Deep-sea Assemblages Research Articles

Numbers of fish species, higher taxa, and phylogenetic similarity decrease with latitude and depth, and deep-sea assemblages are unique.

Species richness has been found to increase from the poles to the tropics but with a small dip near the equator over all marine fishes. Phylogenetic diversity measures offer an alternative perspective on biodiversity linked to evolutionary history. If phylogenetic diversity is standardized for species richness, then it may indicate places with relatively high genetic diversity. Latitudes and depths with both high species and phylogenetic diversity would be a priority for conservation. We compared latitudinal and depth gradients of species richness, and three measures of phylogenetic diversity, namely average phylogenetic diversity (AvPD), the sum of the higher taxonomic levels (STL) and the sum of the higher taxonomic levels divided by the number of species (STL/spp) for modelled ranges of 5,619 marine fish species. We distinguished all, bony and cartilaginous fish groups and four depth zones namely: whole water column; 0 -200 m; 201-1,000 m; and 1,001-6,000 m; at 5° latitudinal intervals from 75°S to 75°N, and at 100 m depth intervals from 0 m to 3,500 m. Species richness and higher taxonomic richness (STL) were higher in the tropics and subtropics with a small dip at the equator, and were significantly correlated among fish groups and depth zones. Species assemblages had closer phylogenetic relationships (lower AvPD and STL/spp) in warmer (low latitudes and shallow water) than colder environments (high latitudes and deep sea). This supports the hypothesis that warmer shallow latitudes and depths have had higher rates of evolution across a range of higher taxa. We also found distinct assemblages of species in different depth zones such that deeper sea species are not simply a subset of shallow assemblages. Thus, conservation needs to be representative of all latitudes and depth zones to encompass global biodiversity.

Detection of community-wide impacts of bottom trawl fishing on deep-sea assemblages using environmental DNA metabarcoding.

Although considerable research progress on the effects of anthropogenic disturbance in the deep sea has been made in recent years, our understanding of these impacts at community level remains limited. Here, we studied deep-sea assemblages of Sicily (Mediterranean Sea) subject to different intensities of benthic trawling using environmental DNA (eDNA) metabarcoding and taxonomic identification of meiofauna communities. Firstly, eDNA metabarcoding data did not detect trawling impacts using alpha diversity whereas meiofauna data detected a significant effect of trawling. Secondly, both eDNA and meiofauna data detected significantly different communities across distinct levels of trawling intensity when we examined beta diversity. Taxonomic assignment of the eDNA data revealed that Bryozoa was present only at untrawled sites, highlighting their vulnerability to trawling. Our results provide evidence for community-wide impacts of trawling, with different trawling intensities leading to distinct deep-sea communities. Finally, we highlight the need for further studies to unravel understudied deep-sea biodiversity.

Macrobenthic diversity response to the atlantification of the Arctic Ocean (Fram Strait, 79°N) – A taxonomic and functional trait approach

This is the first study presenting temporal changes of the macrofauna biodiversity along the bathymetric gradient from the shelf to abyssal depths in the eastern Fram Striat. In this region, between 2004 and 2008, a significant increase in surface water temperature was observed due to the transport of Atlantic water from lower latitudes and was defined as a Warm Water Anomaly (WWA). Effects of the WWA in the eastern Fram Strait were observed across the entire food web, from the pelagic to the deep seafloor. The material for our study was collected before (in 2000) and after the WWA (in 2010 and 2017) at station depths ranging from 203 m to 5561 m. Samples of macrofauna and surface sediments were collected with use of a box corer to analyze species composition and functional traits, and environmental characteristics in sediments. We explore the influence of environmental changes on the structure (species composition and diversity) and functioning (functional trait composition and diversity) of macrofauna communities. An increase of primary production in surface waters during and after the WWA was reflected in a higher food availability at the seafloor from shelf to abyssal depths. Warming induced environmental changes led to an increase of macrofauna density and taxonomic diversity at all water depths. Macrofauna species composition significantly changed after the WWA. At all study sites, macrofauna functional diversity increased after the warm period. Functional trait composition changed significantly along the bathymetric transect. Despite changes in the taxonomic composition, macrofauna communities at the shallowest stations showed high functional redundancy, i.e., trait composition remained unchanged after the WWA. At water depths below 1500 m, where functional redundancy was significantly lower, functional trait composition changed significantly after the WWA. Our results suggest that macrofauna communities on the shelves are more resistant to environmental changes compared to deep-sea assemblages in the eastern Fram Strait.

A deep-sea foraminiferal assemblage scattered through the late Cenozoic of Antarctic Peninsula and its biostratigraphic and biogeographic implications

AbstractOur knowledge of the foraminiferal fossil record of Antarctica is notoriously patchy but still offers us an overview of its Cenozoic faunas. Few occurrences have been reported for the continent, with deep-sea assemblages described mainly for its eastern portion. Here we describe 21 taxa of large agglutinated foraminifers from the Miocene Hobbs Glacier Formation and the Plio-Pleistocene Weddell Sea Formation on Seymour Island, West Antarctica, including the gigantic Ammodiscus vastus new species. Most of them consist of genera or species typical of deep-sea agglutinated assemblages. All specimens are completely filled and partially covered by lithified micrite. This, along with the postfill fragmentation of some tests, indicates their re-elaboration from older deposits. Because all of these foraminifers share the same taphonomic features and most of them represent taxa associated with deep-sea settings, they probably represent a flysch-type assemblage from an unknown deposit that was eroded and had its microfossils scattered through post-Paleogene sediments. A Paleocene age for this putative assemblage is indicated by the presence of Reticulophragmiun garcilassoi (Frizzell, 1943), a Paleocene index fossil, and by its association with the Cretaceous–Paleocene Ammodiscus pennyi Cushman and Jarvis, 1928. If taken as a coherent foraminiferal assemblage, it represents one of the few deep-sea assemblages known for West Antarctica, and the first flysch-type assemblage recognized for the Antarctic Cenozoic. In addition, it would show that the Paleocene foraminiferal communities of the West Antarctica's deep-sea floor were more like their Pacific counterparts than their Atlantic equivalents.UUID: http://zoobank.org/0d281489-c0c6-47b4-9884-f820806485b7

Life history of the deep-water persimmon eelpout (Eucryphycus californicus, family: Zoarcidae), and its use of drift vegetation as an ecological subsidy

The Persimmon Eelpout (Eucryphycus californicus) is a relatively unknown, deep-sea fish inhabiting temperate marine waters on the west coast of North America. Using samples collected in the mid-1970s, the most recent targeted sampling for this species, we present basic life history attributes, and an analysis of the relationship between E. californicus and drift macrophyte habitat in the Monterey Canyon, California, USA. A diet analysis revealed that the fish consumes predominantly small crustaceans, especially amphipods and copepods, including species that associate with drift macrophyte habitat. Otoliths were analyzed to yield age estimates ranging from 0 to 6 years, and growth was modeled showing a maximum length of 203 mm for males and 271 mm for females. An analysis of the reproductive ecology of E. californicus showed that like many deep-sea fishes, females lay relatively few, large eggs. The species exhibits a protracted spawning period, and females spawn with only one functional ovary. Empirical information presented in this paper and anecdotal evidence shows that E. californicus likely relies on drift algae and seagrasses, a habitat subsidy exported to the deep-sea environment from adjacent kelp forest ecosystems, for shelter and to concentrate food resources. This example of a species dependent on an ecosystem subsidy adds to our knowledge regarding the effects of cross-ecosystem connectivity in the marine environment, and furthers our understanding of the ecology of the deep-sea macrofaunal assemblage in Monterey Bay.

A unique and threatened deep water coral-bivalve biotope new to the Mediterranean Sea offshore the Naples megalopolis

The Gulf of Naples is an example of the most beautiful and biodiverse marine regions of the Mediterranean Sea and of the most impacted areas in terms of industrial activities, large contaminated areas, resource exploitation, infrastructures at sea and maritime transportation. We conducted Remotely Operated Vehicle surveys in the Dohrn Canyon in the Tyrrhenian Sea at approximately 12 NM off Naples metropolitan area, and revealed a hotspot of deep-sea benthic biodiversity of sessile fauna at ca. 400 m depth. The hard bottoms are characterized by a high abundance of charismatic species, such as the habitat forming cold-water corals (CWC) Madrepora oculata, Lophelia pertusa, Desmophyllum dianthus in association with the large size bivalves Acesta excavata and Neopycnodonte zibrowii. This CWC-bivalve co-occurrence represents a novel biotope for the Mediterranean Sea, which coexists with the evidence of severe anthropogenic threats, such as illegal dumping and fishery malpractices that were visually documented during the survey. We recommend the adoption of specific protection measures to preserve these unique deep-sea assemblages showing the uncommon co-existence of such a number of deep-sea species in a single habitat.

Distribution and diversity of polychaetes along a bathyal escarpment in the western Mediterranean Sea

Knowledge of the diversity of deep-sea polychaetes in the Mediterranean Sea is still scarce and fragmentary, due to the absence of comprehensive taxonomic revisions of several families, with the majority of recent works relying on higher level taxonomy. In the present work samples were collected with a box-corer along the Sardinian Slope, a bathyal escarpment area located in the western Mediterranean Sea, at seven depth levels separated from each other by a 300 m interval, ranging from 600 to 2400 m. Samples were sifted with a 0.3 mm mesh, and polychaetes were identified at the lowest taxonomic level and characterised from the biogeographic and tropho-functional point of view. Ninety-seven taxa were recorded, 60 of which identified at the species level; eight taxa are likely to be undescribed species, possibly endemic to the Mediterranean Sea, whereas another seven are reported for the first time for the Mediterranean Sea. The majority of taxa shows an Atlantic-Mediterranean or strictly Mediterranean distribution, thus confirming the similarity between Atlantic and Mediterranean deep-sea assemblages, but also the unicity of the latter. Conversely, cosmopolitan taxa, usually considered common in deep-sea assemblages, represented a minor component. The trophic guild composition of the assemblage varied along the slope, with shallower assemblages (600–900 m) including a relatively high percentage of predators and microphagous omnivores, while deeper assemblages (1500–1800 m) showed a > 90% percentage of deposit- and filter-feeders, with the 1200 m assemblage characterised by intermediate features. This outcome suggests that in the presently investigated area, the environmental conditions of shallower samples allow the stable occurrence of at least two trophic levels, whereas deeper assemblages depend mainly on organic matter coming from shallower levels and from the water column. The examined polychaete assemblages are characterised by low density and a complete absence of dominance, with the evenness index J’ ranging from 0.72 to 1; the wide ranges of the H’ index (0.50–2.67) and of Hill's N1 (1.65–14.65) suggest a high variability at low spatial scale. If compared to Atlantic deep-sea polychaete assemblages the assemblage studied shows an almost ten-fold lower organism abundance, but species diversity is only two- to four-fold lower, suggesting that biodiversity in Mediterranean deep-sea environments is possibly underestimated. Diversity of polychaete assemblages in the deep Mediterranean Sea is likely to be underestimated due to their low density, and adequate sampling strategies should be planned to have a better insight into the functioning and diversity of these communities.

Spatial Variability of Picoeukaryotic Communities in the Mariana Trench

Picoeukaryotes play prominent roles in the biogeochemical cycles in marine ecosystems. However, their molecular diversity studies have been confined in marine surface waters or shallow coastal sediments. Here, we investigated the diversity and metabolic activity of picoeukaryotic communities at depths ranging from the surface to the abyssopelagic zone in the western Pacific Ocean above the north and south slopes of the Mariana Trench. This was achieved by amplifying and sequencing the V4 region of both 18S ribosomal DNA and cDNA using Illumina HiSeq sequencing. Our study revealed: (1) Four super-groups (i.e., Alveolata, Opisthokonta, Rhizaria and Stramenopiles) dominated the picoeukaryote assemblages through the water column, although they accounted for different proportions at DNA and cDNA levels. Our data expand the deep-sea assemblages from current bathypelagic to abyssopelagic zones. (2) Using the cDNA-DNA ratio as a proxy of relative metabolic activity, the highest activity for most subgroups was usually found in the mesopelagic zone; and (3) Population shift along the vertical scale was more prominent than that on the horizontal differences, which might be explained by the sharp physicochemical gradients along the water depths. Overall, our study provides a better understanding of the diversity and metabolic activity of picoeukaryotes in water columns of the deep ocean in response to varying environmental conditions.

Sensitivity of Bacterioplankton to Environmental Disturbance: A Review of Baltic Sea Field Studies and Experiments

Bacterioplankton communities regulate energy and matter fluxes fundamental to all aquatic life. The Baltic Sea offers an outstanding ecosystem for interpreting causes and consequences of bacterioplankton community composition shifts resulting from environmental disturbance. Yet, a systematic synthesis of the composition of Baltic Sea bacterioplankton and their responses to natural or human-induced environmental perturbations is lacking. We review current research on Baltic Sea bacterioplankton dynamics in situ (48 articles) and in laboratory experiments (38 articles) carried out at a variety of spatiotemporal scales. In situ studies indicate that the salinity gradient sets the boundaries for bacterioplankton composition, whereas regional environmental conditions at a within-basin scale, including the level of hypoxia and phytoplankton succession stages, may significantly tune the composition of bacterial communities. Also the experiments show that Baltic Sea bacteria are highly responsive to environmental conditions, with general influences of e.g. salinity, temperature and nutrients. Importantly, nine out of ten experiments that measured both bacterial community composition and some metabolic activities showed empirical support for the sensitivity scenario of bacteria – i.e. that environmental disturbance caused concomitant changes in both community composition and community functioning. The lack of studies empirically testing the resilience scenario, i.e. experimental studies that incorporate the long-term temporal dimension, precludes conclusions about the potential prevalence of resilience of Baltic Sea bacterioplankton. We also outline outstanding questions emphasizing promising applications in incorporating bacterioplankton community dynamics into biogeochemical and food-web models and the lack of knowledge for deep-sea assemblages, particularly bacterioplankton structure-function relationships. This review emphasizes that bacterioplankton communities rapidly respond to natural and predicted human-induced environmental disturbance by altering their composition and metabolic activity. Unless bacterioplankton are resilient, such changes could have severe consequences for the regulation of microbial ecosystem services.

Environmental controls on spatial variability of summer phytoplankton structure and biomass in the Bering Sea

The subarctic Bering Sea, one of the most productive regions of the world's oceans, is undergoing significant ecological shifts possibly linked to global climate change. During the Fourth Chinese National Arctic Research Expedition (CHINARE) from July 10 to 20 of 2010, phytoplankton community structure, species diversity, spatial distribution, community types, abundance and biomass variations were investigated in a large scale study extending from the Bering Strait into the open waters down to the subarctic Pacific. These patterns were linked to potential environmental drivers, including effects of water masses and seasonal sea ice retreat. Results showed a marked spatial zonation in the taxonomic composition, abundance and biomass. A total of 149 phytoplankton taxa distributed among 57 genera of 5 phyla were identified, characterized into three ecological groups, namely Arctic, Boreal-temperate and cosmopolitan species. Phytoplankton included 101 species of diatoms, 44 species of dinoflagellates, 2 species of Chrysophyta, 1 species of each Chlorophyta and Euglenophyta. Both abundance and biomass were highest in the Bering Shelf, moderate on the Bering Slope, and lowest on the Bering Basin. Chlorophyll a was found highest in the subsurface chlorophyll maxima (SCM) close to the thermocline and halocline layers but its depth varied regionally. Multi-dimensional scaling (MDS) revealed two types of assemblages, one a deep-sea assemblage associated with the Bering Basin and a neritic assemblage found in the Bering Slope and Shelf. Average abundance (10.22×103cells/L), biomass (0.43mg/m3), species diversity (2.60) and species richness (1.66) were established for deep-sea assemblage with the dominant species ranked as Neodenticula seminae, Chaetoceros atlanticus, Pseudonitzschia delicatissima, and Thalassionema nitzschioides. Neritic assemblage had higher values with 12.73×103cells/L, 2.41mg/m3, and 2.55 species richness but lower (2.41) species diversity, and the community was mainly dominated by Thalassiosira nordenskiöldii, Leptocylindrus danicus, Chaetoceros socialis, Chaetoceros debilis, Fragilariopsis oceanica, Nitzschia closterium and Chaetoceros furcellatus. A diatom bloom was observed near the Bering Strait in the summer of 2010 induced by high availability of nitrate particularly in the Bering Shelf, while water mass transportation mainly influenced communities in the Bering Basin and Slope. The observed fluctuation in both biomass and summer phytoplankton communities in the Bering Sea were mostly influenced by events related to the spring sea ice retreat in 2010.

Taxonomy and climatic zonation of the Late Quaternary bathyal ostracods from the Campos Basin, Brazil

This work represents a new contribution to the knowledge on deep-sea ostracods from the western South Atlantic Ocean based on the core GL77 drilled in the Campos Basin (40°02′50″W; 21°12′22″S), 1287m water depth. Radiocarbon dating and oxygen isotopic analyses in planktonic foraminifera indicate that the 275cm interval studied of this core comprises the marine isotope stages 1, 2 and 3 (approximately 45kyr). Forty ostracode species were identified, yet 19 of them are kept in open nomenclature due to either the absence of adult individuals or poor preservation. Thirteen of those species have been recorded previously in the Brazilian continental margin: Bythocypris kyamos, B. affinis, Cytheropteron inornatum, C. perlaria, K. coimbrai, K. morkhoveni, K. sinuosa, K. trinidadensis, Macrocypris adrecta, Microcythere dubia, M. cronini, Poseidonamicus pintoi and Saida ionia. A new Trachyleberididae species, Ambocythere circumporus nov. sp. is proposed, and Cobanocythere? dubia is reassigned to the genus Microcythere. The stratigraphic distribution of the species in the core GL77 was compared to other studies on deep-sea assemblages carried out in the western Atlantic Ocean. The general species diversity pattern is a significant reduction during the Last Glacial Maximum (LGM) followed by conspicuous changes in Holocene assemblages caused by the appearance of species absent in the Pleistocene. The species Bythocypris kyamos, Cytheropteron perlaria and Saida ionia are restricted to the Marine Isotope Stage (MIS) 1. Poseidonamicus pintoi and Australoecia sp. are predominant and almost exclusive to the MIS 2 and 3. These data indicate the possibility of elaboration of an ostracod-based paleoclimatic zonation for the Quaternary of the south/southeast Brazilian margin.

Deep-Sea, Deep-Sequencing: Metabarcoding Extracellular DNA from Sediments of Marine Canyons.

Marine sediments are home to one of the richest species pools on Earth, but logistics and a dearth of taxonomic work-force hinders the knowledge of their biodiversity. We characterized α- and β-diversity of deep-sea assemblages from submarine canyons in the western Mediterranean using an environmental DNA metabarcoding. We used a new primer set targeting a short eukaryotic 18S sequence (ca. 110 bp). We applied a protocol designed to obtain extractions enriched in extracellular DNA from replicated sediment corers. With this strategy we captured information from DNA (local or deposited from the water column) that persists adsorbed to inorganic particles and buffered short-term spatial and temporal heterogeneity. We analysed replicated samples from 20 localities including 2 deep-sea canyons, 1 shallower canal, and two open slopes (depth range 100–2,250 m). We identified 1,629 MOTUs, among which the dominant groups were Metazoa (with representatives of 19 phyla), Alveolata, Stramenopiles, and Rhizaria. There was a marked small-scale heterogeneity as shown by differences in replicates within corers and within localities. The spatial variability between canyons was significant, as was the depth component in one of the canyons where it was tested. Likewise, the composition of the first layer (1 cm) of sediment was significantly different from deeper layers. We found that qualitative (presence-absence) and quantitative (relative number of reads) data showed consistent trends of differentiation between samples and geographic areas. The subset of exclusively benthic MOTUs showed similar patterns of β-diversity and community structure as the whole dataset. Separate analyses of the main metazoan phyla (in number of MOTUs) showed some differences in distribution attributable to different lifestyles. Our results highlight the differentiation that can be found even between geographically close assemblages, and sets the ground for future monitoring and conservation efforts on these bottoms of ecological and economic importance.

Molluscan assemblages under the influence of peat-draining rivers off East Sumatra, Indonesia

The central Indo-west Pacific biodiversity hotspot is of outstanding biological interest in terms of both taxonomy and ecology. However, the molluscan fauna of the region is poorly known. Here we present death assemblages of the subtidal (1–56 m) waters off Eastern Sumatra, Indonesia. Molluscan shells were sampled from a variety of settings from estuaries to coral reef-related carbonate environments. A total of 5064 shells was counted and 197 species were identified. Four shelly death assemblages which are defined by characteristic taxa are found in specific environments. A deposit-feeding community with low diversity and low abundances was recorded in settings with high amounts of terrigenous mud. Greater abundances and higher diversity were found farther offshore, especially in carbonate sediments in the vicinity of offshore islands where pteriomorphian bivalves are characteristic taxa. Protobranch bivalves, especially a species of Nuculana, appear to be best adapted to the organic-rich but food-limited, muddy substrate of the proximal marine environment influenced by peat-draining rivers. Thus, in addition to dominating deep-sea molluscan assemblages, some protobranch bivalves appear to be specialists in exploiting refractory organic materials of shelf environments.

Temperature impacts on deep-sea biodiversity.

Temperature is considered to be a fundamental factor controlling biodiversity in marine ecosystems, but precisely what role temperature plays in modulating diversity is still not clear. The deep ocean, lacking light and in situ photosynthetic primary production, is an ideal model system to test the effects of temperature changes on biodiversity. Here we synthesize current knowledge on temperature-diversity relationships in the deep sea. Our results from both present and past deep-sea assemblages suggest that, when a wide range of deep-sea bottom-water temperatures is considered, a unimodal relationship exists between temperature and diversity (that may be right skewed). It is possible that temperature is important only when at relatively high and low levels but does not play a major role in the intermediate temperature range. Possible mechanisms explaining the temperature-biodiversity relationship include the physiological-tolerance hypothesis, the metabolic hypothesis, island biogeography theory, or some combination of these. The possible unimodal relationship discussed here may allow us to identify tipping points at which on-going global change and deep-water warming may increase or decrease deep-sea biodiversity. Predicted changes in deep-sea temperatures due to human-induced climate change may have more adverse consequences than expected considering the sensitivity of deep-sea ecosystems to temperature changes.

First glimpse into Lower Jurassic deep-sea biodiversity: in situ diversification and resilience against extinction.

Owing to the assumed lack of deep-sea macrofossils older than the Late Cretaceous, very little is known about the geological history of deep-sea communities, and most inference-based hypotheses argue for repeated recolonizations of the deep sea from shelf habitats following major palaeoceanographic perturbations. We present a fossil deep-sea assemblage of echinoderms, gastropods, brachiopods and ostracods, from the Early Jurassic of the Glasenbach Gorge, Austria, which includes the oldest known representatives of a number of extant deep-sea groups, and thus implies that in situ diversification, in contrast to immigration from shelf habitats, played a much greater role in shaping modern deep-sea biodiversity than previously thought. A comparison with coeval shelf assemblages reveals that, at least in some of the analysed groups, significantly more extant families/superfamilies have endured in the deep sea since the Early Jurassic than in the shelf seas, which suggests that deep-sea biota are more resilient against extinction than shallow-water ones. In addition, a number of extant deep-sea families/superfamilies found in the Glasenbach assemblage lack post-Jurassic shelf occurrences, implying that if there was a complete extinction of the deep-sea fauna followed by replacement from the shelf, it must have happened before the Late Jurassic.

Deep-sea nematode assemblages from a commercially important polymetallic nodule area in the Central Indian Ocean Basin

The Central Indian Ocean Basin (CIOB) is an important area for prospective mining for polymetallic nodules. However, little is known about the biodiversity or community structure of abyssal benthic assemblages in the area. The aim of this study was to investigate nematode assemblages inhabiting nodule fields in the CIOB in terms of species composition, diversity, density, biomass, size spectra and sex ratio. Samples were collected by box corer from a depth of 5000–5100 m during the 39th cruise of RV Akademik Boris Petrov in 2009. In total, 1066 individuals were examined from 4 stations and 16 samples. The total average density of nematodes recorded in the CIOB was considerably lower than reported from other deep-sea regions (27.17 ± 2.7 inds/10 cm2). Nematode diversity was comparable with that of other deep-sea regions and the composition of the dominant taxa was typical for oceanic basins. A total of 284 morphotypes belonging to 113 genera and 30 families were identified. Chromadoridae (29.6%), Xyalidae (19.3%), Oxystominidae (6.6%) and Desmoscolecidae (5.0%) were the dominant families. Among the genera, Acantholaimus (23.2%), Halalaimus (5.7%), Desmoscolex (4.8%), Theristus (3.5%) and Daptonema (3.4%) were the most numerous. The majority of specimens had a body length in the range of 1000–1500 µm, which is also in accordance with other deep-sea studies. Females were three times more abundant than males at all CIOB stations. Average total nematode biomass (52.39 ± 10.0 mg/m2) was comparable with macrofauna biomass from the same area.

Living benthic foraminifera: biogeographical distributions and the significance of rare morphospecies

Abstract. Previous studies have investigated regional distribution but this is the first attempt to investigate the global biogeographical distribution of individual morphospecies of living/stained smaller benthic foraminifera. From 8032 samples collected between 1952 and 2011 data have been gathered on the relative abundance of >120 species in five major environments ranging from marsh to deep sea. There is a spectrum of six groups of species with abundance ranging from very high (Group 1) to extremely low (Group 6). In the latter species abundance never reaches 10% of an assemblage and, in many cases, it is only 1–2%. Individual species are shown to occupy a range of environments with very few being confined to a single environment (usually either marsh or deep sea). Some species occur in several oceans while others are confined to just one. There is no correlation between species abundance and being either widely or narrowly distributed. Propagules are the most likely mechanism of dispersal but some narrowly distributed species may not produce them. Generalists may be widely or narrowly distributed but opportunists are likely to be widely distributed. The rare species of Group 6 contribute to high diversity in shelf and deep-sea assemblages. These species may be adapted to minor differences in microhabitats induced by disturbance and patchy food supply. Patterns of biogeography have application to ecology, palaeoecology and taxonomy.

Elucidating trophic pathways in benthic deep-sea assemblages of the Mid-Atlantic Ridge north and south of the Charlie-Gibbs Fracture Zone

The Mid-Atlantic Ridge (MAR) is a topographically complex feature in the North Atlantic Ocean with little exploration of benthic fauna except in association with hydrothermal venting, resulting in the biodiversity and ecosystem functioning of the MAR benthos away from these sites remaining largely unknown. Stable isotope analysis of carbon, nitrogen and sulphur were undertaken on fauna collected north and south of the Charlie-Gibbs Fracture Zone, in areas believed to be devoid of hydrothermal venting, to investigate the trophodynamics of the benthic assemblage. δ13C and δ34S values of the benthic and bentho-pelagic fauna indicated a dependence on photosynthetic primary production, with no influence from an unknown chemosynthetic source. A large trophic discrimination in δ13C between consumers and potential food sources (particulate organic matter and surficial sediments) suggested reworking of organic carbon before assimilation by benthic fauna. Interpretation of sediment δ15N values was difficult as these ranged between −0.74 and 23.14‰, suggesting further work is required to understand nitrogen utilisation by benthic deposit feeders. Differences in trophic guilds (predators, predator–scavenger, surface deposit feeders, subsurface deposit feeders and suspension feeders) were evident for δ13C and δ15N, with the main difference between the mobile predators–scavengers and the benthic deposit feeders. Dividing the assemblage based on trophic guilds into food chains dependent on phytodetritus (deposit and suspension feeders) and predation–scavenging (fishes and crustaceans) resulted in strong positive correlations between δ15N and δ13C at both stations. These reflected the 2 dominant trophic pathways organic matter passed through deposit feeders and predatory and scavenging deep-sea fishes and crustaceans.

Deep-sea fish assemblages in the Colombian Caribbean Sea

Studies of the species composition, relative abundance and biomass of deep-sea assemblages are needed to create a knowledge base for the assessment of the resource potential and to advise ecosystem-based conservation and fisheries management strategies. This study attempts to create an initial knowledge base of the system by assessing the deep-sea fish assemblages of Colombian Caribbean Sea across a depth range of 200–550m. A total of 102 species (13 Chondrichthyes and 89 Teleosteans) and 58 families (9 Chondrichthyes and 49 Teleosteans) of deep-sea fish were sampled. This study reveals the existence of three deep-sea fish assemblages and demonstrates that depth plays an important role in ichthyofaunal group differentiation. Most species of the shallower assemblage exhibited a narrow depth range, while species of middle depth assemblage showed the widest depth range. From the point of view of conservation and fisheries management strategies, we need to know the status of deep-sea fish assemblages more fully before initiating a new deep-sea fishery in the Colombian Caribbean Sea. Conservation and protection of the habitats is therefore fundamental to develop a rational and sustainable management of the deep-sea fishery resources of the Colombian Caribbean Sea.

Pockmarks enhance deep‐sea benthic biodiversity: a case study in the western Mediterranean Sea

AbstractAim Pockmarks are craters on the sea floor formed by sub‐sea‐floor fluid expulsions, which occur world‐wide at all ocean depths. These habitats potentially host a highly specialized fauna that can exploit the hydrocarbons released. Pockmarks at relatively shallow depths can be easily destroyed by human activities, such as bottom trawling. In the present study, we investigated the combined effects of sea‐floor heterogeneity, rate of fluid emission and trophic conditions of different pockmarks on the biodiversity of the deep‐sea assemblages.Location Continental slope of the Gulf of Lions, western Mediterranean Sea, at water depths from 265 to 434 m.Methods We investigated the biodiversity associated with sea‐floor pockmarks that are both inactive and that have active gas emissions. Control sites were selected on the sea floor outside the influence of the gas seepage, both within and outside the pockmark fields. We examined the combined effects of: (i) sea‐floor heterogeneity; (ii) variable levels of fluid (gas) emissions; and (iii) trophic characteristics of the meiofaunal assemblage structure and nematode diversity.Results Sediments within the pockmark fields had lower meiofaunal abundance and biomass when compared with the surrounding sediments that were not influenced by the gas seepage. Although several higher taxa were absent in the pockmarks (e.g. Turbellaria, Tardigrada, Cumacea, Isopoda, Tanaidacea, Nemertina and Priapulida, which were present in the control areas), the richness of the nematode species within all of these pockmarks was very high. About 25% of the total species encountered in the deep‐sea sediments of the investigated areas was exclusively associated with these pockmarks.Main conclusions We conclude that both active and inactive pockmarks provide significant contributions to the regional (gamma) diversity of the continental slope in the western Mediterranean Sea, and thus the protection of these special and fragile habitats is highly relevant to the conservation of deep‐sea biodiversity.