Trophic relationships in deep-water decapods of Le Danois bank (Cantabrian Sea,NE Atlantic): Trends related with depth and seasonal changes in food quality and availability

The trophic relationships of decapod crustaceans on Le Danois bank (NE of Iberian Peninsula, NE Atlantic Ocean) were studied within the framework of the multidisciplinary project ECOMARG during two surveys, one in October 2003 and the other in April 2004. The diets of eleven species of decapods were analyzed and, within a rather continuous gradient of food source exploitation, 3 trophic groups were identified: (1) plankton feeders, comprising the shrimps Acanthephyra pelagica, Sergia robusta, and Pasiphaea tarda, which preyed on meso-bathypelagic taxa such as euphausiids and calanoids; (2) benthos feeders, comprising the crangonids Pontophilus norvegicus and Pontophilus spinosus, the crab Geryon trispinosus and the shrimp Aristeus antennatus; and (3) an intermediate group, including the rest of species, with mixed diets that included detritus. Among the third group, anomurans (Munida tenuimana, Pagurus alatus, and Parapagurus pilosimanus) consumed phytoplanktonic detritus in April, suggesting a link with peaks of surface Chl a occurring between March and April in the study area. Gut pigment and isotopic (δ¹³C/δ¹⁵N correlations) analyses revealed that assemblages inhabiting the top of the bank (455–612 m) and the inner basin (642–1048 m, close to the Lastres canyon head) had different food sources, with species inhabiting the deepest region exhibiting a stronger dependence on marine snow derivatives. These results are consistent with the higher proportion of mud and sediment organic matter (OM) content in the inner basin (82.2% pellites; 6.3% OM at 1028 m) compared to the top of the Le Danois bank (only 13.9% pellites; 2.8% OM at 485 m), which is a hydrodynamically more active zone. Exploitation of different food sources is also consistent with differences in the trophic level of species, inferred from stable δ¹⁵N isotope analyses, which yield values ranging from 6.88‰ for the hermit crab P. alatus to 13.52‰ for the crangonid shrimp P. norvegicus. Stomach fullness was higher in April 2004 than in October 2003, both between and within species of the dominant decapods, including detritus feeders (M. tenuimana) and benthos feeders (e.g. G. trispinosus, P. norvegicus). Most species exhibited a parallel increase in their density in April 2004, with a significant positive correlation between density and stomach fullness. This increase coincides with a peak of surface Chl a concentration occurring in March–April.     

Volcanic rocks from Rosemary Bank (Rockall Trough,NE Atlantic)

A collection of basalts dredged from the southern flank of Rosemary Bank in the Rockall Trough is described. All samples are highly altered, the introduction of large amounts of CaCO₃ into the rocks being particularly notable. Normative calculations suggest that the basalts are transitional or mildly alkaline in character. Several trace elements appear to have been immobile during the process of secondary alteration and are used to infer the tectonic setting of Rosemary Bank at the time of its formation. Employing the discrimination techniques of Pearce and Cann, the basalts are shown to have oceanic affinities. However, caution has to be exercised in interpreting the trace element results in terms of sea-floor spreading in the Rockall Trough since some Scottish basalts extruded on to continental crust have similar compositions. A minimum age of Eocene has been obtained for Rosemary Bank.     

Crustacean decapod assemblages associated with fragmented Posidonia oceanica meadows in the Alboran Sea (Western Mediterranean Sea): composition,temporal dynamics and influence of meadow structure

The decapod assemblage associated with a Posidonia oceanica meadow located near its western limit of biogeographic distribution was studied over an annual cycle. Fauna samples were taken seasonally over a year (five replicates per season) in two sites located 7 km apart, using a non‐destructive sampling method (airlift sampler) for the seagrass. The dominant species of the assemblage, Pisidia longimana, Pilumnus hirtellus and Athanas nitescens, were associated with the protective rhizome stratum, which is mainly used as a nursery. The correlations between decapod assemblage structure and some phenological parameters of the seagrass shoots and wave height were negative or null, which reflects that species associated with the rhizome had a higher importance than those associated with the leaf stratum. The abundance and composition of the decapod assemblage as well as the ecological indexes displayed a seasonality trend with maximum values in summer‐autumn and minimum in winter‐spring, which were related to the seawater temperature and the recruitment periods of the dominant species. The spatial differences found in the structure and dynamics of the assemblages may be due to variations in the recruitment of the dominant species, probably as a result of the influence of local factors (e.g. temperature, currents) and the high dispersal ability of decapods, together with the patchy configuration and the surrounding habitats. The studied meadows are fragmented and are integrated within a mosaic of habitats (Cymodocea nodosa patches, algal meadows, rocky and sandy bottoms), which promotes the movement of individuals and species among them, maintaining a high species richness and evenness.     

Contrasting life-histories,secondary production,and trophic structure of Peracarid assemblages of the bathyal suprabenthos from the Bay of Biscay (NE Atlantic) and the Catalan Sea (NW Mediterranean)

The life-histories and the secondary production of four dominant peracarid crustaceans (the mysids Boreomysis arctica and Parapseudomma calloplura, the amphipod Rhachotropis caeca, and the isopod Ilyarachna longicornis) in bathyal depths of the Bay of Biscay (NE Atlantic; between 383 and 420 m) and the Catalan Sea (Northwestern Mediterranean; between 389 and 1355 m) were established. Both the Atlantic and the Mediterranean populations of the major part of the target-species had two generations/year with mean cohort-production intervals (CPI) ranging from 5.5 mo for Ilyarachna longicornis to 6.3 mo for Parapseudomma calloplura. The Hynes method showed secondary production to vary in the Bay of Biscay between 0.113 mg DW m⁻² yr⁻¹ for I. longirostris and 3.069 mg DW m⁻² yr⁻¹ for P. calloplura, with P/B ratios between 4.57 (I. longirostris) and 7.93 (Boreomysis arctica). In the Catalan Sea, production varied between 0.286 mg DW m⁻² yr⁻¹ for I. longirostris and 1.096 mg DW m⁻² yr⁻¹ for P. calloplura, with P/B between 5.72 (I. longirostris) and 6.66 (P. calloplura). Application of two different empiric models to the whole peracarid assemblage gave similar levels of secondary production in both study areas (between 29.26 and 32.14 mgDWm⁻² yr⁻¹ in the Bay of Biscay; between 26.23 and 26.54 mg DW m⁻² yr⁻¹ in the Catalan Sea). From the analysis of gut contents of 22 species the dominant species in each study area were assigned to two basic trophic levels, detritus feeders and predators. Also, cumulative curves of dominance showed high diversity (low dominance) for peracarid assemblages distributed at mid-bathyal depths (524–693 m) both in the Bay of Biscay off Arcachon and in the Catalan Sea off Barcelona. We also discuss and compare, both within and between areas, how environmental features may explain the observed diversity patterns, the trophic structure, and the production results obtained for the suprabenthos assemblages.     

Temporal changes in the structure of the crustacean decapod assemblages associated with Cymodocea nodosa meadows from the Alboran Sea (Western Mediterranean Sea)

The decapod assemblages associated with two shallow meadows of Cymodocea nodosa, located in the same geographical area (Southern Spain) but on different substrates and with different patch size, have been analyzed. They display similar structure (diversity indices not significantly different), without a clear relation of richness and abundances to patch size, and with the same dominant species (the family Hippolytidae and, in particular, Hippolyte leptocerus are characteristic of this habitat). The composition of both crustacean assemblages is influenced by species that are common in neighbouring habitats. Therefore the connectivity among them is an important factor in the qualitative and quantitative structure of these decapod communities. Species richness appears to be higher than in Cymodocea meadows elsewhere in the Mediterranean and Atlantic at a similar depth, perhaps as a consequence of the biogeographical location and the high diversity and connectivity with surrounding biotopes. High evenness values are the result of the structure and location of these meadows, which are fragmented and interspersed with other biotopes (sandy and rocky bottoms), resulting in an ‘ecotone effect’. On the other hand, the structures of the decapod assemblages differ significantly according to sampling period. The abundance and species richness are both related to plant phenology and the dominant species present a positive correlation with the number of leaves per shoot. The maximum abundance of many species is coincident with the greatest seagrass development (spring – summer), which provides more resources (surface, biomass, protection, food). Therefore, seasonality is linked to plant life cycle, but also to the interrelationships and biology of the species, which are adapted and specialized to the environmental features of these shallow habitats.     

Seismic and oceanographic evidence of present-day bottom-water dynamics in the Lousy Bank—Hatton Bank area,NE Atlantic

High-resolution multi-channel seismic records from the eastern margin of the Iceland Basin, Northeast Atlantic, are used to infer regional patterns of bottom water dynamics from seafloor morphology and distribution of the most recent geological units deposited along the margin. This information is combined with results from oceanographic and hydrodynamic measurements made in the area. The study area is located between Lousy Bank and Hatton Bank, where deep-water currents are forced around structural highs, leaving a complex pattern of topographically controlled sediment transport pathways. At the top and upper flank of Lousy Bank, George Bligh Bank and Hatton Bank topographic forcing leads to considerable acceleration of the northward flowing North Atlantic Current. At greater water depth, seismic facies indicative of bottom current action are found to be widespread. In addition, seafloor morphology displays moat features extending over large distances. The occurrence of these moats is confined to specific water depths in the range from 700–1400 m and from 1800 to 2200 m depth range. These depth ranges correspond to the basal depth stratum of the North Atlantic Current and the depth range of the Deep Northern Boundary Current, respectively. Geological evidence suggests maximum near-bottom current speed of about 0.5 m/s for these moat areas. Using oceanographic data we suggest that formation of the moats is not likely to be associated with the presence of a persistent high-speed contour current core, but probably originates from the occurrence of solibores and thus may be related to the internal wave field of the Iceland Basin possible linked to atmospheric pressure variation.     

Deep-sea macrofaunal assemblages within the Benthic Boundary Layer of the Cap-Ferret Canyon (Bay of Biscay,NE Atlantic)

The Benthic Boundary Layer (BBL) assemblages from the Cap-Ferret Canyon (Bay of Biscay) were quantitatively sampled at two sites located within its main channel near mooring deployments (Mooring Sites MS 1: ca. 2400 m; MS 2: ca. 3000 m) with a suprabenthic sled equipped with four nets fishing at different heights above the bottom. The macrofaunal abundance above the sea-floor was mainly represented by Isopoda (42.2%), Amphipoda (19.0%), Euphausiacea (17.3%), Cumacea (13.5%), Mysidacea (2.8%) and Tanaidacea (2.6%). At both sampling sites, the highest total densities were generally recorded in the immediate vicinity of the sea floor (10–40 cm water layer), and a drastic decrease occurred higher in the BBL community. The BBL assemblages from the two sampling sites were similar in their faunal composition (major taxa), and their mean density estimates were not statistically different (MS 1 : 525.3 ind. 100 m⁻²; MS 2 : 283.3 ind. m⁻²) although the recorded values during each cruise were always lower at the deeper site. The BBL macrofauna abundance showed obvious temporal fluctuations at both sites, probably linked with a seasonal organic input from the euphotic zone (vertical flux) via phytodetritus deposition on the sea bottom.     

Evidence for current-controlled morphology along the western slope of Hatton Bank (Rockall Plateau, NE Atlantic Ocean)

A multibeam bathymetric and high- (airgun and sparker) to very high-resolution (Topas) seismic study of the western slope of Hatton Bank (NE Atlantic), located between 600 m and 2,000 m water depth, has revealed a highly variable range of current-controlled morphological features. Two major seabed areas can be distinguished: (1) a non-depositional area corresponding to the top of the bank and (2) a depositional area in which the Hatton Drift has developed. Both areas are characterised by distinct morphologies associated either with rock outcrops and rocky ridges or with smooth surfaces, slides and bedforms controlled mainly by bottom currents interacting with the topography of the bank. The water depth separating the morphological areas probably coincides with the boundary of the Labrador Sea Water and the Lower Deep Water. Morphological features identified in the study area include contourite channels (moats, furrows and scours), fields of sediment waves, edges of contourite deposits, ponded deposits, scarps, gullies, ridges, depressions, slides and slide scars. These morphological features do not necessarily reflect present-day conditions but may have been associated with past current events, consistent with earlier interpretations.     

Influence of Late Quaternary depositional environments on the structure of nannofossil assemblages in the Titanic area (northwestern Atlantic)

The nannofosssil assemblages have been analyzed in five cores taken from the Titanic area of the northwestern Atlantic (∼41°–42° N, ∼47°–50° W, water depths >3500 m) during cruises 41 and 43 of the R/V Akademik Mstislav Keldysh in 1998 and 2000. They correlate the host sediments with the upper Pleistocene-Holocene Emiliania huxleyi zone. The changes in the structure of the nannofossil assemblages and the lithological characteristics such as the content of biogenic CaCO₃, the abundance of ice-rafted debris, and the grain-size composition were used for the high-resolution stratigraphy of sections with defining marine isotopic stages 1–3 of the last 24 kyr. A characteristic feature of the nannofossil assemblages from this area is their enrichment with the cold-resistant species Coccolthus pelagicus during the warm climatic stages and the lack of allochthonous coccolitophorid remains.     

Imaging the recent sediment dynamics of the Galicia Bank region (Atlantic,NW Iberian Peninsula)

Multibeam bathymetry, high resolution multi-channel, and very high resolution single-channel (3.5 kHz) seismic records were used to depict the complex geomorphology that defines the Galicia Bank region (Atlantic, NW Iberian Peninsula). This region (≈620–5,000 m water depth) is characterized by a great variety of features: structural features (scarps, highs, valleys, fold bulges), fluid dynamics-related features (structural undulations and collapse craters), mass-movement features (gullies, channels, mass-flow deposits, slope-lobe complexes, and mass-transport deposits), bottom-current features (moats, furrows, abraded surface, sediment waves, and drifts), (hemi)pelagic features, mixed features (abraded surfaces associated to mixed sediments) and bioconstructions. These features represent architectural elements of four sedimentary systems: slope apron, contouritic, current-controlled (hemi)pelagic, and (hemi)pelagic. These systems are a reflection of different sedimentary processes: downslope (mass transport, mass flows, turbidity flows), alongslope (bottom currents of Mediterranean Outflow Water, Labrador Sea Water, North Atlantic Deep Water, and Lower Deep Water), vertical settling, and the interplay between them. The architectural and sediment dynamic complexities, for their part, are conditioned by the morphostructural complexity of the region, whose structures (exposed scarps and highs) favor multiple submarine sediment sources, affect the type and evolution of the mass-movement processes, and interact with different water masses. This region and similar sedimentary environments far from the continental sediment sources, as seamounts, are ideal zones for carrying out submarine source-to-sink studies, and can represent areas subject to hazards, both geologic and oceanographic in origin.     

Macrobenthic community structure over the continental margin of Crete (South Aegean Sea, NE Mediterranean)

Macrobenthic faunal composition, abundance, biomass and diversity together with a suite of sedimentary environmental parameters were investigated on a seasonal basis in order to determine factors regulating faunal distribution over the oligotrophic continental margin of the island of Crete (South Aegean Sea, North Eastern Mediterranean). Macrofaunal species composition was similar to that of the western Mediterranean and the neighboring Atlantic having several common dominant species. Mean benthic biomass, abundance and diversity decreased with depth, with a major transition zone occurring at 540 m, beyond which values declined sharply. At comparable depths biomass and abundance values were considerably lower to those found in the Atlantic, high-lighting the extreme oligotrophy of the area. The continental margin of Crete was characterised by a high diversity upper continental shelf environment (dominated by surface deposit feeding polychaetes) and a very low diversity slope and deep-basin environment (dominated by carnivorous and filter feeding polychaetes). Classification and ordination analyses revealed the existence of four principle clusters divided by a faunal boundary between 200 and 540 m, as well as beyond 940 m depth. Significant correlations between macrofauna and sediment parameters led to the conclusion that besides depth, food availability (as manifested by the concentration of chloroplastic pigments) is the principle regulating factor in the system. Such being the case, the prevailing hydrographic features that structure the pelagic food web and are directly responsible for the propagation of organic matter to the benthos also affect its community structure.     

Spatial patterns of zooplankton abundance,biovolume, and size structure in response to environmental variables: a case study in the Yellow Sea and East China Sea

The Yellow Sea(YS) and East China Sea(ECS) are highly dynamic marginal seas of the northwestern Pacific Ocean. To gain an in-depth understanding of zooplankton community structure,zooplankton abundance, biovolume, and size structure in summer 2017 in the YS and ECS were assessed using ZooScan imaging analysis. Zooplankton abundance and biovolume ranged 2.94–1 187.14 inds./m³ and 3.13–3 438.51 mm³/m³, respectively. Based on the biovolume data of the categorized si...     

Understanding spatial and temporal dynamics of key environmental characteristics in a mesotidal Atlantic estuary (Douro,NW Portugal)

Ecosystem management and decision making process are dependent of a good knowledge of ecosystem functioning. Conceptual models allow knowledge organization through representation of relationships between variables and processes, facilitating management decisions. In this study, spatial and temporal characterization of key environmental variables, as well as relationships between them, was studied aiming the design of a conceptual model of the Douro estuary. This temperate mesotidal estuary is limited upstream by a hydroelectric power dam that controls freshwater inflow and prevents the propagation of the tide upstream, which, in turn, influences water circulation and biogeochemical dynamics of the system. During one year, from December 2002 to December 2003, water column data were collected monthly at 10 stations along the estuary, during ebb and flood tides. Spatial and temporal variability of water column salinity, temperature, nutrients, phytoplankton biomass, total particulate matter (TPM), phytoplankton primary production (PP), faecal coliform bacteria (FC) and community respiration (CR) were analysed. Salinity stratification was assessed by means of the Estuary Number (Ne) and variation of this index as well as other key characteristics with river flow was analysed. Freshwater discharge controlled salinity stratification and freshwater residence time. Ne indicated that the Douro was stratified for river flows <300 m³ s⁻¹, and freshwater residence time was >1 day for the same conditions. A decaying exponential relationship between PP and river flow was found, whereas nitrate and TPM increased logarithmically and linearly, respectively, with river flow. Regarding spatial distribution, nitrate and PP decreased downstream, showing that the river was a source of nutrients and phytoplankton, while the opposite trend was found for TPM, FC, ammonium and CR. The latter increase was probably due to untreated sewage discharge in the urbanized middle and lower estuarine stretches. Reduction of nitrate coming from the watershed and of bacterial contamination in the urban stretches of this highly modified water body, according to the European Water Framework Directive, emerges as the main water quality issues for this estuarine ecosystem.     

Preliminary results on growth and movements of dogfish Scyliorhinus canicula (Linnaeus, 1758) in the Cantabrian Sea

In this paper we present the first results on growth of dogfish (Scyliorhinus canicula L.) obtained from size frequency distributions collected during bottom trawl surveys and from 19 recaptures to date from 2 153 tagged individuals. The surveys belong to a series carried out in autumn in the Cantabrian Sea by the Instituto Español de Oceanografía (1983–1995). The estimated parameters from the von Bertalanffy equation applying the Bhattacharya, Gulland and Holt and Ford-Walford methods were K of around 0.09-0.13, and a maximum length close to 89–98 cm. In addition, based on ten recoveries with reliable data of location we assume a priori that this species does not move long distances in the area of study.     

The benthopelagic fish fauna on the summit of Seine Seamount,NE Atlantic: Composition,population structure and diets

Benthopelagic fishes were sampled during three cruises to Seine Seamount, NE Atlantic, using bottom trawls and an epibenthic sledge. A total of 16 fish species were caught on the summit plateau of the seamount at 160–180 m depth, belonging to 15 different families. Four species were common to all types of trawls, whereas the other species were found only in part of the catches. Most fish caught were small species and typical for shelf and seamount communities. The most abundant fish was the snipefish, Macroramphosus spp., which was important also in terms of biomass. The population structure (size classes and length/weight relationships) of the five most abundant species (Macroramphosus spp., Capros aper, Anthias anthias, Callanthias ruber and Centracanthus cirrus) shows that usually two or three size classes, probably representing age groups (year classes), were present, and that growth rates were high. A stomach content analysis of these fishes revealed a predominance of pelagic prey, mainly small copepods. No indications for a seamount effect in terms of enhanced biomass or topographic blockage were found.     

Rates and regulation of nitrogen cycling in seasonally hypoxic sediments during winter (Boknis Eck,SW Baltic Sea): Sensitivity to environmental variables

This study investigates the biogeochemical processes that control the benthic fluxes of dissolved nitrogen (N) species in Boknis Eck – a 28 m deep site in the Eckernförde Bay (southwestern Baltic Sea). Bottom water oxygen concentrations (O_2−BW) fluctuate greatly over the year at Boknis Eck, being well-oxygenated in winter and experiencing severe bottom water hypoxia and even anoxia in late summer. The present communication addresses the winter situation (February 2010). Fluxes of ammonium (NH₄⁺), nitrate (NO₃⁻) and nitrite (NO₂⁻) were simulated using a benthic model that accounted for transport and biogeochemical reactions and constrained with ex situ flux measurements and sediment geochemical analysis. The sediments were a net sink for NO₃⁻ (−0.35 mmol m⁻² d⁻¹ of NO₃⁻), of which 75% was ascribed to dissimilatory reduction of nitrate to ammonium (DNRA) by sulfide oxidizing bacteria, and 25% to NO₃⁻ reduction to NO₂⁻ by denitrifying microorganisms. NH₄⁺ fluxes were high (1.74 mmol m⁻² d⁻¹ of NH₄⁺), mainly due to the degradation of organic nitrogen, and directed out of the sediment. NO₂⁻ fluxes were negligible. The sediments in Boknis Eck are, therefore, a net source of dissolved inorganic nitrogen (DIN = NO₃⁻ + NO₂⁻ + NH₄⁺) during winter. This is in large part due to bioirrigation, which accounts for 76% of the benthic efflux of NH₄⁺, thus reducing the capacity for nitrification of NH₄⁺. The combined rate of fixed N loss by denitrification and anammox was estimated at 0.08 mmol m⁻² d⁻¹ of N₂, which is at the lower end of previously reported values. A systematic sensitivity analysis revealed that denitrification and anammox respond strongly and positively to the concentration of NO₃⁻ in the bottom water (NO₃⁻_BW). Higher O_2−BW decreases DNRA and denitrification but stimulates both anammox and the contribution of anammox to total N₂ production (%R_amx). A complete mechanistic explanation of these findings is provided. Our analysis indicates that nitrification is the geochemical driving force behind the observed correlation between %R_amx and water depth in the seminal study of Dalsgaard et al. (2005). Despite remaining uncertainties, the results provide a general mechanistic framework for interpreting the existing knowledge of N-turnover processes and fluxes in continental margin sediments, as well as predicting the types of environment where these reactions are expected to occur prominently.     

Genetic structure and recent population expansion in the commercially harvested deep-sea decapod,Metanephrops challengeri (Crustacea: Decapoda)

ABSTRACT

Determining the genetic structure and population dynamics of harvested species are key aspects of effective fisheries management. New Zealand scampi (Metanephrops challengeri) is a species of nethropid lobster that supports a commercial fishery on the continental shelf and slope around New Zealand. To determine the genetic structure and historical population demography of New Zealand scampi, we sequenced a 623 base-pair fragment of the mitochondrial gene cytochrome c oxidase subunit one (CO1) from 321 individuals across six widely separated sites off the coast of mainland New Zealand and the subantarctic Auckland Islands, representing much of the species’ distribution. The Auckland Islands population was found to be genetically distinct from all other sampled populations, potentially resulting from an absence of continuous suitable habitat between the central-eastern South Island and the Auckland Islands. An isolation-by-distance pattern of genetic structure was also detected. With the exception of the Mercury Islands, all sampled populations showed signs of recent population expansion, potentially linked to changes in habitat availability during the glacial-interglacial cycles of the Pleistocene. We recommend that the current NZ scampi management areas and harvesting rates for each remain unchanged.     

Macrofaunal nematodes of the deep Whittard Canyon (NE Atlantic): assemblage characteristics and comparison with polychaetes

Large nematodes form an important component of deep‐sea macrofaunal assemblages, but are often considered to be part of the meiobenthos and are rarely studied. We analysed the standing stocks, diversity, and functional group and genus‐level composition of macrofaunal nematodes at lower bathyal depths (3,500 m water depth) in the Whittard Canyon system (NE Atlantic) and on the adjacent continental slope. Five replicate sample sets were obtained using a Megacorer, at four locations (three canyon branches, one slope). Sediment samples were processed on a 500‐μm mesh to provide both nematode and polychaete data from the same samples. The dominant nematode genera included Paramesacanthion, Metacylicolaimus, Cylicolaimus and Phanodermopsis. Nematode standing stocks (density and biomass) increased significantly from slope to canyon locations. Similarly, nematode dominance increased substantially (and diversity decreased) from slope to canyon locations. Nematode feeding groups and tail shape groups also appeared to exhibit common trends across study locations. Nematode genus‐level faunal composition varied significantly between slope and canyon locations. We describe and discuss the broadly similar trends detected in the matching polychaete data, noting some differences in the polychaete density and diversity responses. We suggest that the similar trends in macrofaunal nematode and polychaete ecology across our four study locations reflect responses to both changing sedimentology and food availability.