1,721,000 research outputs found
Deep-water observation of scalloped hammerhead Sphyrna lewini in the western Indian Ocean off Tanzania
Get PDFA scalloped hammerhead Sphyrna lewini was observed opportunistically from a remotely operated vehicle 1 m off the seabed at 1042 m depth, during hydrocarbon exploration activities in the Ruvuma Basin off Tanzania. The observation, which occurred during night hours, is the deepest accurately recorded for this species and the first deep-water record for the Indian Ocean. The record adds support for the occurrence in deep water during night hours being a widespread and possibly common behaviour in this species, and further expands a small but growing literature that meso- and bathypelagic environments may be of greater importance to elasmobranchs previously considered to be primarily epipelagic
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
Recovery of benthic megafauna from anthropogenic disturbance at a hydrocarbon drilling well (380m depth in the Norwegian Sea)
No full textRecovery from disturbance in deep water is poorly understood, but as anthropogenic impacts increase in deeper water it is important to quantify the process. Exploratory hydrocarbon drilling causes physical disturbance, smothering the seabed near the well. Video transects obtained by remotely operated vehicles were used to assess the change in invertebrate megafaunal density and diversity caused by drilling a well at 380 m depth in the Norwegian Sea in 2006. Transects were carried out one day before drilling commenced and 27 days, 76 days, and three years later. A background survey, further from the well, was also carried out in 2009. Porifera (45% of observations) and Cnidaria (40%) dominated the megafauna. Porifera accounted for 94% of hard-substratum organisms and cnidarians (Pennatulacea) dominated on the soft sediment (78%). Twenty seven and 76 days after drilling commenced, drill cuttings were visible, extending over 100 m from the well. In this area there were low invertebrate megafaunal densities (0.08 and 0.10 individuals m?2) in comparison to pre-drill conditions (0.21 individuals m?2). Three years later the visible extent of the cuttings had reduced, reaching 60 m from the well. Within this area the megafaunal density (0.05 individuals m?2) was lower than pre-drill and reference transects (0.23 individuals m?2). There was a significant increase in total megafaunal invertebrate densities with both distance from drilling and time since drilling although no significant interaction. Beyond the visible disturbance there were similar megafaunal densities (0.14 individuals m?2) to pre-drilling and background surveys. Species richness, Shannon-Weiner diversity and multivariate techniques showed similar patterns to density. At this site the effects of exploratory drilling on megafaunal invertebrate density and diversity seem confined to the extent of the visible cuttings pile. However, elevated Barium concentration and reduced sediment grain size suggest persistence of disturbance for three years, with unclear consequences for other components of the benthic fauna
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
Observations of sedimentation near a hydrocarbon drilling site and impacts on a sponge specimen
No full textThe data consist of hourly observations of sedimentation impacts located approximately 31 m southwest of the drilling location, including measurements of proxies of suspended material in the water column, along with observations of the lamellate desmosponge specimen. Acoustic backscatter (1.9-2.0 MHz) and current speed were measured using a Seaguard RCM DW. A time-lapse camera was also deployed: the Nikon E995 camera was set to F 6.0, ISO 200, exposure 1/60, with photos of 2048 x 1536 pixels. As another estimate of suspended material in the water column, brightness (as mean RGB) was calculated for top corners (256 x 256 pixels) in photos, where the corners were not obscured by fish. Settlement of sediment on the sponge specimen was estimated as brightness of a portion of it (approximately 3600 pixels2) in the images. Movement of the sponge was estimated as the distance between successive xy-positions of the apex of the sponge in images. Mean values (6- and 12-hourly) centred on the hourly data, and sums of distance over 6- and 12-h periods were also calculated
Figure 5 in Behaviour and habitat of Neohela monstrosa (Boeck, 1861) (Amphipoda: Corophiida) in Norwegian Sea deep water
No full textFigure 5. Typical distribution of Neohela monstrosa burrows in a densely populated area. The photo from a video transect at station 301 at 1935 m depth shows ~15 burrows made by small (white arrows) and large (black arrows) individuals. Scale is indicated by two laser spots that are 10 cm apart.Published as part of Buhl-Mortensen, Lene, Tandberg, Anne Helene S., Buhl-Mortensen, Pål & Gates, Andrew R., 2015, Behaviour and habitat of Neohela monstrosa (Boeck, 1861) (Amphipoda: Corophiida) in Norwegian Sea deep water, pp. 323-337 in Journal of Natural History 50 on page 331, DOI: 10.1080/00222933.2015.1062152, http://zenodo.org/record/398335
Infection with cerebral metacercariae of microphallid trematode parasites reduces reproductive output in the gammarid amphipod Gammarus insensibilis (Stock 1966) in UK saline lagoons
No full textAbstractSaline lagoons are priority habitats in the United Kingdom supporting several protected specialist species. One specialist, the amphipod Gammarus insensibilis, is infected with behaviour-altering microphallid trematodes such as Microphallus papillorobustus. In saline lagoons around the coast of England (Gilkicker and Lymington–Keyhaven on the Hampshire coast and Moulton Marsh in Lincolnshire) there is variation in the prevalence of this parasite in the gammarid populations (0 at Salterns in the Lymington–Keyhaven lagoon system to 98% at Gilkicker). Infection intensity ranged from 0 to 20 metacercariae in individual amphipods. Higher infection intensity can alter the shape of the amphipod's head. Under experimental conditions respiration rate is significantly reduced in infected animals and reproductive output (expressed as early stage embryos mg g dry weight−1) is significantly lower in infected females. It is important to consider the role of host–parasite interactions in order to understand the ecology of specialist lagoon species such as G. insensibilis and their lagoon habitats.<br/
Autonomous marine environmental monitoring: Application in decommissioned oil fields
Get PDFHundreds of Oil & Gas Industry structures in the marine environment are approaching decommissioning. In most areas decommissioning operations will need to be supported by environmental assessment and monitoring, potentially over the life of any structures left in place. This requirement will have a considerable cost for industry and the public. Here we review approaches for the assessment of the primary operating environments associated with decommissioning — namely structures, pipelines, cuttings piles, the general seabed environment and the water column — and show that already available marine autonomous systems (MAS) offer a wide range of solutions for this major monitoring challenge. Data of direct relevance to decommissioning can be collected using acoustic, visual, and oceanographic sensors deployed on MAS. We suggest that there is considerable potential for both cost savings and a substantial improvement in the temporal and spatial resolution of environmental monitoring. We summarise the trade-offs between MAS and current conventional approaches to marine environmental monitoring. MAS have the potential to successfully carry out much of the monitoring associated with decommissioning and to offer viable alternatives where a direct match for the conventional approach is not possible
An association between a cusk eel (Bassozetus sp.) and a black coral (Schizopathes sp.) in the deep western Indian Ocean
Get PDFDetailed observations in the deep sea can reveal previously unknown behaviour, species interactions and fine-scale habitat heterogeneity. Here, the first in situ images of the black coral Schizopathes sp. (Anthozoa: Antipatharia) in the deep western Indian Ocean have been obtained from remotely operated vehicle video footage and time-lapse photography. In these images, there appears to be an association with the cusk eel Bassozetus (Family: Ophidiidae). In the primary observation, chance encounters revealed the fish interacted with the anitpatharian on multiple occasions over several days. Subsequent time-lapse camera footage showed the fish remained almost exclusively underneath the antipatharian for the duration of a 30-h deployment. Excursions from the cover of the antipatharian were for less than 2 min. The primary observation is supported by two similar encounters in the same region. Observed reduction in the tail-beat frequency of the fish under the antipatharian suggests reduced energy requirements for the ophidiid in this position. The observations demonstrate the role that even individual coral colonies play as a source of three-dimensional structure, providing habitat heterogeneity in the deep sea
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