Deep-sea Benthic Fauna Research Articles

Pan-Atlantic Comparison of Deep-Sea Macro- and Megabenthos

Deep-sea benthic fauna is vital for a well-functioning marine ecosystem but is increasingly under threat from a changing environment. To monitor and conserve this fauna, an understanding of their large-scale spatial and bathymetric distribution and their environmental drivers is necessary. In this study, we conduct a multivariate analysis on abundance benthic fauna data collected at the phylum and multitaxon levels using an epibenthic sledge (EBS) across the Atlantic, and identify the environmental factors that affect such data. Our findings show a decrease in abundance with depth in most of the Atlantic but find relatively heterogeneous abundances with depth within the Southern Ocean. Principal component analyses indicate differences in environmental conditions south of the Antarctic Polar Front (~52° S), outlining contrasts in the quantities of macronutrients and physical factors. Despite this, community composition seemed markedly similar throughout the Atlantic with the Antarctic Circumpolar Current seemingly not affecting benthic community composition for higher taxonomic levels. Those differences that did occur were largely caused by benthic chlorophyll, benthic iron, and surface silicate through a Bio-ENV. Overall, we argue that further large-scale spatial and bathymetric distribution studies are important amid environmental changes that are driving shifts in benthic community abundance and composition.

Living benthic foraminiferal assemblages of a transect in the Rockall Trough (NE Atlantic)

Foraminifera are unicellular protists and play a major role in the deep-sea ecosystems. This study focusses on the faunal analysis of living benthic foraminiferal assemblages and their vertical distribution along a transect in the Rockall Trough in the NE Atlantic. Therefore, seven multicorer cores from the Rockall Trough (RT-1 – RT-7), NE Atlantic, were collected at water depths between 1008 and 2205 m on the RRS Discovery cruise DY051 in spring 2016.Surface sediment samples of the collected material were analysed up to 10 cm sediment depth for living (Rose Bengal stained) benthic foraminifera to gain insight into the recent distribution of the foraminiferal fauna. The cores were sliced from 0 to 3 cm into 0.5 cm intervals and from 3 to 10 cm in 1 cm slices. Sediments were divided into the fractions >125 μm and 125–63 μm by wet-sieving. The analysis showed that stations differed in live assemblages, diversity, abundances and vertical distribution. Standing stock values of 92–168 ind./10 cm2 for the total, 54–130 ind./10 cm2 for the calcareous and 24–59 ind./10 cm2 for the agglutinated assemblages were obtained.Living deep-sea foraminiferal assemblages differed between the three shallower (RT-1 – RT-3) and the four deeper sites (RT-4 – RT-7), indicating that the different water masses could be a main factor controlling the deep-sea benthic fauna in the Rockall Trough. This area is characterised by two main water masses: the upper more saline Eastern North Atlantic Water (ENAW) and the lower North Atlantic Deep Water (NADW).Basically, Nonionella iridea occurred at all sites, while Cibicidoides species (except C. wuellerstorfi) and Melonis barleeanus were limited to water depths between 1008 and 1610 m (RT-1 – RT-3). Soft-shelled foraminifera increased sharply with water depth. Saccamminid sp. 1 contributed significantly to this increasing proportion of soft-shelled individuals with its maximum at 1857 m water depth (RT-5). Further characteristics of this transect include a mass occurrence of Uvigerina mediterranea, which was only present at 1008 m (site RT-1) or Globobulimina sp. 1 with its highest densities at 1610 m (RT-4), where it accounted for 20% of the total living foraminiferal fauna. The general microhabitat preferences where consistent with those of other studies, although the Rockall Trough is a very dynamic region considering food supply or other physical parameters.

A baseline quantitative assessment of deep-sea benthic fauna of the Gulf of Aqaba (Northern Saudi Arabia, Red Sea)

The Gulf of Aqaba (hereafter ‘the Gulf’) is a narrow, semi-enclosed, warm, high saline, and oligotrophic water body. This baseline study provides the first quantitative data on deep-sea (207–1281 m depth) benthos of the Gulf. Fifty-five benthic species (predominantly polychaetes) with a density of 160–670 ind. m−2, species richness of 11–25, and Shannon-Wiener diversity (H′) of 3.14–4.17 bits. ind.−1 were recorded from nine stations. The density and H′ of benthos of the Gulf are comparable with those of the Red Sea, while both are lower than those reported from the Arabian Sea and the Mediterranean Sea. The good-high ecological status of benthic communities indicates the absence of major stress in the deep-sea habitats of the Gulf. As large-scale urbanization is proposed in the Saudi coastal areas of the Gulf, this study is expected to provide a baseline dataset for future environmental impact assessments.

Deep-sea temperate-tropical faunal transition across uniform environmental gradients

The biogeography of the deep-sea benthic fauna is uncertain due to the vast size and incomplete exploration of these environments. While shallow water assemblages are differentiated into tropical, temperate and polar faunas, it is unknown whether these units extend to lower depths. Here we use model-based and multivariate statistics to analyse megafaunal benthic samples along a 2300 km transect off the eastern Australian continental margin. We show that a temperate-tropical transition between 33-30°S occurs at both lower bathyal (~2500 m) and abyssal (~4000 m) depths. This transition occurs despite almost uniform temperature, salinity and dissolved oxygen concentrations occurring across latitudes at these depths. Conversely, the patterns are consistent with the flux of organic matter to the seafloor, which varies from being relatively high in the productive temperate off SE Australia to low levels in more-oligotrophic tropical waters. Biodiversity is not uniform across the deep-sea and regional-scale heterogeneity needs to be incorporated into marine park designs.

Naturally occurring hydrocarbon content and baseline condition of deep-sea benthic fauna from the Great Australian Bight

The deep sea (> 500 m) of the Great Australian Bight (GAB) has not been well studied even though it is believed to have high conservation values as evidenced by large marine reserves, and where adjacent (continental shelf) waters support important commercial fisheries and large populations of marine mammals. Recent interest in developing the region's deep-sea hydrocarbon resources has drawn attention to this sparsity of data and the need to characterise the region's benthic ecology in order to detect and understand any potential impacts linked to a developing oil and gas industry. To that end, we measured the naturally occurring hydrocarbon content and baseline condition of a variety of benthic fishes and invertebrates collected during two surveys of the continental slope and seabed geological features. A total of 225 individuals, representing 15 species (7 invertebrates and 8 fishes) were analysed for (i) polycyclic aromatic hydrocarbons (PAH) body burdens or biliary PAH metabolites; (ii) 7-Ethoxyresorufin O-deethylase (EROD), a commonly used oil exposure biomarker; and (iii) lipid profiles and histology. Hydrocarbon concentrations, although measurable at some sites, did not indicate any anthropogenic contamination or unequivocal hydrocarbon seepage. PAH body burdens in the invertebrate species were below the levels of detection, and phenanthrene metabolites showed differences between species of fish surveyed, but were consistently low relative to oil exposed fish. EROD levels varied between species but also did not indicate exposure to oil. Lipid levels were highly variable between individuals and sites, suggesting that a lipid-related metric would not be suitable for monitoring organism health. Histological analysis indicated no gross deformity or infection in either the liver, gill, kidney or spleen. Pathologies identified were of minimal pathological important and likely to be recoverable. Liver exhibited varying levels of lipid accumulation across all fish species. These results, obtained before the commencement of oil and gas industry activity, can be used as a part of a baseline benthic ecosystem characterisation to guide future ecological monitoring programs.

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-μm fraction of Megacorer samples (0–1cmlayer) collected at five different sites in the area of the Porcupine Abyssal Plain Sustained Observatory (NE Atlantic, 4850mwater depth). Three sites are located on the tops of small abyssal hills (200–500m 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.

Linkage of deep sea rapid acidification process and extinction of benthic foraminifera in the deep sea at the Paleocene/Eocene transition

AbstractOcean Drilling Program Leg 199 Site 1220 provides a continuous sedimentary section across the Paleocene/Eocene (P/E) transition in the carbonate‐bearing sediments on 56–57 Ma oceanic crust. The large negative δ13C shift in seawater is likely due to the disintegration of methane hydrate, which is expected to be rapidly changed to carbon dioxide in the atmosphere and well‐oxygenated seawater, leading to a reduction in deep‐sea pH. A pH decrease was very likely responsible for the emergence of agglutinated foraminiferal fauna as calcareous fauna was eliminated by acidification at the P/E transition at Site 1220. The absence of the more resistant calcareous benthic foraminifera and the presence of the planktonic foraminifera at Site 1220 is interesting and unique, which indicates that calcareous benthic foraminifera suffered greatly from living on the seafloor. Box model calculation demonstrates that, assuming the same mean alkalinity as today, pCO2 must increase from 280 ppm to about 410 ppm for the calcite undersaturation in the deep ocean and for the oversaturation in the surface ocean during the P/E transition. The calculated increased pCO2 coincides with paleo‐botanical evidence. The current global emission rate (∼7.3 peta (1015) gC/y) of anthropogenic carbon input is approximately 30 times of the estimate at the P/E transition. The results at the P/E transition give an implication that the deep sea benthic fauna will be threatened in future in combination with ocean acidification, increased sea surface temperature and more stratified surface water.

Distribution of cold-water corals in the Whittard Canyon, NE Atlantic Ocean

The deep-sea floor occupies about 60% of the surface of the planet and is covered mainly by fine sediments. Most studies of deep-sea benthic fauna therefore have concentrated on soft sediments with little sampling of hard substrata, such as rocky outcrops in submarine canyons. Here we assess the distribution and abundance of cold-water corals within the Whittard Canyon (NE Atlantic) using video footage from the ROV Isis. Abundances per 100m of video transect were calculated and mapped using ArcGIS. The data were separated into five substratum types, ‘Sediment’, ‘Mixed Sediment and Rock’, ‘Sediment Slope’, ‘Lophelia reef’ and ‘Lophelia and rock’. Abundance and community structure were compared. A maximum abundance of 855 coral colonies per 100m of ROV transect were observed with 31 coral types identified. Highest taxon richness was observed along a ‘Lophelia reef’ area, although a larger richness of Octocorallia was observed away from the ‘Lophelia reef’ areas. ‘Lophelia reef’ and ‘Lophelia and rock’ areas were found to have a different coral community structure from the other substratum types. We suggest this is the result of Lophelia outcompeting other coral types because there is increased coral taxon richness in areas without Lophelia. We also hypothesise that the hydrodynamic regime within the Whittard Canyon results in differences in organic matter input including higher quality food, in comparison with other deep-water environments, leading to changes in the coral communities.

Lower bathyal and abyssal distribution of coral in the axial volcanic ridge of the Mid-Atlantic Ridge at 45°N

The deep-sea floor below 3000m occupies 50% of the surface of the planet and is composed mainly of fine sediments. Most studies of deep-sea benthic fauna have concentrated on soft sediments with little sampling in rocky areas and even less on non-vent mid-ocean ridges. To assess the distribution and abundance of coral between 2500m and 3500m depths, video footage from the ROV Isis taken during a cruise to the Axial Volcanic Ridge (AVR) of the Mid-Atlantic Ridge at approx 45°30′ N was analysed. Abundances per 100m were calculated and mapped using Arc GIS, with a maximum of 59 being observed. 20 putative species were identified. Scleractinia were absent from the observed area and the coral fauna was dominated by Octocorallia. The data were separated into four substratum types, sediment, sloped rock, flat rock and mixed substratum, with both abundance and community being compared. Sedimented and rocky areas had different coral communities with sediment having a higher occurrence of Pennatulidae and Chrysogorgidae than rock. Sloped rock had the highest abundance of corals. We suggest that this increase in abundance reflects higher food availability as well as the solid substratum on which coral larvae settle.

Response of ostracods to abrupt climate changes in the Western Mediterranean (Gulf of Lions) during the last 30kyr

Abstract Global climate changes attract the attention of researchers working with paleoceanographic proxies for reconstructing past ocean circulation changes and the physico-chemical parameters that control environmental conditions. Moreover, recent studies highlight the importance of climate change on deep sea benthic biodiversity. Deep sea benthic fauna are not isolated from atmospheric processes and climate changes controlling surface ocean biota, for benthic assemblages respond to changing climatic conditions as well. Substrate and physico-chemical characteristics of bottom waters have particularly strong influence on ostracod species distribution in all marine settings, making them excellent environmental indicators. This paper focuses on changes in ostracod assemblages at MD99-2348 site, located on the continental slope of the Gulf of Lions to determine the relationship between climatic-driven oceanographic changes and ostracod diversity and abundance. High abundances of Henryhowella asperrima and Echinocythereis echinata during Heinrich events (HE1 and HE2) may result from increased oxygenation of the bottom water and a more pulsed supply of nutrients (organic matter). Formation of surface cold water that increases the oxygen content in deep layers in the water column is linked to the intensification of northerly wind (Tramontane and Mistral) in northwestern Mediterranean during the acme of HEs, when high latitudes bodies of cold air (Mobile Polar Highs) reach the Mediterranean area. Moreover, the concomitant high abundance of Krithe pernoides , which proved to be very sensitive to variable oxygen levels, probably records even shorter (millennial to centennial scale) climate oscillations. Changes in environmental conditions are illustrated by the shift of C . testudo–Loxoconcha spp. vs. Pseudocythere sp.– Macrocypris sp. that indicates detrital input, primary productivity and the possible impact of sea level oscillation on benthic assemblages since the LGM.

A natural history of the deep-sea aplacophoran Prochaetoderma yongei and its relationship to confamilials (Mollusca, Prochaetodermatidae)

Previously published studies are woven together into a natural history of a deep-sea aplacophoran mollusc species, Prochaetoderma yongei Scheltema, 1985, and its confamilial species in the Prochaetodermatidae. This amphi-Atlantic species occurs sometimes in great numbers at upper bathyal depths, rivaling polychaetes in numerical dominance. It appears to be an opportunist, with wide geographic and depth distribution, rapid development from lecithotrophic larva to settlement and maturity, and omnivory. A short illustrated morphological description using characters useful for identifying all prochaetodermatid species should prove useful to nontaxonomists whose business is the deep-sea benthic fauna.

Living deep-sea benthic foraminifera from the warm and oxygen-depleted environment of the Sulu Sea

The semi-enclosed, oligotrophic Sulu Sea is characterised by warm (ca. 10 °C) and oxygen-depleted ( 32 μm) from 56 samples (from surface down to 5 cm). The stained foraminiferal assemblages of the Sulu Sea comprised 285 species, including 137 agglutinated and 148 calcareous species. Standing stock values ranged from 595 individuals/10 cm2 on the continental slope to 100 individuals/10 cm2 in the abyssal zone. Generally, in the low-productivity and low-oxygen environment of the Sulu Sea, stained assemblages are characterized by low-standing stock values, moderate dominance and low diversity. The combination of poor rates of C org flux and low dissolved oxygen content in bottom waters are the main factors controlling the deep-sea benthic fauna in the Sulu Sea. The foraminiferal abundances in the upper bathyal zone respond to both food fluxes and oxygen concentrations. Most of the epifaunal, oxyphilic species have their lower limit of occurrence at a water depth of approximately 2000 m (dissolved oxygen <1.25 ml/l) in the Sulu Sea. At constantly dysoxic (<1 ml/l O2) sites from the lower bathyal and abyssal zone, the assemblages comprised low-oxygen tolerant species and are more dependant on C org fluxes. The correlations between benthic foraminiferal faunas and C org flux and dissolved oxygen values are very good, with correlation coefficients of r2=0.956r2=0.956 and 0.88, respectively. The living deep-sea foraminiferal assemblages consisted mainly of agglutinated tests, with dominant species such as Lagenammina difflugiformis, Ammoscalaria tenuimargo, various Reophax species, and small (<70 μm) trochamminaceans like Portatrochammina wiesneri. Stained individuals of the calcareous Parrelloides bradyi (type 2) occurred in low numbers at oxygen-poor sites, down to a depth of 5 cm in the sediment column. The only stained, calcareous, infaunal species found deeper than 4000 m was Valvulineria mexicana (average living depth of 3 cm). The general microhabitat preferences of common species were consistent with those from other studies, although due to the unique combination of poor food supply and dysoxic conditions, most of the infaunal species had shallower average living depths than those reported from other dysoxic locations.

A multiple-scale analysis of metazoan meiofaunal distribution in the deep Mediterranean Sea

In order to identify environmental factors driving the distribution and functioning of deep-sea fauna and the spatial scales of interactions, we carried out a multiple-scale investigation in the Mediterranean basin in which we compared two bathyal plains, located at the same depth (ca. 3000 m), but characterised by contrasting trophic conditions. We investigated meiofaunal abundance, biomass, community structure and biodiversity (expressed as richness of taxa) in relation to sediment characteristics, downward fluxes and food availability in the sediment. Samples were collected at all spatial scales (from small to macroscale) in two seasons. Our results indicated that deep-sea systems with different trophic conditions displayed different responses to the distribution of available energy and its spatio-temporal variability in the sediment. The analysis at a macroscale (>1000 km) indicated that meiofauna were controlled primarily by the trophic inputs to the deep-sea system. Spatial variability of meiofaunal parameters at a mesoscale (>50 km) was highest in the eastern Mediterranean and lowest in the western Mediterranean. Such differences are the consequence of the unpredictable inputs of organic matter in the oligotrophic eastern Mediterranean versus a more homogeneous distribution of food inputs in the mesotrophic western Mediterranean. At a smaller scale (local scale 7 km), in the western Mediterranean, the distribution of meiofaunal parameters was highly homogeneous, reflecting the homogeneous distribution of the food availability in the sediment. Our results indicated that the highly variable input and distribution of food sources in the deep eastern Mediterranean did not provide any “insurance” for the sustainability of the deep-sea faunal assemblages in the long term, thus leading to an uncoupling between resource availability and distribution of organisms. We conclude that the influence of energy availability on the deep-sea faunal distributions change at different spatial scales and that the analysis of spatial variability at mesoscales is crucial for understanding the relationships between deep-sea benthic fauna and environmental drivers.

PROCHAETODERMATIDAE OF THE EASTERN ATLANTIC OCEAN AND MEDITERRANEAN SEA (MOLLUSCA: APLACOPHORA)

The Prochaetodermatidae is a family of spiculose vermiform aplacophoran molluscs primarily of the deep-sea benthic fauna. They are ecologically important both in numbers and dominance as well as by their omnivory. In an ongoing effort, the authors are describing this significant deep-sea group from collections that have been made worldwide from conttinental shelves to hadal depths of >5,000 m. Here the eastern Atlantic and Mediterranean species are described, a matter of 14 species, half of them new. The genus Prochaetoderma is here redefined and restricted with a redescription of the type species and designation of a neotype. Whereas prochaetodermatid species were first all considered as belonging to Prochaetoderma, differences in spicule morphology fall into 5 discrete genera. Herein are given precise diagnoses and a a key to the following genera, accompanied by the species described here: Prochaetoderma Thiele, 1902: P. raduliferum (Kowalevsky, 1901), ? P. atlanticum new species, P. boucheti new species, P. yongei Schteltema, 1985; Chevroderma Scheltema, 1985: Ch. turnerae, Ch. gauson, Ch. scalpellum, all Scheltema, 1985: Claviderma new name: Cl. brevicaudatum new species, Cl. gladiatum (Salvini-Plawen, 1992), Cl. tricosum new species; Niteomica Ivanov, 1996b: N. hystrix new species; and Spathoderma Scheltema, 1985: S. clenchi Schelterma, 1985, S. alleni new species, S. grossum new species. In total, 3,568 specimens have been examined from depths between 50 and >5,000 m from the West European Basin, including the Bay of Biscay, the Mediterranean Sea, and the Iberian, Cape Verde, Guinea, Angola, and Cape Basins.

Concentrations of Hg, Cd, Cu, Zn, Fe and Mn in deep sea benthic fauna from the Southeastern Mediterranean Sea: A comparison study between fauna collected at a pristine area and at two waste disposal sites

Concentrations of Hg, Cd, Cu, Zn, Fe, and Mn were determined in five deep sea benthic fauna species: Polycheles typhlops, Acanthephyra eximia, Aristeus antennatus (Crustacea), Bathypterois mediterraneus, and Nezumia sclerorhynchus (Fish). Specimens were collected at two deep sea dump sites and at a deep sea control area in the southeastern Mediterranean sea, 1988–1995, within the framework of monitoring studies. Natural concentrations in the studied species were determined using specimens collected at a control site. The order of the natural metal concentrations found in the crustaceans was: Fe > Cu > Zn > Mn > Cd > Hg, while in the benthic fish the order was different: Fe > Zn > Mn > Cu > Hg ≥ Cd. Natural levels of Hg and Cd were high compared with the levels found in near shore species, probably as a result of specific feeding habits and physiological metal regulation of each species. Specimens collected at the dump sites were used as biomonitors to assess the impact of waste dumping operations. Comparison of results to the natural metal levels showed some significant differences among the sites, but no systematic trends. Rank score analysis based on metal contents of the fauna gave the lowest sum of scores to the control site, indicating probable effect of the disposal operations.

Bathymetric patterns of genetic variation in a deep-sea protobranch bivalve, Deminucula atacellana

The origin of the deep-sea benthic fauna is poorly understood and represents an enormous gap in our understanding of basic evolutionary phenomena. One obstacle to studying evolutionary patterns in the deep sea has been the technical difficulty of measuring genetic variation in species that are typically minute, rare, and must be recovered from extreme depths. We used molecular genetic techniques to quantify variation in the 16S rRNA mitochondrial gene within and among populations of the common protobranch bivalve Deminucula atacellana (Schenck, 1939). We analyzed 89 individuals from nine samples collected in the 1960s along a depth gradient from 1100 to 3800 m in the western North Atlantic. Genetic variability within populations is much lower than between populations, and peak haplotype numbers occur near the center of its depth distribution. Continental slope ( 2500 m) populations were genetically distinct despite the lack of any obvious topographic or oceanographic features that would impede gene flow. These findings indicate that the deep-sea macrofauna can have strong population structure over small (134 km) spatial scales, similar to that observed in shallow-water and terrestrial organisms. This surprisingly high biodiversity at the genetic level affords the potential for adaptation and evolutionary diversification, the ultimate historical causes of high species diversity in the deep-sea benthos.

Vertical zonation in the distribution of deep-sea benthic fauna in the ocean

Vertical zonation in the distribution of deep-sea benthic fauna in the ocean