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Since 1998, Woodside Mauritania Pty Ltd has been exploring for hydrocarbon deposits offshore from the Islamic Republic of Mauritania, in Northwest Africa. A 3-D seismic survey, undertaken in 1999–2000, revealed the presence of buried and seabed carbonate mounds at approximately 450–550 m water depth on the continental slope. These mounds are approximately 100 m in height, 500 m wide at the base, and cover a linear extent of at least 190 km. Core samples from the mounds were found to contain dead fragments of four species of cold-water corals: Lophelia pertusa, Madrepora oculata, Solenosmilia variabilis and Desmophyllum sp. In 2002, a preliminary towed camera survey revealed large areas of coral rubble at two mound sites suggesting that corals were previously a dominant component of the benthic community. A second video survey, in 2003, recorded some live hard coral polyps and a single live coral colony, probably L. pertusa , at one of the mound sites. Coral rubble at all sites surveyed was found to support epibenthic invertebrate and fish assemblages. The mound areas surveyed may have been exposed to physical impacts that have resulted in damage of coral colonies previously inhabiting these features. Based on the nature of the damage and past and present demersal fishing activity in the region, bottom trawling could have caused these impacts. The discovery of a significant deep-water reefal system offshore Mauritania has implications for future management of trawling and oil exploration activities. These issues are discussed in the context of the potential biodiversity significance and conservation importance of the carbonate mud mounds and their associated biological communities.

Deep-water Oculina coral reefs, which are similar in structure and development to deep-water Lophelia reefs, stretch 167 km (90 nm) at depths of 60–100 m along the eastern Florida shelf of the United States. These consist of numerous pinnacles and ridges, 3–35 m in height, that are capped with thickets of living and dead coral, Oculina varicosa . Extensive areas of dead Oculina rubble are due in part to human impacts (e.g., fish and shrimp trawling, scallop dredging, anchoring, bottom longlines, and depth charges) but also may be due in part to natural processes such as bioerosion, disease, or global warming. In the 1970s, the reefs were teeming with fish. By the early 1990s, both commercial and recreational fisheries had taken a toll on the reefs, especially on the coral habitat and populations of grouper and snapper. In 1984, 315 km^2 (92 nm^2) was designated the Oculina Habitat of Particular Concern (OHAPC), prohibiting trawling, dredging, bottom longlines and anchoring, and establishing the first deep-sea coral marine protected area in the world. In 2000, the Oculina Marine Protected Area (MPA) was expanded to 1029 km^2 (300 nm^2). Despite these protective measures, manned submersible and ROV observations in the Oculina MPA between 1995 and 2003 suggest that portions of the coral habitat have been reduced to rubble since the 1970s, grouper spawning aggregations may be absent, and illegal trawling continues. This paper is a review of the results of the mapping, habitat characterization, and fish surveys from the early historical studies (1960–1980s) to the more recent surveys (1995–2003).

Documentation of hundreds of locations for Canadian deep-water corals has been obtained through scientific initiatives and local fishermen’s knowledge. Using these locations, as well as relevant oceanographic data, this study determined areas of suitable habitat for Paragorgia arborea and Primnoa resedaeformis along the Canadian Atlantic continental shelf and shelf break using predictive models. The study area included a band approximately 800 km long x 200 km wide from Cape Breton to the Gulf of Maine, and was chosen based on density of coral sites. Several environmental factors including slope, temperature, chlorophyll a , current speed and substrate may be important in determining suitable coral habitat and were included in the analysis. There are many different techniques used to model habitats, but frequently they are limited by the type of data available. Comparatively, few techniques using presence-only data are available. We utilized BioMapper, a program which uses Ecological Niche Factor Analysis (ENFA), to generate habitat suitability maps by relating data on species presence with background environmental data to determine the species’ niche. We found that habitat requirements differed between the two species of coral. For Paragorgia arborea , the niche was highly specialized, and characterized by steeply sloped environments and rocky substrate. In contrast, for Primnoa resedaeformis , suitable habitat was more broadly distributed in the study area, and located in areas with high current speed, rocky substrates and an approximate temperature range between 5 and 10°C. This is the first study to use predictive modelling to identify suitable habitat for deep-water coral, which may prove an important tool for the conservation of these organisms.

The environmental sensitivies of cold-water corals and their associated biota are likely to be determined by the natural variability of the cold-water coral reef environment. The sensitivity of reef biota to sedimentation and resuspension events is largely unknown and the influence of seasonal phytodetrital deposition is poorly understood. Here we describe the use of a benthic photolander to monitor this variability by the Sula Ridge reef complex on the mid-Norwegian continental shelf and from the Galway carbonate mound in the Porcupine Seabight. The photolander provides a platform for time-lapse digital and film cameras to image the seabed while recording the current regime and optical characteristics (light transmission, backscatter and fluorescence) of the seawater. In its first two deployments carried out in 2001 and 2002 by the Sula Ridge the lander recorded a dynamic environment around the reef site with a tidal current regime and periods of sediment resuspension. Current speeds by the Sula Ridge reef complex reached a maximum of 28 cm s^−1 and 70 cm s^−1 on the Galway carbonate mound, reinforcing much speculation about the dependence of these communities on current-swept conditions. Seabed photographs show intense feeding activity of echiuran worms ( Bonellia viridis ) near the Sula Ridge reef complex pointing to rapid bioturbation of the sediment. Fish were recorded sheltering near sponges that had colonised glacial dropstones. Longer term monitoring in situ is needed for study of seasonal change, to identify functional roles of associated fauna and to monitor potential coral spawning events. Benthic landers and seafloor observatories have great potential in these areas. Only with a better understanding of the natural variability of the cold-water coral environment can informed decisions about the environmental sensitivity of cold-water coral reefs and their management be made.

The dynamics that occur at the Porcupine Bank, Rockall Trough, are described in relation to the role the bank, and others like it, may play in the development of deep-water corals, such as Lophelia pertusa (L.), which occurs widely in the NE Atlantic. High productivity has been measured over the bank, and it appears that this productivity may be fuelled by an increase in nutrients available over the bank through winter convection which leaves dense, nutrient rich water on the bank. This dense water drains away slowly through the benthic boundary layer (BBL) providing a mechanism for downslope transport of organic material in the boundary layer. Processes such as rectification of diurnal tides and Taylor column formation generate closed circulation patterns around the bank and promote the retention of organic matter over the bank. Similar processes have been observed over other Rockall Trough banks, and the combination of these processes appear to promote the availability of food to the corals that inhabit the lower flanks of the banks, particularly on the coral-dominated carbonate mounds that also occur there.

This paper presents an overview of the spatial distribution and morphology of coral banks in the Porcupine Seabight in relation to their environmental settings. The study area is characterised by well-delimited clusters of coral banks, each featuring typical bank morphology and environmental setting. In the central part of the basin, two mound provinces can be identified: a set of complex fl at topped seafloor mounds in the Hovland Mound province is flanked to the north by a crescent of numerous north-south elongated buried coral banks in the Magellan Mound province, along the eastern margin of the basin partly buried and seabed coral banks represent the Belgica Mound province. The banks are mound-shaped elevations, many of them hosting living deep-water corals ( Lophelia pertusa, Madrepora oculata, Desmophyllum cristagalli, Dendrophyllia sp.) and associated fauna. This active biological layer covers a dead assemblage of corals clogged with mud. All coral banks, buried or seabed, occur in association with current-induced features (e.g., scouring features, dunes) and steep palaeo- and present-seabed slopes. Only a few banks have a present-day seabed expression, which suggests that environmental conditions have been more favourable for bank development in the past. The depth range of the seabed coral banks coincides with the Mediterranean Outflow Water which may control indirectly the coral distribution. The distribution of corals in the southern part of the North Atlantic and the actual link with Mediterranean water suggest a possible migration of corals within the Mediterranean water along the NE Atlantic margin. The start-up phase of the coral bank development in the basin has taken place simultaneously for all provinces, and tentatively framed in times subsequent to a Late Pliocene period of erosion and non-deposition. It is considered that the sedimentary load of the currents plays an important role in the bank development. Coral banks accrete by the active baffling of sediment by the biological framework and growth of the biological cap. When sedimentation and biological growth get out of balance, the framework will progressively be clogged with sediment. Once sediment dominates the structure the coral banks get buried and draped by sediment.

Carbonate mounds, identified as deep-water coral banks, have been reported recently from three provinces in the Porcupine Seabight, SW of Ireland. As yet, the mechanisms behind their formation and development are only partly understood. This contribution discusses their seabed appearance and present-day sedimentary environment, based on a large-scale TOBI sidescan sonar mapping carried out in 2002, and on detailed ROV video records from specific sites within the three mound provinces, collected in 2001. The study of the present-day characteristics and variability of these mounds can help to understand their development history in the past. The imagery clearly shows that the sedimentary environment in the Magellan and Hovland Mound provinces in the northern Porcupine Seabight is much quieter than in the current-swept Belgica Mound province on the eastern flank of the basin. In the latter area, for example, gravel lags and coarse sediments are found, together with patches of sorted sands, striations, barchan dunes and sediment waves. The difference in environment results in different mound appearances. The richest coral communities with the most abundant live coral occurrences are found in the Belgica province, while for example on the Magellan Mounds only a few live coral colonies are left. The present-day situation of the coral banks in the Porcupine Seabight thus illustrates the influence of the interplay between current and sediment dynamics on coral growth and mound development.

Carbonate mounds (up to 200 m high) formed from the accumulated remains of cold-water corals (principally Lophelia pertusa and Madrepora oculata ), associated calcareous fauna and interstitial sediment are present at 500–1000 m water depths west of Ireland. Seabed mapping datasets (side-scan sonar, multibeam echosounder, sub-bottom profiler and underwater video imagery) are presented here from the Belgica Mound province on the eastern Porcupine Seabight margin. The data, integrated within a Geographic Information System (GIS), provide an environmental context to mound development. Analysis of this multidisciplinary dataset and resultant facies map highlight differing sedimentary processes (e.g., sediment wave, barchan dune, gravel lag and sand ribbon development) operating under strong northward flowing bottom currents with sandy sediment supply where the influence of mound topography on benthic currents and sediment pathways is evident. Correspondingly, benthic current pathways and associated sediment transport also exert an influence on carbonate mound surface morphology and growth. Giant mounds show a transition from sediment waves that, with increasing coral colonisation, give way to banks of coral towards the mound summits. Smaller mound features (Moira Mounds) show sand entrapment as an important mound-forming process.

Sponge reefs in the Queen Charlotte Basin exist at 165–240 m depth within tidally influenced shelf troughs subject to near bottom current velocities of 25–50 cm s^−1 where nutrient supply from coastal runoff is augmented by wind-induced upwelling of nutrient rich water from the adjacent continental slope. Large reef mounds to 21 m in elevation affect tidally driven bottom currents by deflecting water flows through extensive reef complexes that are up to 300 km^2 in area. Three hexactinellid species construct reefs by building a siliceous skeletal framework through several frame-building processes. These sponge reefs exist in waters with 90 to 150 µM dissolved oxygen, a temperature range of 5.9 to 7.3°C and salinity of 33.2 to 33.9 ‰. Relatively high nutrient levels occur at the reef sites, including silica, which in bottom waters are typically >40 µM and may be up to 80 µM. A high dissolved silica level is potentially an important control on occurrence of these and other dense siliceous sponge populations. The sponge reefs are mainly confined to seafloor areas where exposed iceberg plough marks are common. Sediment accumulation rates are negligible on the relict, glacial surface where the reefs grow, and trapping of flocculated suspended particulate matter by hexactinosidan or framework skeleton hexactinellid sponges accounts for a large proportion of the reef matrix. Suspended sediment concentration is reduced within the nepheloid layer over reef sites suggesting efficient particle trapping by the sponges. The reef matrix sediments are enriched in organic carbon, nitrogen and carbonate, relative to surrounding and underlying sediments. The sponges baffle and trap suspended sediments from water masses, which in one trough have a residence time of approximately 6 days, ensuring a close association of the sponges with the bottom waters. The location of the reef complexes at the heads of canyons provide a means of regionally funnelling particulate material that sponges can trap to enrich their environment with organic carbon and biogenic silica. Like deepsea coral reefs, the sponge reefs are a remote and poorly known ecosystem that can present logistical challenges and survey costs. Also like deep-sea coral reefs, many of the hexactinosidan sponge reefs have been damaged or destroyed by the groundfish trawl fishery.

Topographic and geophysical seafloor mapping has shown that in some areas there apparently is a close relationship between pockmarks and coral reefs. Off Norway there are three such occurrences: The Haltenpipe Reef Cluster (HRC), the Fugløy Reefs, and reefs in the Kristin hydrocarbon field. In the Porcupine area off Ireland, there is also a close relationship between large pockmark-like depressions and carbonate mounds with corals. Such is also the case with the Darwin Mounds, at 1000 m depth, where pockmarks occur close to the mounds containing Lophelia corals. In the Gulf of Mexico and off Brazil there are similar associations. At the Kristin hydrocarbon field off Mid-Norway (located 130 km NW of the HRC and the Sula Ridge Reefs), pockmarks and coral reefs occur in abundance. Out of 120 reefs mapped within an area of 14 km^2, there are 33 reefs that occur inside or along the inside rim of pockmarks. Most of the other 87 reefs are located within 200 m of a pockmark. The largest reefs at Kristin are up to 3.5 m high and 90 m in length. The observed co-occurrence between corals and pockmarks suggests that gas and porewater emanating from pockmarks stimulates coral growth, probably through the provision into the water column of a stable food (nutrient) supply, in the form of bacteria and micro-organisms. This theory has previously been called the “hydraulic theory” for coral reefs. Both of the new (Kristin and Fugløy) reef/pockmark cases strengthen the validity of this theory. Furthermore, this close association also indicates that the sessile animals living in these reefs ( Lophelia, Paragorgia, Primnoa, Acesta , etc.) may be more robust and tolerant to episodes of silting than previously suspected.