1,721,056 research outputs found
Response of megabenthic assemblages to different scales of habitat heterogeneity on the Mauritanian slope
No full textThe topographically complex deep seabed on the Mauritanian slope, from 990 to 1460 m water depth, was imaged with video in an extensive quantitative survey of 17,199 m2 of seafloor using a Remote Operated Vehicle (ROV). This study investigated the influence of habitat heterogeneity at two scales on the megafaunal assemblages observed by ROV. Changes in megafaunal assemblages on the Mauritanian slope were assessed at a broad scale, within depth zones, and at a finer scale, in response to changes in local geomorphology associated with submarine landslides. Geomorphology was determined by classification of habitat parameters (slope, aspect, bathymetric position, curvature, fractal dimension and ruggedness) derived from an autonomous underwater vehicle-based multibeam bathymetry survey. Habitat parameters were classified by Iterative Self Organizing Clustering into six major geomorphological groups, four of which were assessed in the ROV video survey. A total of 29 megafaunal taxa were observed along the entire survey, with an overall average faunal density of 0.344 ind m−2. Megafaunal assemblage density, species richness and evenness varied significantly across the depth range of the survey in the most common geomorphological zone (sedimentary plains of low slope and complexity). Characteristic species inhabited the shallow areas (asteroid, ophiuroid, anemone, small macrourid), intermediate areas (Benthothuria funabris, black cerianthid, squat lobster) and deeper areas (the holothurians Enypniastes eximia and Elipidia echinata). Megafaunal density, species richness and evenness were not significantly different between geomorphogical groups within one depth zone (1300–1400 m). However, the steepest zone, on the edge of a major headwall feature, had four unique taxa (Parapagurus pilosimanus, a comatulid crinoid, a gorgonian and its associated ophiuroid)
Controls on the standing crop of benthic foraminifera at an oceanic scale
No full textCurrently there is very little basin-scale information on patterns of standing crop in marine organisms or their structuring forces. Understanding modern patterns and controls on foraminifera is particularly critical because of their abundance and importance in benthic systems as well as their role as palaeoceanographic proxies. Here, we examine for the first time basin-scale patterns and predictors of benthic foraminiferal standing crop from shelf to abyssal deep sea in the Atlantic Ocean and adjacent seas using a large database of 967 quantitative samples. Spatial regression analyses reveal that the flux of particulate organic matter (POC) is a major control on standing crop size across all depths investigated, with increasing food supply increasing foraminiferal standing crops. Other factors also play a role. Dissolved oxygen is significant at slope depths and negatively related to standing crop. Temperature and possibly salinity are significant factors in the abyss. Dissolved silicate was important and positively related to standing crop in shelf seas, potentially indicating the importance of the nature of the organic material available. This study demonstrates that productivity is important in describing foraminiferal standing crop at a basin scale, supporting the use of paleoceanographic proxies, but also demonstrates that other environmental variables are also likely important in controlling the standing crop and should be considered in reconstruction of Earth’s past marine environment
Megafaunal distribution and biodiversity in a heterogeneous landscape: the iceberg scoured Rockall Bank, NE Atlantic
Get PDFSpecies distributions are influenced by spatial structure in environmental factors, but the scales at which these dependencies occur and the effect of habitat patch diversity, connectivity and spatial arrangement have rarely been investigated in deep-sea settings. In this study, spatially-limited photographic transects collected from Rockall Bank, Northeast Atlantic, were combined with sidescan and multibeam sonar maps to model spatial patterns in species distribution and biodiversity. Sediment interpretation maps were created and canonical ordination techniques were used to examine relationships between fine-scale sediment characteristics extracted from the digital stills as well as landscape metrics describing the patch mosaic structure of the surrounding areas. Fine-scale sediment characteristics explained 45.1% and 63.8% of the variation in species composition and biodiversity (H′) respectively. This survey effectively captured variation in species distribution resulting from iceberg ploughmarks, occurring at a scale of < 50 m which would normally go undetected by traditional ship-based studies. Our study suggests that fine-scale environmental information is required to capture the spatial heterogeneity of complex seafloor areas in sufficient detail to model species distributions and biodiversity
The temporal and spatial distribution of krill (Meganyctiphanes norvegica) at the deep seabed of the Faroe–Shetland Channel, UK: A potential mechanism for rapid carbon flux to deep sea communities
No full textThe temporal and spatial distribution of Meganyctiphanes norvegica near the seabed (<5 m above the seafloor) was investigated using remotely operated vehicle (ROV) video footage from eight sites in the Faroe–Shetland Channel. Meganyctiphanes norvegica was most abundant near the seabed at 400–600 m depth, which corresponds to a temperature transitional region between shallower warmer water and deeper cold water. Densities of M. norvegica were significantly lower in the warm water, and no krill were detected at 900–1500 m depth in the cold water. Meganyctiphanes norvegica densities declined at night owing to daily vertical migrations. Time-series analysis showed higher krill densities at 06:00–09:00 and 18:00–21:00 at a depth of 400–480 m and at 12:00–15:00 at a depth of 600 m. A great reduction in krill abundance in winter was detected from both ROV surveys and continuous plankton recorder records. Meganyctiphanes norvegica was observed feeding on benthic particulate organic matter on the seafloor and being consumed by benthic and epibenthic predators. The maximum density of M. norvegica at 480 m depth was 596 ± 261 individuals m–3. This represents a standing stock of 12.8 ± 5.6 g C m–3 with an egestion rate of 0.63 ± 0.28 g C m–3 day–1. Meganyctiphanes norvegica potentially provides an important source of carbon for communities in the deep waters of the Faroe–Shetland Channel
Creating Landscape-Scale Maps of Coral Reef Cover for Marine Reserve Management from High-Resolution Multispectral Remote Sensing
No full textNew methods are needed for the study of coral reefs, as they are changing rapidly. Satellite remote sensing has become a common method for benthic mapping with advances in satellites and sensors and as methods are devised to account for atmospheric and water-column effects. Images from the QuickBird satellite have proven useful in reef mapping. Sand was distinguished from coral with an overall accuracy of 75% on the shallow reef off of the Caribbean island of Bonaire. Coral and sand had user accuracies of 50% and 90%, respectively. Increased samples of field-collected data would further increase the accuracies of such classifications
Changes in deep-water epibenthic megafaunal assemblages in relation to seabed slope on the Nigerian margin
Get PDFLocal-scale habitat heterogeneity associated with changes in slope is a ubiquitous feature of bathyal continental margins. The response of deep-sea species to high habitat heterogeneity is poorly known and slope can be used as a proxy for many important ecological variables, such as current flow, sedimentation and substratum type. This study determines how slope angle effects megafaunal species density and diversity at the Usan field, offshore Nigeria, between 740 and 760 m depth. This deep-water area is increasingly exploited for hydrocarbons, yet lacking in baseline biological information. Replicated remotely operated vehicle video transect surveys were carried out using industry infrastructure (through the SERPENT Project) at a representative range of slopes (1°, 3°, 11° and 29°). Twenty-four species of benthic megafaunal invertebrate were found, numerically dominated by the echinoid Phormosoma placenta, and nine species of fish were observed. Megafaunal invertebrate deposit feeder density decreased significantly with increasing slope (density range 0.503–0.081 individuals m−2). Densities of megafaunal suspension feeders were very low except at the highest slope site (mean density 0.17 m−2). Overall species richness was greater on steeper slopes, although the richness of deposit feeders was not affected. Reduced labile organic matter in sediments on steeper slopes likely reduced deposit feeder densities, but increased current flow at higher slopes allowed both increased richness and density of suspension feeders
Lebensspuren of the Bathyal Mid-Atlantic Ridge
Get PDFThe extent of megafaunal bioturbation was characterised at flat sedimented sites on the Mid-Atlantic Ridge (MAR) at 2500 m depth. This study investigated the properties of and spatial variation in surficial bioturbation at the MAR. Lebensspuren assemblages were assessed at four superstations either side of the MAR and in two different surface productivity regimes, north and south of the sub-polar front. High-definition ROV videos from these superstations were used to quantify area and abundance of 58 lebensspuren types. Lebensspuren area was lowest at the SW with 4.12% lebensspuren coverage and the SE & NW had the greatest area coverage of lebensspuren (9.69% for both). All stations except the SW were dominated by epifaunal, particularly track-style, lebensspuren. Infaunal mounds were more significant in the southern superstations, particularly in the SW. In terms of lebensspuren assemblage composition, all superstations were significantly different from one another, which directly corresponded with the composition of lebensspuren-forming epifauna. Lebensspuren assemblages appeared to have been primarily influenced by local-scale environmental variation and were independent of detrital flux. This investigation presented a novel relationship between lebensspuren and faunal density that conflicted with the traditionally held view of inverse proportionality and suggests that, at the MAR, megafaunal reworking was not the only significant control on lebensspuren assemblages
Geomorphological evidence of large vertebrates interacting with the seafloor at abyssal depths in a region designated for deep-sea mining
Get PDFExploration licences for seafloor mineral deposits have been granted across large areas of the world's oceans, with the abyssal Pacific Ocean being the primary target for polymetallic nodules—a potentially valuable source of minerals. These nodule-bearing areas support a large diversity of deep-sea life and although studies have begun to characterize the benthic fauna within the region, the ecological interactions between large bathypelagic vertebrates of the open ocean and the abyssal seafloor remain largely unknown. Here we report seafloor geomorphological alterations observed by an autonomous underwater vehicle that suggest large vertebrates could have interacted with the seafloor to a maximum depth of 4258 m in the recent geological past. Patterns of disturbance on the seafloor are broadly comparable to those recorded in other regions of the world's oceans attributed to beaked whales. These observations have important implications for baseline ecological assessments and the environmental management of potential future mining activities within this region of the Pacific
Deep-sea benthic megafaunal habitat suitability modelling: A global-scale maximum entropy model for xenophyophores
Get PDFXenophyophores are a group of exclusively deep-sea agglutinating rhizarian protozoans, at least some of which are foraminifera. They are an important constituent of the deep-sea megafauna that are sometimes found in sufficient abundance to act as a significant source of habitat structure for meiofaunal and macrofaunal organisms. This study utilised maximum entropy modelling (Maxent) and a high-resolution environmental database to explore the environmental factors controlling the presence of Xenophyophorea and two frequently sampled xenophyophore species that are taxonomically stable: Syringammina fragilissima and Stannophyllum zonarium. These factors were also used to predict the global distribution of each taxon. Areas of high habitat suitability for xenophyophores were highlighted throughout the world's oceans, including in a large number of areas yet to be suitably sampled, but the Northeast and Southeast Atlantic Ocean, Gulf of Mexico and Caribbean Sea, the Red Sea and deep-water regions of the Malay Archipelago represented particular hotspots. The two species investigated showed more specific habitat requirements when compared to the model encompassing all xenophyophore records, perhaps in part due to the smaller number and relatively more clustered nature of the presence records available for modelling at present. The environmental variables depth, oxygen parameters, nitrate concentration, carbon-chemistry parameters and temperature were of greatest importance in determining xenophyophore distributions, but, somewhat surprisingly, hydrodynamic parameters were consistently shown to have low importance, possibly due to the paucity of well-resolved global hydrodynamic datasets. The results of this study (and others of a similar type) have the potential to guide further sample collection, environmental policy, and spatial planning of marine protected areas and industrial activities that impact the seafloor, particularly those that overlap with aggregations of these conspicuously large single-celled eukaryotes
Techniques for monitoring the recovery of deep, cold-qater habitats following physical disturbance from drilling discharges
No full textRecovery of deep, cold-water benthic habitats following physical disturbance caused by discharges of cuttings and water-based mud (WBM) from drilling have been measured using Remotely Operated Vehicle (ROV) sampling techniques. Video data were collected from a well site in the Laggan field in the Faroe-Shetland channel immediately after discharge and again two years after discharge. Data were also collected on baseline conditions and from a nearby well site to provide data on recovery ten years after discharge. Faunal abundance and diversity parameters were quantified from the video and used to assess the community-level disturbance and recovery. Initial disturbance resulted in a reduction in faunal diversity and density from baseline levels close to drilling activity (<100 m). After two years and within 100 m of the drilling activity assemblages were still significantly different in composition and lower in diversity and density. Recovery was observed after ten years as increases in faunal density and diversity close to the site of previous drilling activity. In the area completely covered by cuttings (approx. 30 m radius), there were few megafauna observed in any survey. This work was carried out opportunistically as part of an environmental impact assessment and in stand-by time from a drilling rig. The use of existing technology in stand-by time provides oil and gas operators with opportunities to integrate routine environmental monitoring into normal operations providing a cost-effective and scientifically robust monitoring method
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