides aff. parkerianus in mid-fjord areas, and Globocassidulina aff. rossensis and an assemblage dominated by Ammobaculites rostratus, Reophax subfusiformis, and Astrononion echolsi are in the outer parts of the fjords. Miliammina earlandi can tolerate strong glacial influence, including high sedimentation rates in fjord heads and sediment anoxia, as inferred from sediment color and total organic carbon  sulfur ratios. This versatile species thrives both in the food-poor inner reaches of fjords that receive mainly refractory petrogenic organic matter from glacial meltwater and in shallow-water coves, where it benefits from an abundant supply of fresh, terrestrial, and marine organic matter. A smooth-walled variant of C. aff. parkerianus, apparently endemic to South Georgia, is the calcareous rotaliid best adapted to inner-fjord conditions characterized by moderate glacial influence and sedimentation rates and showing no preference for particular sedimentary redox conditions. The outer parts of fjords with clear, well-oxygenated bottom water are inhabited by G. aff. rossensis. Ammobaculites rostratus, R. subfusiformis, and A. echolsi dominate in the deepest-water settings, with water salinities ≥ 33.9 PSU and temperatures 0.2–1.4 ∘C, characteristic of winter water and Upper Circumpolar Deep Water. The inner- and mid-fjord foraminiferal assemblages seem specific to South Georgia, although with continued warming and deglaciation, they may become more widespread in the Southern Ocean.Polish National Science Centre (grant no. 2018/31/B/ST10/02886

A new genus and two new species of saccamminid foraminiferans (Protista, Rhizaria) from the deep Southern Ocean

FIGURE 3. Leptammina flavofusca gen. et sp. nov. Assemblage of individuals from Stn. 102 # 13 EBS. A. Fresh, newly collected, and probably alive individuals. B. The same individuals after fixation in formalin. Scale bars = 1 mm

Abyssal hills: influence of topography on benthic foraminiferal assemblages

Abyssal plains, often thought of as vast flat areas, encompass a variety of terrains including abyssal hills, features that constitute the single largest landscape type on Earth. The potential influence on deep-sea benthic faunas of mesoscale habitat complexity arising from the presence of abyssal hills is still poorly understood. To address this issue we focus on benthic foraminifera (testate protists) in the >150-?m fraction of Megacorer samples (0–1 cm layer) collected at five different sites in the area of the Porcupine Abyssal Plain Sustained Observatory (NE Atlantic, 4850 m water depth). Three sites are located on the tops of small abyssal hills (200–500 m elevation) and two on the adjacent abyssal plain. We examined benthic foraminiferal assemblage characteristics (standing stock, diversity, composition) in relation to seafloor topography (hills vs. plain). Density and rarefied diversity were not significantly different between the hills and the plain. Nevertheless, hills do support a higher species density (i.e. species per unit area), a distinct fauna, and act to increase the regional species pool. Topographically enhanced bottom-water flows that influence food availability and sediment type are suggested as the most likely mechanisms responsible for these differences. Our findings highlight the potential importance of mesoscale heterogeneity introduced by relatively modest topography in regulating abyssal foraminiferal diversity. Given the predominance of abyssal hill terrain in the global ocean, we suggest the need to include faunal data from abyssal hills in assessments of abyssal ecology

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

Taxonomic composition and distribution of soft-walled monothalamid foraminifera in the area of Zernov’s Phyllophora Field (NW Black Sea)

We studied assemblages of soft-walled, single-chambered foraminifera (monothalamids) at eight stations in the area of Zernov's Phyllophora Field (ZPF) on the NW continental shelf of the Black Sea. This work is based on samples collected during Cruise 70 of the RV Professor Vodyanitsky and provides the first analysis of the taxonomic composition of monothalamids from this region. These delicate, poorly known foraminifera were found at all stations in the studied area. They were represented by nine forms that are identified to species or genus level as well as 14 undescribed species, nine of which are found in the Black Sea for the first time. Four species, Psammophaga sp., Vellaria pellucida, Goodayia rostellata and Krymia fusiformis, were most abundant, with Psammophaga sp. being the dominant species overall. Previous studies have suggested a link between members of this genus and eutrophication. There are a number of taxonomic parallels between these ZPF assemblages and those from the Adriatic Sea, e.g. the occurrence of the genera Goodayia, Psammophaga and Vellaria, although it is possible that some other taxa are endemic to the Black Sea