Megafaunal Assemblages Research Articles

New U/Th ages for Pleistocene megafauna deposits of southeastern Queensland, Australia

Arguments over the extinction of Pleistocene megafauna have become particularly polarised in recent years. Causes for the extinctions are widely debated with climate change, human hunting and/or habitat modification, or a combination of those factors, being the dominant hypotheses. However, a lack of a spatially constrained chronology for many megafauna renders most hypotheses difficult to test. Here, we present several new U/Th dates for a series of previously undated, megafauna-bearing localities from southeastern Queensland, Australia. The sites were previously used to argue for or against various megafauna extinction hypotheses, and are the type localities for two now-extinct Pleistocene marsupials (including the giant koala, Phascolarctos stirtoni). The new dating allows the deposits to be placed in a spatially- and temporally constrained context relevant to the understanding of Australian megafaunal extinctions. The results indicate that The Joint (Texas Caves) megafaunal assemblage is middle Pleistocene or older (>292 ky); the Cement Mills (Gore) megafaunal assemblage is late Pleistocene or older (>53 ky); and the Russenden Cave Bone Chamber (Texas Caves) megafaunal assemblage is late Pleistocene (∼55 ky). Importantly, the new results broadly show that the sites date prior to the hypothesised megafaunal extinction ‘window’ (i.e., ∼30–50 ky), and therefore, cannot be used to argue exclusively for or against human/climate change extinction models, without first exploring their palaeoecological significance on wider temporal and spatial scales.

Strategies, methods, and technologies adopted on the R.V. G.O. Sars MAR-ECO expedition to the Mid-Atlantic Ridge in 2004

Abstract The MAR-ECO project aimed to gather information on mid-ocean ridge macro- and megafaunal assemblages and their distribution patterns in relation to the abiotic environment, and the target area extended from Iceland to the Azores, comprising waters associated with the Mid-Atlantic Ridge. Strategies and methods adopted on the 2004 international expedition on the R.V. G.O. Sars and M.S. Loran were selected in order to maximise data and sample collection in all pelagic and benthic habitats to a maximum depth of 3500 m, spanning the organism size range from mm to metres. The approach selected was to combine (1) Continuous sampling along the ship's track; (2) Point observations using a pre-defined set of samplers at pre-determined sites; and (3) Opportunistic sampling to study particular phenomena or carry out exceptional tasks. A wide range of nets and mid-water and bottom trawls were mobilised in order to collect biological samples. Hull-mounted, lowered and towed optical and acoustical instruments collected data and images. Two remotely operated vehicles (ROVs) were used for pelagic and demersal studies, and moored echosounders and cameras on benthic landers collected vessel-independent information. Observation of whales and seabirds were made from a custom-built observation area on top of the wheelhouse. Using a range of technologies from the same platform efficiently provided comprehensive results and enhanced the potential for new discoveries at the organism, community, and ecosystem levels.

Spatio-temporal variations in deep-sea demersal communities off the Balearic Islands (western Mediterranean)

The spatial and temporal variations of deep-sea megafaunal assemblages from the western Mediterranean are analysed in the present paper. The assemblages from two locations of the Balearic Islands situated 120 km apart were compared using data collected seasonally on a bathymetric stratum covering the 150–750 m depth range during six bottom-trawl surveys. The assemblage structure, in terms of species composition, species dominance and population sizes, was differentially affected by the spatio-temporal variables analysed (depth, location and fishing period). Although depth was the main factor determining the assemblage composition, the differences obtained between the two locations were also relevant. On the upper slope these between-location differences in the dynamics of megafaunal assemblages were found to be related to the effect of fishing exploitation. Population size-based metrics and biomass spectra were good predictors of meso-scale fishing effects, and were mainly reflected by elasmobranchs and demersal teleosts. Nevertheless, the effects of fishing depended on the species considered. Two dominant large-sized fish species found on the upper slope in both localities, Galeus melastomus and Phycis blennoides, had higher biomass values associated with lower fishing effort. Although the mean body weight (MBW) of both species and also the mean maximum body weight (MMBW) of G. melastomus agreed with this pattern, the P. blennoides MMBW did not. This last case could be indicative of natural size-trends such as the bigger–deeper phenomenon which refers to the displacement of large individuals towards the deeper limit of their bathymetric distribution, beyond the maximum depth sampled in this study for this species. By contrast, the target species of the upper slope fishery, the red shrimp Aristeus antennatus, was not negatively affected by the direct impact of fishing activity and other environmental factors, such as the presence of specific water masses could also be important.

Depth-related changes in the arctic epibenthic megafaunal assemblages of Kangerdlugssuaq, East Greenland

The effects of depth-related differences in environmental factors (pressure, hydrography, habitat and disturbance) on the benthic megafauna at the mouth of Kangerdlugssuaq Fjord in Arctic Greenland were investigated using a towed camera platform and autonomous underwater vehicle photographs. Large reductions in faunal density (60,132 to 1881 individuals ha−1) and increases in diversity (H′=0.93–2.54), through increases in richness (ES(220)=7.6–18.8) and reductions in dominance (Berger–Parker index=0.77–0.38) were found between 270 and 720 m water depth. Assemblages were separated into distinct shallow, intermediate and deep faunas by multivariate community analysis. In the shallower sites there were high levels of iceberg disturbance, directly reducing diversity as well as creating a complex, patchy environment inhabited by high densities of mobile suspension-feeding epifauna. In the deeper areas there was small-scale disturbance from the deposition of drop stones, but at a relatively low frequency and magnitude, which allowed increased species diversity. Proportions of deposit-feeding epifaunal and infaunal taxa rose with depth, as indicated by an increase with depth in faunal traces. Decreases in faunal density probably resulted from decreased food supply with depth.

Depth-related changes to density, diversity and structure of benthic megafaunal assemblages in the Fimbul ice shelf region, Weddell Sea, Antarctica

The depth-related patterns in the benthic megafauna of the NE Weddell Sea shelf at the edge of the Fimbul Ice Shelf were investigated at seven sites using towed camera platform photographs. Megafaunal density decreased with depth from 77,939 ha−1 at 245 m to 8,895 ha−1 at 510 m. While diversity was variable, with H′ ranging between 1.34 and 2.28, there were no depth related patterns. Multivariate analyses revealed two distinct assemblages; a shallow assemblage with dense patches of suspension feeders in undisturbed areas and a deep assemblage where these were not present. Disturbance from icebergs explained many observed patterns in faunal distribution. In shallow waters probable effects of disturbance were observed as changes in successional stages; in deeper waters changes in habitat as a result of past disturbance explained faunal distributions. In deeper areas ice ploughing created a mosaic landscape of fine and coarse sediments. Total megafaunal density was highest in areas of coarse sediment (up to 2.9 higher than in finer sediment areas) but diversity was highest in intermediate areas (H′ = 2.35).

Habitat Associations in Gastropod Species at East Pacific Rise Hydrothermal Vents (9°50′N)

At deep-sea hydrothermal vents on the East Pacific Rise (9 degrees 50'N), distinct megafaunal assemblages are positioned along strong thermal and chemical gradients. We investigated the distribution of gastropod species to determine whether they associate with specific megafaunal zones and to determine the thermal boundaries of their habitats. Gastropods colonized a series of basalt blocks that were placed into three different zones characterized by vestimentiferan tubeworms, bivalves, and suspension-feeders, respectively. Additional gastropods were collected on selected blocks from higher temperature vestimentiferan habitat and from grab samples of alvinellid polychaetes. On the blocks, gastropod species clustered into a "Cool" group (Clypeosectus delectus, Eulepetopsis vitrea, Gorgoleptis spiralis, and Lepetodrilus ovalis) whose species tended to be most abundant in the suspension-feeder zone, and a "Warm" group (Lepetodrilus cristatus, L. elevatus, L. pustulosus, and Cyathermia naticoides) whose species all were significantly more abundant in the vestimentiferan zone than elsewhere. The temperature ranges of Cool species were generally lower than the ranges of Warm ones, although both groups were present at 3 to 6 degrees C; also present was Bathymargarites symplector, which clustered with neither group. Three additional species, Rhynchopelta concentrica, Neomphalus fretterae, and Nodopelta rigneae, co-occurred with Warm-group species on selected blocks from hotter habitats. Although a few species were found only in alvinellid collections, most species were not exclusive to a specific megafaunal zone. We propose that species in the Cool and Warm groups occupy specific microhabitats that are present in more than one zone.

Anthropogenic disturbance of deep-sea megabenthic assemblages: a study with remotely operated vehicles in the Faroe-Shetland Channel, NE Atlantic

The effects of local-scale anthropogenic disturbance from active drilling platforms on epibenthic megafaunal abundance, diversity and assemblage pattern were examined in two West of Shetland hydrocarbon fields at 420 m and 508 m water depth. These areas were selected to include a range of disturbance regimes and contrasting faunal assemblages associated with different temperature regimes. Remotely Operated Vehicle (ROV) video provided high-resolution megafaunal abundance and diversity data, which were related to the extent of visible disturbance from drilling spoil. These data, in conjunction with a study deeper in the Faroe-Shetland Channel, have allowed comparison of the effects of disturbance on megabenthos across a range of sites. Disturbance to megafaunal assemblages was found to be high within 50 m of the source of drill spoil and in areas where spoil was clearly visible on the seabed, with depressed abundances (Foinaven 1900 individuals ha-1; Schiehallion 2178 individuals ha-1) and diversity (H´ = 1.75 Foinaven; 1.12 Schiehallion) as a result of smothering effects. These effects extended to around 100 m from the source of disturbance, although this was variable, particularly with current regime and nature of drilling activity. Further from the source of disturbance, megafaunal assemblages became more typical of the background area with increased diversity (H´ = 2.02 Foinaven; 1.77 Schiehallion) and abundance (Foinaven 16484 individuals ha-1; Schiehallion 5477 individuals ha-1). Visible effects on megafaunal assemblages as a result of seabed drilling were limited in extent although assemblage responses were complex, being controlled by differing effects to individual species often based on their motility.

Matching biological traits to environmental conditions in marine benthic ecosystems

The effects of variability in environmental conditions on species composition in benthic ecosystems are well established, but relatively little is known about how environmental variability relates to ecosystem functioning. Benthic invertebrate assemblages are heavily involved in the maintenance of ecological processes and investigation of the biological characteristics (traits) expressed in these assemblages can provide information about some aspects of functioning. The aim of this study was to establish and explore relationships between environmental variability and biological traits expressed in megafauna assemblages in two UK regions. Patterns of trait composition were matched to environmental conditions and subsets of variables best describing these patterns determined. The nature of the relationships were subsequently examined at two separate scales, both between and within the regions studied. Over the whole area, some traits related to size, longevity, reproduction, mobility, flexibility, feeding method, sociability and living habit were negatively correlated with salinity, sea surface temperature, annual temperature range and the level of fishing effort, and positively associated with fish taxon richness and shell content of the substratum. Between the two regions, reductions in temperature range and shell content were associated with infrequent relative occurrences of short-lived, moderately mobile, flexible, solitary, opportunistic, permanent-burrow dwelling fauna and those exhibiting reproductive strategies based on benthic development. Relationships between some traits and environmental conditions diverged within the two regions, with increases in fishing effort and shell content of the substratum being associated with low frequencies of occurrence of moderately mobile and moderately to highly flexible fauna within one region, but high frequencies in the other. These changes in trait composition have implications for ecosystem processes, with, for example, reductions in permanent-burrow dwellers within one of the regions potentially compromising the ability of the assemblages to process and store chemicals and waste products. However, the connections between environmental conditions and trait composition are complex and incorporate many factors. Experimental investigations will be necessary to determine the extent and consequences of these important relationships.

Megafauna associated with assemblages of deep-water gorgonian corals in Northeast Channel, off Nova Scotia, Canada

The distribution and abundance of benthic megafauna in areas known to be inhabited by dense gorgonian coral assemblages were examined at Northeast Channel, off Nova Scotia, Canada, in August 2001. Using a remotely operated vehicle, 1–5 video transects during each of 1–2 dives at each of four sites (Rips, Middle Canyon, Hell Hole West and Hell Hole East) were conducted. The relationships in the structure of biological assemblages at three spatial scales: within transects (10s of metres); between dive locations (100s of metres); and among sites (10s to 100s of kilometres) were explored. The most abundant epibenthic taxa included the gorgonians Primnoa resedaeformis and Paragorgia arborea, several suspension feeders (Actinauge verrilli, Bolocera tudiae, an unidentified anemone and encrusting sponge, Ophiacantha abyssicola), the deposit feeder Porania pulvillus insignus and the predatory Solaster endeca. The basket star Gorgonocephalus arcticus was present only on colonies of Paragorgia arborea. Despite large variability in abundance and assemblage composition among transects and dive locations, clear patterns were observed among sites. Mean abundance of most cnidarians and echinoderms was greatest at Hell Hole West. No gorgonians were found at Hell Hole East. The encrusting sponge was most abundant at the Rips and least abundant at Hell Hole East. Cluster analysis and multidimensional scaling (MDS) indicated that, when abundance was averaged across transects for each dive, the megafaunal assemblages fall into groups of dives that separated by site. These differences among sites are most likely related to variability in the physical environment. The epibenthic megafaunal assemblages were as diverse in the presence as in the absence of gorgonian corals, at least at the abundances that we observed. However, the apparent low recruitment and abundance, combined with small population size make these assemblages particularly vulnerable to perturbations.

A Silurian Cold-Seep Ecosystem From the Middle Atlas, Morocco

Abstract Geological and paleobiological attributes described in a carbonate unit from the upper Silurian of the Middle Atlas (Morocco) are interpreted as the result of chemosynthetic processes fueled by fluid seepage. These attributes include: the presence of authigenic carbonate accumulation embedded in siliciclastic rocks; tightly packed, monospecific megafaunal assemblages (atrypid brachiopods); microbial-derived products; precipitation of bio-induced minerals (especially hematite); and seep-derived carbonate phases. Evidence of in-situ growth of the dense brachiopod communities is that their shells are all articulated, and show a complete range of growth sizes. Products of microbial activity are shared with other fossil seep deposits and include clotted micrite concentrations, crusts, and laminated structures, microtufts, biofilms, and endolithic filaments. The best-developed microbial features were recovered in reddish mudstone beds below and within the brachiopod concentrations, where they consist o...

Identification of patch structure within marine benthic landscapes using a remotely operated vehicle

The spatial scale of megafaunal assemblage variation in apparently homogeneous subtidal sediment was investigated using quantitative observations from a remotely operated vehicle (ROV). Quantitative abundance estimates of surface-dwelling megafauna and biotic sediment features associated with burrowing megafauna were derived from video images using the Automated Benthic Image-Scaling System (ABISS), a novel method of applying scale to images collected by ROVs. Spatially referenced images were collected with a maximum sample separation of 400 m within a broader area of apparently homogeneous sediment in Plymouth Sound (Devon, UK) during May 2000 and March 2001. Rank-correlograms were constructed to examine the extent and form of the megafaunal spatial structure. The megafaunal assemblage was neither uniformly distributed nor temporally stable. A hierarchy of spatial structure was detected within the megafaunal assemblage, whereby patches with minimum radius between 123 and 163 m were nested within patches up to 400-m radius. The approach described in this paper offers ways forward to address how variation of megafaunal spatial structure affects macrofaunal assemblage structure and to discuss the application of remote imaging to map and predict the conservation value of subtidal soft sediments.

Feeding guilds of western Mediterranean demersal fish and crustaceans: an analysis based in a spring survey

The MEDITS-99 sampling was performed along all the Iberian Peninsula coasts of the western Mediterranean (from the Alborán Sea to Cape Creus) in a space-scale of 1000 Km N-S, at depths ranging between 27-790 m. Fish and decapod crustaceans were dominant in the megafaunal compartment sampled by trawling. Based on both the fish and the decapod crustacean compositions, a comparison of trophic guilds has been attempted, with fish and decapods classified as: 1) migrator macroplankton feeders (mM), 2) non-migrator macroplankton feeders (nmM), 3) nektobenthos-suprabenthos feeders (NS), 4) epibenthos feeders (Epib), 5) large detritus-scavengers (Sca), 6) infaunal feeders (Inf), 7) deposit feeders (Dep) and 8) small detritivorous feeders (Det). Multivariate techniques showed the following differences in the trophodynamics of the megafaunal assemblages along the coasts of the Iberian Peninsula: 1) crustaceans (mainly decapods) have different trophic structures on the shelf and on the slope; 2) on the slope, fish exhibited more clear changes as a function of the geographical gradient than crustaceans; and 3) trophodynamics of bathyal fish showed some geographic variations between the Alborán Sea, the Catalano-Balearic Basin, and the Algerian Basin (Vera Gulf and Alicante sectors), with a progressive north-south increase in planktophagous species.

Electron spin resonance dating of the fossil deposits in the Naracoorte Caves, South Australia

The caves near Naracoorte, South Australia, contain one of the richest and most diverse fossil faunal assemblages on the Australian continent. Three sites were selected for electron spin resonance (ESR) dating because clastic, fossiliferous sediments were sandwiched between speleothem layers. This allows independent age control by highly precise thermal ionization mass-spectrometry (TIMS) U-series dating. We find that all ESR results agree within the constraints given by the U-series dates, and allow further refinement of the age of the fauna analysed, indicating that most of the fauna in the large Victoria Cave Fossil Chamber is twice as old as reported previously. Our dating results, spanning from 280 to 500 ka for the Fossil Chamber, Victoria Cave, to about 125 ka for the Grant Hall, Victoria Cave, and 170 to 280 ka for the Fossil Chamber, Cathedral Cave, indicate little change, if any, in the megafaunal assemblage from the early Middle to the early Late Pleistocene. This changed dramatically after the last interglacial, when a large proportion of the megafauna suddenly disappeared. Copyright © 2001 John Wiley & Sons, Ltd.

Age of the Lancefield megafauna: A reappraisal

The Lancefield megafauna site is located on the southwest edge of the small town of Lancefield, 70 km NNE of Melbourne. The site is located in a swamp, a depression (possibly formed by a collapsed lava tunnel) which is almost surrounded by weathered Pliocene basalts which have formed a laterite cap. A natural spring flow under this cap emerges at the swamp and the water then drains into Deep Creek, a tributary of the Maribyrnong River. Three fossil megafaunal assemblages occur at Lancefield. The original discovery of 1843, now known as the Mayne Site, was the focus of investigations in the nineteenth-century and again in 1991 (van Huet 1993). The South Site, found in 1983, has been excavated three times since the early 1980s, most recently by van Huet in 1991 (van Huet 1994). The Classic Site was discovered in 1973 and was the focus of major investigations in 1975-76 (Horton 1976; Ladd 1976; Gillespie et al. 1978; Horton and Samuel 1978). Â

Distribution and abundance of epibenthic megafauna at a long time-series station in the abyssal northeast Pacific

Abundance and dispersion of epibenthic megafauna were examined at an abyssal site (4100 m depth) in the northeast Pacific (Sta. M, 34°50'N, 123°00'W). Photogrammetric techniques and line-transect theory were used to analyze photographs from nine towed camera-sled transects made on six cruises between June 1990 and October 1991. The megafaunal assemblage was dominated numerically by the tube-dwelling polychaete Paradiopatra sp. and echinoderms, representing 26–48% and 24–41 % of the total, respectively. Megafaunal densities were remarkably similar among the nine transects, ranging from 26,594 to 39,913 individuals 10 −4m −2. While the overall assemblages in the nine transects were ⩽80% similar, based on pairwise comparisons, the relative contribution of each faunal category varied significantly between transects; densities of individual species from pairs of synoptic transects were significantly different ( p < 0.05) in 43 of 69 cases. Analysis of dispersion was limited by small sample sizes, but overall the distributions of these organisms either did not deviate from random or tended toward aggregation. The dispersion of individual taxa often was highly variable within a single transect and among transects, indicating a high level of spatial heterogeneity. Spatial heterogeneity in density and dispersion overwhelmed any temporal variation that might exist, at least on short timescales (<1.5 years). These results illustrate how variable the benthos can be, even within a relatively small area, and that large areas need to be surveyed to adequately describe megafaunal community structure.

The classification and structure of megafaunal assemblages in the Venezuela Basin, Caribbean Sea

Data from 23 benthic trawls collected from the Venezuela Basin (3411-5062 m water depth) indicate that megafauna are less abundant than in basins of similar depths in the Atlantic and are segregated by sedimentary province. Taxonomic assemblages, in terms of abundance and biomass, from three sites coincide with distinctions of sedimentary characteristics among the pelagic, hemipelagic and turbidite sedimentary provinces. Mollusks, decapods and fishes are most abundant in trawls collected from the pelagic and hemipelagic provinces and anemones and holothurians are most abundant in trawls collected from the turbidite province. Sponges dominate the biomass of fauna in trawls collected in the turbidite and hemipelagic provinces and fishes dominate the biomass of trawls collected in the pelagic province. Several biological and physical aspects of the basin contribute to the segregation of the megafauna into distinct communities. Sponges and anthropogenic debris (coal, coal clinker and tar balls) reaching the sea floor create a habitat that is exploited by sessile suspension feeders requiring a hard substrate. Filter-feeding anemones attached to debris occur in such abundance that it elevates the importance of suspension feeders and depresses species diversity at the turbidite site. Biomass and average size of megafaunal deposit feeders in the basin decrease with decreasing amounts of organic carbon and nitrogen content of the sediment. Distribution and composition of filter-feeding megafaunal biomass in the Venezuela Basin are explained largely by proximity to sources of organic matter. Detrital carbonate may also play a role in controlling distribution and density of megafauna by diluting food resources in the sediments.

Bathymetric and Seasonal Patterns in the Sublittoral Megafauna off Central Chile

The sublittoral off central Chile represents a dynamic border separating an oxic surface equatorward current and an oxygen-poor poleward undercurrent. This investigation dealt with whether megafaunal assemblage structure and its temporal and bathymetric distribution were affected by this feature. The problem was approached by investigating the empirical relations between an assemblage index of abundance and physical factors of the environment. The megafauna off Conceptión Bay, central Chile (36°32′S) was thus sampled with an Agassiz trawl on eight cruises performed during 1991 and 1992 at three fixed stations (40, 64 and 96 m depth). Simultaneous reference samples of sea-water were taken to measure temperature, salinity, and dissolved oxygen. Descriptive assemblage attributes, diversity indices, and principal component analysis (PCA) for assemblage study were used. Moreover stepwise linear regression, with the first principal component of the specific abundance matrix as dependent variable was used to study relationships between temperature, salinity and dissolved oxygen and an assemblage of 23 species. Species richness, biomass and abundance decreased significantly with depth while diversity was highest in the intermediate depth station. Discontinuities were thus evident between the shallow, intermediate and deep stations. The grouping of samples in the plane formed by the first and second principal components showed a similar bathymetric discontinuity. In the Euclidian plane, a seasonal cycle of variation of the shallow sampling site was evident. Between 46 and 64 m depth lies a boundary separating different states of the same assemblage, the shallow seasonally variable and the deep constant. The intermediate station shares characteristics of both these stations reflecting a more variable environment. The overall bathymetric and the shallow seasonal patterns of variation were statistically linked to dissolved oxygen.

Spatial structure and seasonality of decapod crustacean populations on the northwestern Mediterranean slope

Two trawl surveys designed for geostatistical analysis were made in spring and fall 1991 on Nephrops norvegicus fishing grounds off Barcelona, Spain. High‐resolution geostatistical techniques‐a new tool for analyzing species assemblages‐were used to map and assess species abundances. Of the 43 decapod crustacean species collected, the spatial structures of the nine most abundant were analyzed and mapped by kriging. The maps of abundance drawn by kriging showed that the populations within the depth range of a species were not spread uniformly but were segregated in areas of high density. The locations of high concentration patches were generally mutually exclusive between pairs of species. The depth‐related zonation of the megafaunal assemblage studied was complemented by a strong alongshore spatial heterogeneity. The spatial structure revealed by the geostatistical analysis, namely local dominance by one or a few species and a spatial pattern of high‐density patches, made it difficult to predict the relative species composition at a given place, thus challenging the concept of a community of ecologically interacting decapod crustaceans over the continental slope. Local factors, such as canyon‐mediated hydrographic processes and sediment resuspension, helped account for the horizontal heterogeneity in the spatial distribution of decapod crustaceans.

Unusual megafaunal assemblages on the continental slope off Cape Hatteras

Abstract Megafaunal assemblages were studied in August–September 1992 using a towed camera sled along seven cross-isobath transects on the continental slope off Cape Hatteras. A total of 20,722 megafaunal organisms were observed on 10,918 m 2 of the sea floor between the depths of 157 and 1 924 m. These data were compared with data previously collected off Cape Hatteras in 1985 and at other locations along the eastern U.S. coast between 1981 and 1987. Megafaunal populations on the upper and lower slopes off Cape Hatteras were fouond to be similar, in terms of density and species composition, to those observed at the other locations. In contrast, megafaunal abundances were found to be elevated (0.88 and 2.65 individuals per m 2 during 1985 and 1992, respectively) on the middle slope off Cape Hatteras when compared to most other slope locations ( 2 ). These elevated abundances mainly reflect dense populations of three demersal fish, two eel pouts ( Lysenchelys verrilli and Lycodes atlanticus ) and the witch flounder Glyptocephalus cynoglossus , and a large anemone ( Actinauge verrilli ). These four species dominated the megafauna off Cape Hatteras, whereas they represented only a minor component of megafaunal populations found at other slope locations. Additionally, numerous tubes of the foraminiferan Bathysiphon filiformis were observed off Cape Hatteras, but not elsewhere. The high density of demersal fish found off Cape Hatteras appears to be related to the high densities of infaunal prey reported from this area. The high densities of A. verrilli and B. fuliformis may be related to the same factors responsible for the high infaunal densities, namely enhanced nutrient inputs in the form of fine particles. Extreme patchiness also was observed in the distributions of the middle slope taxa off Cape Hatteras. This patchiness may reflect the habitat heterogeneity of this exceptionally rugged slope and the sedentary nature of the organisms inhabiting it.

Microhabitat Utilization by the Megafaunal Assemblage at a Low Relief Outer Continental Shelf Site - Middle Atlantic Bight, USA

Direct underwater observations, using a manned submersible (May 1987) and remote operated vehicle (July and November 1988), were made of the small-scale distribution and microhabitat relationships of the megafaunal assemblage at a 55 m low relief outer continental shelf site (40 50'N, 70 Four microhabitat types were defined: flat sand with amphipod tubes, sand wave crests, shell (single valves and valve aggregates) and biogenic depressions. Microhabitat heterogeneity occurred on the scale of meters. Significant species-specific microhabitat relationships were found. Temperature mediated mesoscale shifts in megafaunal-microhabitat associations were found for several species.