Slope Off Research Articles

Ocellus-bearing Neobythites species (Teleostei: Ophidiidae) from the West Atlantic with description of a new species

Three species of the ophidiid genus Neobythites containing ocelli in the dorsal fin are known from the West Atlantic: Neobythites gilli Goode and Bean 1885, N. ocellatus Günther 1887 and N. monocellatus Nielsen 1999. In the year 2000, 18 specimens of Neobythites were caught on the upper continental slope off eastern Brazil. This is the first documented record of a Neobythites specimen off Brazil since the holotype of N. ocellatus was caught in 1873. Seventeen of the specimens are referable to N. ocellatus and one to N. monocellatus. Until now the distribution of N. ocellatus was considered to be from off Atlantic Florida, the Caribbean Sea and then a gap of 4500 km to the type locality off Brazil. However, the holotype and the 17 specimens differ from the more northerly recorded specimens in pattern and number of spots and ocelli on the dorsal fin. The 18 Brazilian specimens have two distinct ocelli, one near the origin of the dorsal fin and one above the midpoint of the fish, and further back occasionally a small, black spot, while the northern specimens occasionally have a small, black spot near the origin of the fin, a distinct ocellus above the midpoint and up to three ocelli further posteriorly. Consequently a new species, N. multiocellatus, is described based on 59 specimens from the Caribbean Sea to off Atlantic Florida. The record of the N. monocellatus specimen extends its distribution about 3000 km southwards. A comparison of the four ocellus-bearing species from the West Atlantic is made.

Summer diatom and dinoflagellate blooms in Lisbon Bay from 2002 to 2005: Pre-conditions inferred from wind and satellite data

Sea surface temperature (SST) and chlorophyll ( Chl) maps derived from satellite data, together with wind and phytoplankton cell concentration time-series, are used to characterize the wind forcing and the spatio-temporal SST/ Chl variability for periods preceding the summer (June–September) diatom and dinoflagellate blooms. The blooms (concentrations of cells higher than 200 × 10 3 cells l - 1 ) were identified in the weekly samples collected at the long-term phytoplankton study site in Lisbon Bay, from 2002 to 2005. It is shown that bloom detection at the site occurs either during upwelling events, i.e. when offshore northerly wind speed is greater than 5 m s - 1 for more than 5 days, or up to 4 days after wind relaxation. However, no direct relationship was found between the blooms and either the intensity or duration of the wind pulses. The satellite image sequences show that the Chl patterns in Lisbon Bay are strongly linked to the orientation and branching of the upwelling filament rooted at Cape Roca and the westward progression of the warm-core cyclones shed from the slope off Setúbal Bay. High Chl values are typically maintained throughout the upwelling cycle along the inshore boundary of the Roca filament, covering the whole bay during the intense wind phase. During the relaxation phase, there is a Chl increase concurrent with the contraction of the high Chl area to the northern part of the bay, associated with an inshore poleward current. It is proposed that the earlier setup of the offshore stratification conditions and the shedding of a slope eddy favored the bloom of dinoflagellates in July 2004, while the stable position of the main circulation features in July 2002 favored a diatom bloom. The results add further evidence that, in summer, the ocean circulation in the embayments south Cape Roca is dominated by the upwelling dynamics and plays a key role in the development of phytoplankton blooms off central Portugal.

Taxonomic revision of Ascidiacea (Tunicata) from the upper continental slope off north-western Australia

A collection of ascidians from 100–1000 m deep off the north-western coast of Australia has yielded 19 species, including one new, two possibly endemic to the north-western coast of Australia, four well-known Indo-west Pacific tropical species and 12 species known from the deeper waters of the western Pacific, of which 11 had not previously been recorded from off the western Australian coast or from other parts of the Indian Ocean. A third of these 12 species displays adaptations for a reduction in filter-feeding capacity, as do other known species from deeper slope and abyssal habitats. Nevertheless a connection with fauna of deep ocean basins of the Indian Ocean is not apparent at this stage. The full range of characters associated with species, genera and families are discussed, and those contributing to the identification of immature or mutilated specimens, as well as those relevant to an assessment of phylogenetic relationships, are emphasized.

Nuevo registro de Scalpellum projectum (Crustacea: Cirripedia: Thoracica: Scalpellidae) para el talud continental de Chile

The pedunculate barnacle Scalpellum projectum Nilsson-Cantell, 1930, was described based on benthic material from a telegraph cable recovered from deep waters off Antofagasta (~23oS). No new records have been reported for this species worldwide since its original description. Six adult females of S. projectum were collected during recent studies of communities associated with methane seeps. The material was taken from three stations located between 34o42' and 36o22'S and at depths of 846 to 922 m. We provide taxonomic information based on the external morphology of the specimens, whose sizes coincide in general terms with those of the original description. No male specimens were observed; these are smaller, aberrant in form, and live within the scuta in the capitulum of the females. With this second finding, the distributional range of this species, previously only reported for the slope off Chile, is extended about 17o latitude southwards (1,800 km) and its bathymetric range is expanded by 200 m.

NO TITLE AVAILABLE

A pesca demersal voltada as espécies de peixes (i.e. Lophius gastrophisus, Urophisys brasiliensis, Genipterus brasiliensis) e crustáceos (Chaceon ramosae e Chaceon sp.), com grande valor comercial no talude continental superior do sul do Brasil aumentou significativamente nas últimas décadas. A compilação de todos os dados até então publicados acerca dos pontos de ocorrência dos corais escleractíneos azooxantelados em águas sul-brasileiras entre 24° e 35° S, sobrepostos com as principais áreas de atuação das quatro modalidades de pesca demersais (arrasto de profundidade, emalhe e espinhel de fundo e covos), demonstrou que as frotas em questão vêm utilizando as áreas com ocorrência de corais, como principais áreas de esforço, indicando que os recifes de profundidade possuem elevada importância ecológica perante os ecossistemas da plataforma e talude continental, sendo importantes reservatórios da biodiversidade marinha profunda. Entretanto, desde as fases iniciais desta exploração evidenciou-se através de relatos de observadores de bordo, a captura, como "bycatch", de grandes quantidades de corais de profundidade. Desta maneira, visando não só apenas a proteção dos ecossistemas coralíneos de profundidade, mas também a sustentabilidade econômica da pesca, é recomendada a criação de áreas de exclusão da pesca demersal em locais com ocorrência de Scleractinia azooxantelados.

New Polygordiidae (Polychaeta) from the Australian region

The interstitial polychaete family Polygordiidae is recorded from Australia for the first time, based on two new species: Polygordius arafura sp. nov. from continental shelf depths in the Arafura Sea, northern Australia, and Polygordius kiarama sp. nov. from the continental shelf and slope off southeastern Australia. Polygordius kiarama sp. nov., found at slope depths up to 1650 m, is the deepest record to date for the family, which has previously been recorded from intertidal habitats, shallow coastal waters and continental shelf depths.

Growth and size-structure of Stegophiura sp. (Echinodermata: Ophiuroidea) on the continental slope off central Chile: a comparison between cold seep and non-seep sites

The growth and size-structure of the bathyal ophiuroid brittle star, Stegophiura sp., were analysed from skeletal growth bands and disc diameter frequencies. Specimens were collected in trawl samples taken on the continental slope off central Chile (~36°S) at two sites within the recently discovered Concepción Methane Seep Area (CMSA) and at two control non-seep sites. Growth bands were measured as radii of vertebral ossicles from scanning electron microscope (SEM) micrographs and used to provide size-at-age data. The von Bertalanffy and the Gompertz growth models provided good fit to size-at-age data. The size-structure distributions observed in the study area suggest that small-bodied (<10 mm disc diameter) individuals of Stegophiura sp. are more abundant near seep sites, probably attracted there by the presence of methane-derived authigenic carbonates, which provide a preferred habitat for ophiuroids and benthic fauna in general. Furthermore, size-at-age data from measurements of the ossicle growth bands indicate relatively rapid growth of Stegophiura sp. populations at seep sites. Assuming that the growth rings are annual, the maximum Stegophiura sp. age was estimated to be 15 years. The growth performance of this species falls within the range of values reported for sub-Antarctic and bathyal species.

Aspects of the Reproductive Biology of the SkateFenestraja plutonia(Garman) off North Carolina

Fenestraja plutonia is an abundant member of the slope community in the western North Atlantic, occurring at depths of 293-1042 m. Aspects of the reproductive biology of F. plutonia were examined for specimens collected off North Carolina, in the summer-fall of 2001, 2002, and 2006. Male-to-female sex ratios were not significantly different from 1:1. The smallest mature male was 215 mm TL, and the smallest mature female was 230 mm TL. Length at 50% maturity was estimated at 231 mm TL for females and 233 mm TL for males, 89 and 90% of maximum TL, respectively. Deposited egg cases (n = 107; six containing embryos), three egg-bearing females, and 11 newly hatched juveniles were collected. It appears that the upper slope off Cape Lookout, NC, at the northern end of the species range, constitutes both an egg-laying area and possibly a nursery area for this species.

The distribution of megabenthic, invertebrate epifauna in the Balearic Basin (western Mediterranean) between 400 and 2300 m: Environmental gradients influencing assemblages composition and biomass trends

The distribution of megabenthic epifauna (invertebrates) in the Balearic Basin (western Mediterranean) has been analyzed at depths between 427 and 2265 m after compiling samplings performed in 1985–1992 and 2007–2008 with an OTSB-14 bottom trawl. 84 epibenthic taxa of invertebrates (excluded decapod crustaceans) were collected. Epibenthic assemblages were organized in five groups (n-MDS analyses) as a function of increasing depth: upper slope assemblage, U, hauls between 427 and 660 m; middle slope assemblages M1 and M2, hauls between 663–876 m and 864–1412 m, respectively; lower slope assemblages L1 and L2, hauls between 1488–1789 m and 1798–2265 m, respectively). We found significant differences in assemblage composition between all depth-adjacent pairs of groups. Trends in the distribution of biomass vs. depth and within assemblages varied when hauls taken over insular were compared to those over mainland slopes. Over insular slopes we found (n-MDS) only four distinct depth assemblages, with significant differences between all depth-adjacent group pairs, except between L1 and L2. Over the mainland slope, two peaks of biomass situated at U (427–660 m) and at L1 (1488–1789 m) were clearly identified, attributable to the echinoid Brissopsis lyrifera and holothurian Molpadia musculus at U and to the synallactid holothurian Mesothuria intestinalis at L1. The distribution of biomass vs. depth on insular slopes did not follow this pattern, showing no significant biomass peak below 1000 m and a total biomass an order of magnitude lower than adjacent to the mainland. After compiling available environmental data over the mainland slope off Barcelona, we found coincidence between the peak biomass of Mesothuria intestinalis and: i) a significant increase of labile OM (%OrgC, C/N, hydrolizable aminoacids–EHAA, and the EHAA/THAA-total hydrolizable aminoacids-ratio) over 1600 m; and ii) an increase of turbidity and T at 1500–1600 m in February 2008. We suggest that such OM inputs must likely be associated to the formation of nepheloid layers close to submarine canyons, probably associated with oceanographic processes in deep water masses in the area. This would explain why aggregations of M. intestinalis were linked to the mainland part of the Balearic basin, with highest densities located south of canyons. If hotspots of biomass as cited here for M. intestinalis are regulated by factors such as river inputs, both natural climatic changes (e.g. changes in rainfall regimes) and human impact (e.g. river damming) may affect deep-Mediterranean communities below 1000 m.

The initiation of sliding on the mid Norway margin in the Møre Basin

The continental slope off Mid Norway is one of the most unstable continental slopes in the world, being the locus for several large mass movements including the important Storegga Slide. Comparatively little is known about the initiation of slope instability in this region. Here 2D and 3D seismic reflection data are used to describe the two earliest slides to occur in the Neogene of the Møre Basin in order to aid understanding of the initiation of slope instability. The first slide was sourced from the continental slope and occurred sometime between 3.6 Ma and the time of deposition of sediments that failed as the second slide. The second slide was also sourced from the continental slope, and the sediments that failed in this slide were deposited before 1.8 Ma. This second slide is larger in volume than the Storegga Slide. The deposition of the package of sediments that failed in the two slides coincided with the deposition of a large contourite mound in the north of the basin. A polygonal fault system in this basin ceased activity at the time of arrest of an opal A/opal CT boundary. This arrest is linked temporally to the onset of slope instability. The onset and continuation of slope instability on this margin are also linked with a steepening continental slope, due to tilting and subsidence of the margin.

Application of self-absorption correction method in gamma spectroscopy for210Pb and137Cs sediment chronology on the continental slope off NW Africa

The uppermost 50cm of the high resolution core GeoB9501-4 from the continental slope off NW Africa has been used for improving routine technique of 210 Pb and 137 Cs sediment chronology in the Radioactivity measurement laboratory of the Bremen University. The experimental requirements for 210 Pb and 137 Cs determination were non-destructive analysis of wet sediment samples in cylindrical containers with different heights, unknown elemental composition and density. The method used in this study to deal with self attenuation is applying efficiencies calculated using the LabSOCS TM , Genie 2000 software calibration tool, validated by self-absorption test measurements of different materials with known composition. A mean sedimentation rate of 0.49cm · yr −1 was obtained from the investigated core using the CRS chronological model. This means a relatively increased recent sedimentation rate comparing to an average sedimentation rate at higher depths of an associated gravity core estimated to 0.15cm · yr −1 by 14 C chronology. A further increase of the sedimentation rate was observed in the uppermost part of the studied core (up to 0.90cm · yr −1 ). Life in the semiarid Sahel belt of tropical North Africa strongly depends on the availability of water and has been repeatedly affected by shifts to more arid climate. The most recent drought occurred in the early 1970's and 1980's, with partial recovery during the late 1990's. High resolution fluvial sediments off Senegal offer the opportunity to study the history of the Sahel drought and to assess its imprint on the composition of terrestrial materials deposited at the sea floor, if the material can be accurately dated on historical time scales.

Contribution to Understanding the Population Structure and Maturation of Illex argentinus (Castellanos, 1960): the Case of the Inner-shelf Spawning Groups in San Matias Gulf (Patagonia, Argentina)

Illex argentinus is known for spatiotemporally segregating into reproductive aggregations on the mid-continental shelf and slope off southern South America. In this study we found that the species also mates and spawns in San Matías Gulf, a coastal basin off northeastern Patagonia. Basing on the analysis of size and maturity structure of squids caught over a 28-month period in waters of the gulf, distinct demographic pulses were identified in the samples each year. Two of them were more consistent, one comprising small-sized individuals reaching full maturity in January to February (summer) and the other including larger individuals maturing between September and October/December (spring). Also, a less conspicuous group of mature individuals was observed in June/July (winter) of the last sampling year. So far, differences in the parameters of the size-at-maturity curves of these population components allow considering at least two stocks for management of I. argentinus in the gulf.

Abrupt changes of intermediate-water oxygen in the northwestern Pacific during the last 27 kyr

An oxygen minimum zone (OMZ) currently exists at intermediate water depths on the northern Japanese margin in the northwestern Pacific. The OMZ results largely from a combination of high surface–water productivity and poor ventilation of intermediate waters. We investigated the late Quaternary history (last 27 kyr) of the intensity of this OMZ using changes in benthic foraminiferal carbon isotopes and assemblages in a sediment core taken on the continental slope off Shimokita Peninsula, northern Japan, at a water depth of 975 m. The core was located well within the region of the present-day OMZ and high surface–water productivity. The benthic foraminiferal δ13C values, which indicate millennial-scale fluctuations of nutrient contents at the sediment–water interface, were 0.48‰ lower during the last glacial maximum (LGM) than during the late Holocene. These results do not indicate the formation of glacial intermediate waters of subarctic Pacific origin, but rather the large contribution of high-nutrient water masses such as the Antarctic Intermediate Water, implying that the regional circulation pattern during the LGM was similar to that of modern times. Benthic foraminiferal assemblages underwent major changes in response to changes in dissolved oxygen concentrations in ocean floor sediments. The lowest oxygen and highest nutrient conditions, marked by dysoxic taxa and negative values of benthic foraminiferal δ13C, occurred during the Bolling/Allerod (B/A) and Pre-Boreal warming events. Dysoxic conditions in this region during these intervals were possibly caused by high surface–water productivity at times of reduced intermediate–water ventilation in the northwestern Pacific. The benthic assemblages show dysoxic events on approx. 100- to 200-year cycles during the B/A, reflecting centennial-scale productivity changes related to freshwater cycles and surface–water circulation in the North Pacific.

Impact of melting of the Laurentide Ice Sheet on sediments from the upper continental slope off southeastern Canada: evidence from Sm–Nd isotopesThis article is one of a series of papers published in this Special Issue on the themePolar Climate Stability Network.

We present new Sm–Nd isotope data for sediments from a core located on the continental slope of the St. Pierre Bank of Canada’s east coast. The Nd analyses indicate that the sediments were derived from two principal sources: the North American Shield that yields an average early Proterozoic isotopic signature and a younger Proterozoic signature attributed to Appalachian crustal sources. The Appalachian-sourced sediments predominated during the last glacial maximum (LGM) and were associated with low sedimentation rates (<30 cm/ka), with the exception of a strong North American Shield signature present in a detrital carbonate layer that corresponds to Heinrich Layer 1 (H1). The dominance of the Appalachian signature decreased subsequent to H1. The Appalachian signatures closely follow the distribution of sediments interpreted as locally derived glacial tills, while the North American Shield signatures follow the distribution of hemipelagic mud that was likely deposited by the Labrador Current. The Nd data are consistent with the persistence of the Wisconsinan Ice Sheet coverage of Newfoundland and the Grand Banks after the LGM, although the coverage began to wane prior to 12.5 ka as evidenced by the increasing influence of the Labrador Current. However, an increase in the Appalachian isotope signature at the close of the Younger Dryas event likely indicates the final melting of the ice sheet covering the Grand Banks and the Avalon Peninsula, and the initiation of the Labrador Current’s modern circulation pathway.

Sahel megadroughts triggered by glacial slowdowns of Atlantic meridional overturning

The influence of the large‐scale ocean circulation on Sahel rainfall is elusive because of the shortness of the observational record. We reconstructed the history of eolian and fluvial sedimentation on the continental slope off Senegal during the past 57,000 years. Our data show that abrupt onsets of arid conditions in the West African Sahel were linked to cold North Atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with Heinrich Stadials. Climate modeling suggests that this drying is induced by a southward shift of the West African monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric African Easterly Jet.

Seasonal variability in Atlantic Water off Spitsbergen

A combination of 2-year-long mooring-based measurements and snapshot conductivity–temperature–depth (CTD) observations at the continental slope off Spitsbergen (81°30′N, 31°00′E) is used to demonstrate a significant hydrographic seasonal signal in Atlantic Water (AW) that propagates along the Eurasian continental slope in the Arctic Ocean. At the mooring position this seasonal signal dominates, contributing up to 50% of the total variance. Annual temperature maximum in the upper ocean (above 215 m) is reached in mid-November, when the ocean in the area is normally covered by ice. Distinct division into ‘summer’ (warmer and saltier) and ‘winter’ (colder and fresher) AW types is revealed there. Estimated temperature difference between the ‘summer’ and ‘winter’ waters is 1.2 °C, which implies that the range of seasonal heat content variations is of the same order of magnitude as the mean local AW heat content, suggesting an important role of seasonal changes in the intensity of the upward heat flux from AW. Although the current meter observations are only 1-year long, they hint at a persistent, highly barotropic current with little or no seasonal signal attached.

LIVE BENTHIC FORAMINIFERAL ASSEMBLAGES AT THE PACIFIC CONTINENTAL MARGIN OF COSTA RICA AND NICARAGUA

Living (rose-Bengal-stained) foraminifera were investigated from the continental margin off the Pacific Coast of Costa Rica and Nicaragua. Assemblages from seven stations, including mounds and mud volcanoes, were compared in terms of foraminiferal density, distribution patterns, diversity and species composition and related to environmental factors (satellite chlorophyll a imagery, organic carbon content in the sediment, available oxygen data, particle grain sizes). Sediments from mud volcanoes and mounds did not show direct influence of seepage. Highest foraminiferal densities were found on the slope off Nicaragua. The lowest foraminiferal densities were found in the north off Costa Rica where the smooth Cocos Plate segment subducts beneath the Caribbean Plate. Intermediate values were counted in the southern investigated area, where the down-going plate has a rough topography. Observed foraminiferal densities did not always correspond to chlorophyll a imagery or measured organic carbon content in the sediment, suggesting a possible influence of time-limited food supply, lateral transport of sinking organic material and local variability in the investigated area. In total, 187 species were recognized, distributed across the seven stations, which all showed high diversity. Foraminiferal associations contained many Buliminida, pointing to low-oxygen concentrations at the sediment-water interface. Some taxa indicated a possible bathymetric or regional limitation. The assemblage composition varied among the stations to such a degree that no commonalities were identified, based on results from multivariate analysis. This was also the case for samples originating from mounds and mud volcanoes, which did not show any outstandingly different assemblages, meaning that no characteristic foraminiferal assemblage could be used to identify these areas. This mosaic-like distribution pointed to a large degree of habitat heterogeneity in the relatively small area; the habitat heterogeneity could explain the overall high diversity of benthic foraminifera in the region.

Redwood of the reef: growth and age of the giant barrel sponge Xestospongia muta in the Florida Keys

The growth of animals in most taxa has long been well described, but the phylum Porifera has remained a notable exception. The giant barrel sponge Xestospongia muta dominates Caribbean coral reef communities, where it is an important spatial competitor, increases habitat complexity, and filters seawater. It has been called the 'redwood of the reef' because of its size (often(1 m height and diameter) and presumed long life, but very little is known about its demography. Since 1997, we have estab- lished and monitored 12 permanent 16 m diameter circular transects on the reef slope off Key Largo, Florida, to study this important species. Over a 4.5-year interval, we mea- sured the volume of 104 tagged sponges using digital images to determine growth rates of X. muta. Five models were fit to the cubed root of initial and final volume esti- mates to determine which best described growth. Additional measurements of 33 sponges were taken over 6-month intervals to examine the relationship between the spongocoel, or inner-osculum space, and sponge size, and to examine short-term growth dynamics. Sponge volumes ranged from 24.05 to 80,281.67 cm 3 . Growth was variable, and specific growth rates decreased with increasing sponge size. The mean specific growth rate was 0.52 ± 0.65 year -1 , but sponges grew as fast or slow as 404 or 2% year -1 . Negative growth rates occurred over short temporal scales and growth varied seasonally, significantly faster during the summer. No differences in specific growth rate were found between transects at three different depths (15, 20, 30 m) or at two different reef sites. Spongocoel volume was positively allometric with increasing sponge size and scaling between the vertical and horizontal dimensions of the sponge indicated that morphology changes from a frustum of a cone to cylindrical as volume increases. Growth of X. muta was best described by the general von Bertalanffy and Tanaka growth curves. The largest sponge within our transects (1.23 9 0.98 m height 9 diameter) was estimated to be 127 years old. Although age extra- polations for very large sponges are subject to more error, the largest sponges on Caribbean reefs may be in excess of 2,300 years, placing X. muta among the longest-lived animals on earth.

Encounter of lithodid crab Paralomis birsteini on the continental slope off Antarctica, sampled by ROV

A population of stone crab (Lithodidae) was encountered on the continental slope off Antarctica in the Bellingshausen Sea between 1,123 and 1,304 m water depths using the ROV-Isis during leg 166 of the RV James Clark Ross, in January 2007. Specimens were video recorded and one specimen was retrieved by ROV for morphological and molecular identification. Based on morphology and molecular data from the mitochondrial COI gene, this specimen identified as P. birsteini, Macpherson, 1988a. The significance of the molecular data and their implications for biogeography and evolution of lithodids in the Southern Ocean are briefly discussed.

Horizontal distribution patterns in Arctic deep-sea macrobenthic communities

Horizontal distribution patterns of macrobenthos were studied based on the material collected at the deep-sea long-term observatory HAUSGARTEN in Fram Strait, west of Spitsbergen (79°N), during the R.V. Polarstern expedition ARK XIX/3c in July–August 2003. Macrofauna was obtained with a giant box corer at water depths of about 2500–2600 m. Samples were arranged using a hierarchical approach to analyze benthic fauna distribution at different scales. Three stations were distributed along the 26 km transect. Three cores (0.25 m 2) were taken at each station. Five subcores (156.25 cm 2) were taken from each core. Both qualitative and quantitative methods of statistical analysis showed that all samples belong to one benthic community dominated by three species, Tetractinomorpha gen.sp. A, Myriochele heeri, and Galathowenia fragilis. Total biomasses varied from 2.31 to 6.41 g ww m −2 and densities ranged from 1976 to 3254 ind. m −2. Multivariate analysis showed the division of all samples into two distinct groups (species assemblages) on the core and subcore levels. These assemblages occupied an area several kilometers across, and differed from each other. The second level of heterogeneity occurs between cores and subcores of assemblage B and reflects variations in the abundance of sponge species Tetractinomorpha gen. sp. A. The size of these small patches appears to be about 150 cm 2. The hierarchical organization of benthic macrofauna on the continental slope off Spitsbergen includes at least three levels: communities, which replace each other along the depth gradient, species assemblages, which make up the orthogonal inner mosaics in each vertical zone, and patches of certain species, which form the lowest level of the hierarchy.