Nematode communities along a bathymetric transect in the deep eastern Fram Strait (Arctic Ocean): interrelations between diversity, function and environment

As an expansion of a time-series study on meiobenthos in the Arctic deep sea, the diversity of free-living nematode communities along nine stations along a bathymetric transect was investigated morphologically in taxonomic and functional regards (feeding-type composition, life-history traits, tail-shape composition) and compared with previous studies of the same transect to investigate possible changes in the nematode community composition. Special emphasis was given on the analysis of sedimentary environmental parameters, which are used as proxies for food availability and sediment porosity. Multivariate statistics performed on nematode abundance data revealed a bathymetric zonation into four bathymetric zones: upper bathyal (1300 – 2000 m), lower bathyal (2500 - 3500 m), abyssal (5100 – 5600 m) and an additional ‘outgroup’ consisting of two stations with low nematode densities. Nematode densities generally decreased with increasing depth. Taxonomic diversity (EG(50), H’(log2), J’) decreased in a unimodal pattern peaking in the lower bathyal zone. A distance-based linear model revealed that 44% of the total variation in nematode abundances could be explained by the measured environmental parameters. Microbial feeders are the dominant feeding type along the transect with increasing dominance in the abyssal zone. The maturity index, a measure of environmental disturbance, decreased with depth, indicating a more colonizer-dominated community in the abyssal zone. Nematodes with long conico-cylindrical tails also become more dominant in the abyssal zone. A previous study of the same transect conducted in 2005 found a similar bathymetric zonation, but with a strikingly different dominant feeding type, i.e. epistrate feeders. Between the 2005 study and the year 2010 we conducted our study, the composition of the plankton community in the Fram Strait changed significantly due to a warm water anomaly in the region. We argue that through bentho-pelagic coupling, effects of this warm water anomaly on plankton communities could be a reason for the drastic change in dominant nematode feeding types

Advances in Taxonomy, Ecology, and Biogeography of Dirivultidae (Copepoda) Associated with Chemosynthetic Environments in the Deep Sea

Background: Copepoda is one of the most prominent higher taxa with almost 80 described species at deep-sea hydrothermal vents. The unique copepod family Dirivultidae with currently 50 described species is the most species rich invertebrate family at hydrothermal vents. Methodology/Principal Findings: We reviewed the literature of Dirivultidae and provide a complete key to species, and map geographical and habitat specific distribution. In addition we discuss the ecology and origin of this family. Conclusions/Significance: Dirivultidae are only present at deep-sea hydrothermal vents and along the axial summit trough of midocean ridges, with the exception of Dirivultus dentaneus found associated with Lamellibrachia species at 1125 m depth off southern California. To our current knowledge Dirivultidae are unknown from shallow-water vents, seeps, whale falls, and wood falls. They are a prominent part of all communities at vents and in certain habitat types (like sulfide chimneys colonized by pompei worms) they are the most abundant animals. They are free-living on hard substrate, mostly found in aggregations of various foundation species (e. g. alvinellids, vestimentiferans, and bivalves). Most dirivultid species colonize more than one habitat type. Dirivultids have a world-wide distribution, but most genera and species are endemic to a single biogeographic region. Their origin is unclear yet, but immigration from other deep-sea chemosynthetic habitats (stepping stone hypothesis) or from the deep-sea sediments seems unlikely, since Dirivultidae are unknown from these environments. Dirivultidae is the most species rich family and thus can be considered the most successful taxon at deep-sea vents

Detailed Mapping of Hydrothermal Vent Fauna: A 3D Reconstruction Approach Based on Video Imagery

Active hydrothermal vent fields are complex, small-scale habitats hosting endemic fauna that changes at scales of centimeters, influenced by topographical variables. In previous studies, it has been shown that the distance to hydrothermal fluids is also a major structuring factor. Imagery analysis based on two dimensional photo stitching revealed insights to the vent field zonation around fluid exits and a basic knowledge of faunal assemblages within hydrothermal vent fields. However, complex three dimensional surfaces could not be adequately replicated in those studies, and the assemblage structure, as well as their relation to abiotic terrain variables, is often only descriptive. In this study we use ROV video imagery of a hydrothermal vent field on the southeastern Indian Ridge in the Indian Ocean. Structure from Motion photogrammetry was applied to build a high resolution 3D reconstruction model of one side of a newly discovered active hydrothermal chimney complex, allowing for the quantification of abundances. Likewise, the reconstruction was used to infer terrain variables at a scale important for megabenthic specimens, which were related to the abundances of the faunal assemblages. Based on the terrain variables, applied random forest model predicted the faunal assemblage distribution with an accuracy of 84.97 %. The most important structuring variables were the distances to diffuse- and black fluid exits, as well as the height of the chimney complex. This novel approach enabled us to classify quantified abundances of megabenthic taxa to distinct faunal assemblages and relate terrain variables to their distribution. The successful prediction of faunal assemblage occurrences further supports the importance of abiotic terrain variables as key structuring factors in hydrothermal systems and offers the possibility to detect suitable areas for Marine Protected areas on larger spatial scales. This technique works for any kind of video imagery, regardless of its initial purpose and can be implemented in marine monitoring and management

A universal tool for marine metazoan species identification: towards best practices in proteomic fingerprinting

AbstractProteomic fingerprinting using MALDI-TOF mass spectrometry is a well-established tool for identifying microorganisms and has shown promising results for identification of animal species, particularly disease vectors and marine organisms. And thus can be a vital tool for biodiversity assessments in ecological studies. However, few studies have tested species identification across different orders and classes. In this study, we collected data from 1246 specimens and 198 species to test species identification in a diverse dataset. We also evaluated different specimen preparation and data processing approaches for machine learning and developed a workflow to optimize classification using random forest. Our results showed high success rates of over 90%, but we also found that the size of the reference library affects classification error. Additionally, we demonstrated the ability of the method to differentiate marine cryptic-species complexes and to distinguish sexes within species.</jats:p

Threatened by mining, polymetallic nodules are required to preserve abyssal epifauna

Polymetallic nodule mining at abyssal depths in the Clarion Clipperton Fracture Zone (Eastern Central Pacific) will impact one of the most remote and least known environments on Earth. Since vast areas are being targeted by concession holders for future mining, large-scale effects of these activities are expected. Hence, insight into the fauna associated with nodules is crucial to support effective environmental management. In this study video surveys were used to compare the epifauna from sites with contrasting nodule coverage in four license areas. Results showed that epifaunal densities are more than two times higher at dense nodule coverage (>25 versus ≤10 individuals per 100 m2), and that taxa such as alcyonacean and antipatharian corals are virtually absent from nodule-free areas. Furthermore, surveys conducted along tracks from trawling or experimental mining simulations up to 37 years old, suggest that the removal of epifauna is almost complete and that its full recovery is slow. By highlighting the importance of nodules for the epifaunal biodiversity of this abyssal area, we urge for cautious consideration of the criteria for determining future preservation zones

Natural variability of geochemical conditions, biogeochemical processes and element fluxes in sediments of the CCZ

During RV SONNE cruise SO239 in March/April 2015 five sites in the area of the Clarion-Clipperton Fracture Zone (CCZ) in the eastern equatorial Pacific were visited as part of the JPI Oceans pilot action Ecological Aspects of Deep-Sea Mining“. Here, we present a comparable study on (1) the redox zonation in the sediments induced by the input flux of organic matter, (2) biogeochemical reactions including the driver of organic matter degradation and (3) diagenetic manganese redistribution and implications for manganese nodule formation

Habitat heterogeneity enhances megafaunal biodiversity at bathymetric elevations in the Clarion Clipperton Fracture Zone

The Clarion Clipperton Fracture Zone (CCZ) in the northeast Pacific is a heterogeneous deep-sea environment, featuring abyssal plains as well as multiple seamounts and abyssal hills (bathymetric elevations) that harbour a highly diverse megabenthic fauna. Based on the analysis of seafloor photographic transects that were taken from elevated areas downslope into the abyssal plains in the eastern CCZ, a similar distribution of habitats was observed on five different bathymetric elevations including abyssal hills as well as the foothills of two seamounts. Rock outcrops occur at the summits, surrounded by an area with varying coverage and size of polymetallic nodules, which were divided into two different habitats characterized by large and small nodules, respectively, and followed by nodule-free sediments. Megafauna composition, density and diversity varies across these habitats. While density is the highest in areas with rock outcrops (1.4 individuals per m2), the biodiversity is the highest when regarding all of the habitats combined. Regarded individually, nodule-covered areas are the most diverse, whereas sediment areas without hard substratum, i.e. nodule free sediments, show the lowest biodiversity and the lowest density (0.2 individuals per m2). The multinomial species classification method (CLAM) shows that most of the observed megafauna morphotypes have to be regarded as rare. The large differences between the megafaunal communities at bathymetric elevations and the abyssal plain reported from previous studies might partly be explained by the multiplicity of habitats. This high heterogeneity can lead to a more diversified community at elevations, although most habitats can also be observed in the abyssal plain

Macrofaunal foraminifera from a former benthic impact experiment site (IOM contract area) in the abyssal eastern Clarion-Clipperton Zone

We analysed macrofaunal (>250 μm) foraminifera in the 0–1 cm layer of three replicate multicorer samples collected in 2015 at each of three abyssal sites (‘impacted’, ‘resedimented’ and ‘control’) in the IOM contract area of the eastern Clarion-Clipperton Zone (CCZ), where a benthic impact experiment (BIE) had been conducted in 1995 in order to simulate disturbances resulting from the seabed mining of polymetallic nodules. Taxonomic composition was similar between sites, with monothalamids representing 79% of complete ‘live’ (Rose-Bengal-stained) tests and multichambered taxa constituting a slim majority (55% overall) of dead tests. Monothalamids comprised a mixture of formal taxa and informal morphological groupings. Komokiaceans in the family Baculellidae predominated and included the top-ranked species Edgertonia sp. 7. Other komokiaceans (Komokiidae) and tubular, spindle-shaped and spherical morphotypes were also common. Multichambered taxa were mainly agglutinated, uniserial hormosinids being well represented together with coiled species, notably Cribrostomoides subglobosus (2nd ranked species). Fragments were almost three times as abundant as complete tests and dominated by tubes (notably Rhizammina sp.), many of them ‘live’. Our results are consistent with earlier studies showing that monothalamids, many of them undescribed, are important elements of abyssal foraminiferal assemblages in the eastern CCZ. Mean specimen counts for ‘live’ and dead tests (50.7–75.7 and 54.3–72.7 individuals/sample, respectively) were not significantly different between sites. Assemblages were very diverse with 43–85 morphospecies per sample and 220 in total (201–1081 specimens per sample, 4361 total), more than three-quarters of them monothalamids. Species richness and diversity were lower at the control site than at the impacted and resedimented sites, and eveness and Rank 1 dominance lowest at the resedimented site, but differences were not significant for any of these metrics. The absence of significant differences in faunal density, diversity, and taxonomic composition at impacted, resedimented and control sites 20 years after the experimental disturbance may reflect a number of factors, including insufficient sample replication