TOBI sidescan sonar mapping of carbonate mound provinces and channel heads in the Porcupine Seabight, W. of Ireland

A large-scale sidescan sonar survey, using the 30 kHz TOBI system of the SOC, was carried out in summer 2002 over the carbonate mound provinces of the Porcupine Seabight and Rockall Trough, W of Ireland (EASSS III contract HPRI-CT-1999-00047, survey partly on behalf of the Porcupine Studies Group). The survey in the Porcupine Seabight focused on the Hovland-Magellan province in the north and the Belgica province on the eastern flank of the basin. Furthermore a reconnaissance track was added over the canyon heads of the Gollum Channel System further south in the Seabight.Each area has different characteristics. The Hovland-Magellan province shows a very homogeneous backscatter in the sidescan mosaics, indicating a quiet depositional environment. Mounds appear as sharp features with a strong backscatter and an acoustic shadow. Some Hovland mounds form multiple, ridge-like structures of more than a km in length. The Magellan mounds are nearly all buried, but leave subtle topographic effects at the seafloor.The Belgica mound province is characterised by much less homogeneous backscatter and a steeper seafloor slope. The mounds are placed en echelon along the slope and are bound to the W by a blind channel. Smaller down-slope channels are also found between the mounds. Many small, high-backscatter features, interpreted as incipient (’Moira’) mounds have been found in this province. Striations in the blind channel, and higher up on the slope of the Belgica province indicate the influence of high current speeds. Pockmarks have been found just south of the Belgica province. The Gollum Channels are steep-flanked, U- or V-shaped channels of ca. 200 m deep. Their steep walls are cut by gullies and feeder channels, and evidence of slope failures is present. Lineations and high-backscatter patches are found on some of the channel floors

Structure and development of carbonate mounds along the NE Atlantic margin

Giant carbonate mounds between 500-1200 m water depth along both the SE and SW margins of Rockall Trough rise 5 to 300 m above the surrounding seafloor and have diameters at their basis of up to 5 km. Buried mounds, at relatively shallow depth below the seafloor are also found. Both individual and complex clusters of mounds can be recognized. Smaller and individual, sometimes buried mounds are found at the upper slope. On the SW Rockall Trough margin, higher, steeper and individual mounds are found deeper downslope (900-1100 m). At the middle slope the mounds merge into a complex structure and form complex clusters with a very irregular upper surface and an apparent lack of internal reflectors (600-1000 m depth). These clusters are oriented perpendicular and slightly oblique to the prevailing bathymetry, and show on TOBI profiles as linear ridges. Further results of the TOBI survey in summer 2002 show that the distribution of mounds along the flanks of SW Rockall Trough is considerably more widespread than previously considered, and also that the mounds appear to form constructional elements on a large plateau. Erosional channels between mounds identify the strong interaction between mound shape and strong bottom currents along the slopes of mounds. On the upper flank the mounds are delineated by a field of large gravelly sediment waves of 500m wavelength oriented parallel to the margin in the central part and more curved to the north. On their lower flank slide scars do locally occur

Deep-water oyster cliffs at La Chapelle Bank (Celtic Margin)

The maiden voyage of Ghent University’s ROV GENESIS on-board R/V Belgica (13-20 June 2006) has succeeded in contributing to several objectives of the EU-projects HERMES and EURODOM, as well as of the ESF Euromargins project MoundForce. After several trials in the Bay of Douarnenez, GENESIS made its first deep-water survey dives off the Banc de la Chapelle, on the Celtic margin, down to 700 m. The French canyon system near the Banc de la Chapelle offered a perfect location for rigorous trials of GENESIS: reported cold-water coral finds, rugged topography and hydrodynamics in a setting linking the shelf seas to the deep marine realm. The area was first surveyed using R/V Belgica’s multibeam echosounder, imaging deep canyons and thalweg channels between prominent spurs where corals had been reported. High resolution seismic sparker lines provided a geological context and linked in to the existing seismostratigraphy.Two successful dives revealed a sandy-muddy seabed with curious bedforms and erosion exposing consolidated sedimentary sequences, often cut by vertical cliffs up to 10m high. At the base of the cliffs, fallen blocks provided settlement sites for sessile organisms whilst the cliffs and protruding banks revealed dense communities of unidentified giant ostreidae (probably Neopycnodonte sp) forming 3D assemblage with occasional cold-water coral colonies (Lophelia pertusa). Though deep-water ‘oyster banks’ of Neopyncodonte cochlear had already been reported in the Bay of Biscay by ..Le Danois (1948) based on dredges, these dramatic seascapes had remained largely hidden to the human eye up to now

On the Timing and Nature of the Multiple Phases of Slope Instability on Eastern Rockall Bank, Northeast Atlantic

One of the most challenging tasks when studying large submarine landslides is determining whether the landslide was initiated as a single large event, a chain of events closely spaced in time or multiple events separated by long periods of time as all have implications in risk assessments. In this study we combine new multichannel seismic profiles and new sediment cores with bathymetric data to test whether the Rockall Bank Slide Complex, offshore western Ireland, is the composite of multiple slope collapse events and, if so, to differentiate them. We conclude that there have been at least three voluminous episodes of slope collapse separated by long periods of slope stability, a fourth, less voluminous event, and possibly a fifth more localized event. The oldest event, Slide A (200 km3), is estimated to be several hundred thousand years old. The second event, Slide B (125 km3), took place at the same location as slide A, reactivating the same scar, nearly 200 ka ago, possibly through retrogression of the scarp. Slide C (400 km3) took place 22 ka ago and occurred further north from the other slides. Slide D was a much smaller event that happened 10 ka ago, while the most recent event, albeit very small scale, took place within the last 1,000 years. This study highlights the need to thoroughly investigate large slide complexes to evaluate event sequencing, as seismic studies may hide multiple small‐scale events. This work also reveals that the same slide scarps can be reactivated and generate slides with different flow behaviors

Geomorphological drivers of deeper reef habitats around Seychelles

Mesophotic (30–150 m) and rariphotic (150–300 m) deeper reef habitats are important from an ecological and conservation perspective, yet remain understudied. Key knowledge gaps exist on the environmental patterns and processes that drive and shape their geographical distributions. Understanding these is particularly important for regions as the Western Indian Ocean, where deeper reefs are poorly known but support food security and host economically important species. Spatial predictive models of assemblage occurrences, using terrain variables as predictors, offer a solution to address knowledge gaps around deeper reef distributions. We identified relationships between seafloor geomorphology, quantified at multiple scales, and sessile benthic assemblages in four atoll seascapes in Seychelles using terrain models derived from high-resolution multibeam sonar and underwater video surveys. Using random forests and boosted regression trees, we demonstrated that terrain derivatives extracted over multiple scales perform as reliable predictors of deeper reef assemblages. The most influential environmental predictors were depth, distance to shore, topographic complexity, slope and curvature and substrate characteristics. The relative importance of predictors was explained by assemblage functional characteristics. Assemblage–environment relationships were used to produce probability distribution maps that showed similar distributional patterns for identified assemblages across locations, with high occurrence probabilities linked to complex geomorphological structures. Our results help contribute to a consistent baseline understanding of the relationship between seascape structure and mesophotic reef ecosystems in this area. Complex geomorphological structures, including terraces and paleoshorelines, supported high densities of mesophotic assemblages and could be considered priority habitats for management

Mapping, quantifying and comparing seascape heterogeneity of Southwest Indian Ridge seamounts

Context Seamounts are abundant geomorphological features creating seabed spatial heterogeneity, a main driver of deep-sea biodiversity. Despite its ecological importance, substantial knowledge gaps exist on the character of seamount spatial heterogeneity. Objectives This study aimed to map, quantify and compare seamount seascapes to test whether individual habitats and seamounts differ in geomorphological structuring, and to identify spatial pattern metrics useful to discriminate between habitats and seamounts. Methods We mapped and classified geomorphological habitat using bathymetric data collected at five Southwest Indian Ridge seamounts. Spatial pattern metrics from landscape ecology are applied to quantify and compare seascape heterogeneity in composition and configuration represented in resulting habitat maps. Results Whilst part of the same regional geological feature, seamounts differed in seascape composition and configuration. Five geomorphological habitat types occurred across sites, which within seamounts differed in patch area, shape and clustering, with ridge habitat most dissimilar. Across seamounts, the spatial distribution of patches differed in number, shape, habitat aggregation and intermixing, and outcomes were used to score seamounts on a gradient from low to high spatial heterogeneity. Conclusions Although seamounts have been conceptualised as similar habitats, this study revealed quantitative differences in seascape spatial heterogeneity. As variations in relative proportion and spatial relationships of habitats within seamounts may influence ecological functioning, the proposed quantitative approach can generate insights into within-seamount characteristics and seamount types relevant for habitat mappers and marine managers focusing on representational ecosystem-based management of seamounts. Further research into associations of sessile and mobile seamount biodiversity with seascape composition and configuration at relevant spatial scales will help improve ecological interpretation of metrics, as will incorporating oceanographic parameters

RNA interference in Lepidoptera: an overview of successful and unsuccessful studies and implications for experimental design

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Search for Limiting Factors in the RNAi Pathway in Silkmoth Tissues and the Bm5 Cell Line: The RNA-Binding Proteins R2D2 and Translin

RNA interference (RNAi), an RNA-dependent gene silencing process that is initiated by double-stranded RNA (dsRNA) molecules, has been applied with variable success in lepidopteran insects, in contrast to the high efficiency achieved in the coleopteran Tribolium castaneum. To gain insight into the factors that determine the efficiency of RNAi, a survey was carried out to check the expression of factors that constitute the machinery of the small interfering RNA (siRNA) and microRNA (miRNA) pathways in different tissues and stages of the silkmoth, Bombyx mori. It was found that the dsRNA-binding protein R2D2, an essential component in the siRNA pathway in Drosophila, was expressed at minimal levels in silkmoth tissues. The silkmoth-derived Bm5 cell line was also deficient in expression of mRNA encoding full-length BmTranslin, an RNA-binding factor that has been shown to stimulate the efficiency of RNAi. However, despite the lack of expression of the RNA-binding proteins, silencing of a luciferase reporter gene was observed by co-transfection of luc dsRNA using a lipophilic reagent. In contrast, gene silencing was not detected when the cells were soaked in culture medium supplemented with dsRNA. The introduction of an expression construct for Tribolium R2D2 (TcR2D2) did not influence the potency of luc dsRNA to silence the luciferase reporter. Immunostaining experiments further showed that both TcR2D2 and BmTranslin accumulated at defined locations within the cytoplasm of transfected cells. Our results offer a first evaluation of the expression of the RNAi machinery in silkmoth tissues and Bm5 cells and provide evidence for a functional RNAi response to intracellular dsRNA in the absence of R2D2 and Translin. The failure of TcR2D2 to stimulate the intracellular RNAi pathway in Bombyx cells is discussed