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The Giant Cold-Water Coral Mounds Barrier Off Mauritania
Abstract
This chapter describes the main features of the giant mounds structure running parallel to the shelf break along the Mauritanian slope between the Senegalese border and Cape Timiris. At over 580 km long, it is the world’s largest identified cold-water coral mounds barrier and, in our opinion, conforms to a single province, the Mauritanian Province. The Maurit series of Spanish-Mauritanian oceanographic surveys collected multibeam echosounder data, performed 16 conductivity-temperature-depth (CTD) profiles and 13 rock dredgesamplings, which led to the mapping of the reefcomplex, oceanographic characterization of water masses and faunistic studies. The reef framework is mostly composed of dead coral, mainly Lophelia pertusa, with a minor fraction of Madrepora oculata. Associated fauna mainly consists of Acesta excavata and other bivalve and prosobranch molluscs, soaked in abundant, fine compacted mud. At least 150 macrobenthic species of 27 high-range taxa inhabit this reef. The coral surface is either almost devoid of sessile fauna or poorly colonized by small encrusting epifaunal species. We only found fragments of living L. pertusa in the four southernmost stations. The multivariate analysis clearly groups some areas where corals and other suspension-feeders exhibit the highest diversity. Despite their small size, the 17 taxa of suspension-feeders represent 75% of abundance and biomass. Surprisingly, despite the unfavourable history of climatic change episodes, current environmental conditions, deterioration and overall faunistic poverty of the mounds, Lophelia specimens still survive in some areas, sheltering communities of apparently similar structure to those on well-developed cold-water coralreefs in Northern Atlantic latitudes.
... The impact of low DO on CWC growth was observed clearly for the first time in the hiatus in a Mediterranean coral mound record coinciding with sapropel S1 event (Fink et al., 2012). The giant coral mound province off Mauritania (Colman et al., 2005) has been discovered within oxygen-depleted intermediate waters in which DO range between 0-1.3 mL L -1 (Ramos et al., 2017). These low DO have been considered as the main stressor determining the scarce present-day occurrence of living CWC off Mauritania, but also one of the environmental factors responsible for the aggradational hiatuses in the regional coral mound records (Wienberg et al., 2018). ...
... However, the recent discovery of coral mound provinces (CMPs) under tropical upwelling zones and associated oxygen minimum zones revealed living (but sporadic) Lophelia colonies 1.1-1.4 mL L −1 off Mauritania (Ramos et al., 2017;Wienberg et al., 2018) and thriving reefs (with associated large M. oculata colonies) even under DO values < 1 mL L −1 (Hanz et al., 2019;Orejas et al., 2021). ...
... Turning the CWC colonies into coral mounds require that favourable conditions for CWC are maintained over millennial timescales, combined with sufficient sediment supply, as suggested by the compilation of Wienberg and Titschack (2017). The discoveries of new CMPs (e.g., CMPs under low dissolved oxygen concentrations ;Colman et al., 2005;Hanz et al., 2019;Hebbeln et al., 2020;Ramos et al., 2017;Wienberg et al., 2018), as well as by several biological studies based on aquaria experiments (Baussant et al., 2017;e.g., Brooke and Young, 2009;Büscher et al., 2017;Dorey et al., 2020;Hennige et al., 2014;Larsson et al., 2013;Lunden et al., 2014;Maier et al., 2009;Naumann et al., 2014;Orejas et al., 2016;Weinnig et al., 2020) constantly improve the definition of the boundary conditions for CWC. The wide range of boundary conditions detected so far likely suggests a potential capacity of CWC to cope with quite different environmental conditions (phenotypic plasticity) apparently without evident genetic variations (Flot et al., 2013). ...
Over the last 25 years, extensive geological investigations on coral mounds, seafloor structures in the deep-sea built by ecosystem-engineering cold-water corals (CWC), have revealed that the spatial and temporal occurrences of CWC depend on environmental and climate conditions. Coral mounds in the NE Atlantic were the first and have been the most studied coral mound provinces (CMPs), providing the fundamental evidence of the environmental forcing supporting CWC and on the development of coral mounds over glacial-interglacial cycles. However, the continuous discovery of coral mounds under the extremely variable oceanographic conditions along the Atlantic margins have brought new evidence to re-discuss our previous knowledge on CWC and coral mounds.
This study was designed for one of the latest CMP discovered: the Namibian coral mounds. More than 2000 mounds are sitting on the Namibian inner shelf (~20°S) between 160-270 m water depths. The Namibian CMP occurs under an oceanographic setting controlled by the Benguela Upwelling System (BUS). The BUS is one of the large eastern-boundary upwelling systems with the highest primary production in the world ocean. Due to these highly productive conditions, shelf-bottom waters become severely oxygen-depleted resulting from the consumption of oxygen through the decomposition of organic matter. The Namibian coral mounds occur exactly at the core of the local oxygen minimum zone (OMZ, 160–270 m water depth), where dissolved oxygen concentrations (DO) are 0-0.5 mL L−1 and accompanied by relatively high potential temperatures of 12.4 to 13.4 °C which can already be critical for CWC physiology. These present-day conditions prevent any CWC proliferation, and indeed no living colonies have been observed during the dives of a remotely operated vehicle.
After the analysis and discussion of the present-day environmental condition (Manuscript I), this thesis aimed to identify how oceanographic conditions controlled the spatial-morphological variability (Manuscript II) and temporal development (Manuscript III) of the Namibian coral mounds. The results show that spatial distribution and morphometric appearance of the coral mounds is highly controlled by the interplay between the underlying topography (erosional features) and the hydrodynamic regime (internal tides). Moreover, U-series dating on CWC skeletons combined with local paleoceanographic reconstructions link the temporal development (4.5-9.5 kyr BP) of the Namibian coral mounds to a decrease of the BUS activity, with a consequent relative relaxation of the local OMZ. This likely brought DO values comparable to the present-day hypoxic conditions on the Angola CMP, where living CWC colonies have been observed.
The findings of this thesis show how a comprehensive geological investigation on coral mounds can reveal important insights on the life and demise of CWC. The methods applied and the results obtained might serve as framework for investigating new CMPs, as well stimulating re-analyses of older datasets acquired from well-known CMPs. Moreover, improving our knowledge on CWC, to which this study on the Namibian coral mounds contributed, will provide insights on the fate of CWC under the changing ocean and climate conditions in the future.
... The NW Africa, offshore Mauritania, is where a coral mound province was mapped from the Tanoûdêrt Canyon at 20°15′N until close to the Senegalese border at 16°03′N (Figure 1) [39]. Through at least 580 km, the coral mounds represent one of the largest known complexes positioned in two-slope parallel chains and named Mauritanian Coral Province [29,32]. The coral mounds are on the bathymetrical range between 400 and 550 m depth and can achieve a height up to 100 m, supporting abundant associated species and live corals [30]. ...
... Small abundant outcrops of the barrier, which used to be a deep-water coral reef, are present at Timiris. This barrier is providing potential settlement ground for the proliferation of this species at the upper bathyal [11,29]. Local favorable factors to the growth of this octocoral may promote the monospecific coral garden predominance, despite the dormant state of the coral mounds [32]. ...
... Mauritania is a major upwelling region with a post-glacial oceanography less appropriate for reef-forming scleractinian development, in comparison with the oceanography during glacial times, or at the current northern latitudes [29,64]. ...
Swiftia Duchassaing & Michelotti, 1864, is often found sparse in the NE Atlantic Ocean and Mediterranean Sea. When the cruise MSM 16/3 “PHAETON” filmed the upper bathyal off Mauritania in 2010, the first dense populations dominated by Swiftia were discovered in the NE Atlantic Ocean, co-occurring with the framework-forming scleractinians Desmophyllum pertusum (Linnaeus, 1758) and Madrepora oculata Linnaeus, 1758. Remotely operated vehicle (ROV) video annotation from two canyons and two coral mounds considered Swiftia phaeton Sampaio, Beuck & Freiwald, 2022 presence, size class and abundance as well as substrate and geomorphology of the seafloor. Coral gardens definition included abundance and size of the species. Dense and very dense mono- and multispecific coral gardens dominated by S. phaeton were mapped between 20°24′N and 17°54′N in 470–640 m depth. The resilience of these coral gardens off Mauritania is mainly linked to the presence of hard substrate available to settle and to the exposition of currents rich in food. Still, these ecosystems are located inside a hydrocarbon exploration area off Mauritania and where fisheries occur since the 1960s. Sedimentation plumes caused by both activities can travel and impact on settlement, development, and survival of these populations. Hence, these vulnerable “oases” should be protected.
... Based on 3-dimensional seismic surveys of the Mauritanian EEZ by Woodside Mauritania Pty Ltd. between 1998, Colman et al. (2005 presented detailed maps of a cold-water coral mound barrier off Mauritania, at least 190 km long. The entire outer shelf and continental slope off Mauritania was later bathymetrically mapped between 150 and 2000 m, thus covering 31,300 km 2 , by the Spanish MAURIT Expeditions between 2007 and 2010 with the RV Vizconde de Eza (Ramos et al. 2017b, Sanz et al. 2017. These surveys showed the full lateral extension of the coral mound barrier to measure 405 km in length on the open slope. ...
... These surveys showed the full lateral extension of the coral mound barrier to measure 405 km in length on the open slope. The summits of the mounds are 300-600 m wide and found at approximately 450 m depth, whereas the bases are much wider reaching up to 2 km across (Ramos et al. 2017b). ...
... B ecause of the enrichment of marine waters due to upwelling, sediment transport by the easterly winds, and river inputs, the marine ecosystems off Mauritania and Senegal are particularly productive, containing a great biological diversity of algae, seagrass, invertebrates as well as abundant pelagic and demersal fishery resources. On the upper slope, subparallel to the shelf break, an extensive cold-water coral province is found, consisting of a series of cold-water coral reefs distributed from Cape Timiris (Mauritania) southwards into Senegalese waters extending for a distance of 400 km (Weinberg et al., 2018;Ramos et al., 2017). The reefs have been considered to be in a dormant state, deduced by ...
... The extensive cold-water coral province from Cape Timiris (Mauritania) southwards into Senegal, consists of a series of coral mounds, up to 100 m in height, which are arranged in two slope-parallel chains distributed over about 400 km. the observed current scarcity of living corals, the geological history, and the presence of an oxygen minimum zone (OMZ), until recent findings of rather large patches with living coral colonies (Colman et al., 2005;Ramos et al., 2017, Weinberg et al., 2018. ...
Thriving and highly diverse cold-water coral reefs were discovered and described in the GTA pipeline corridor and adjacent canyons during the recent survey with the R/V Dr. Fridtjof Nansen. The newly discovered reefs form a continuum with the Mauritanian mound barrier, the largest known coherent mound province in the world, and are therefore of local as well as global conservation interest. Predictive habitat modelling from the survey and the BP “Plume dispersion study” (2022) demonstrates that the suggested GTA pipeline route lies as far away as possible from any verified or modelled reefs and must therefore be considered the best choice from a sustainability viewpoint. However, there are large uncertainties associated with the plume dispersal model and furthermore, the sensitivity of local coral populations to suspended and settling sediments. Therefore, possible impacts of the pipeline constructions on corals’ state of health are difficult to predict. The dispersal model (BP, 2022) shows that there is a small (but real) risk of particles from the pipeline trenching work impacting the nearest coral reef (i.e. the Khairidine reef) either as suspended particles or settling particles.
... Distribution. This species is known to occur uniquely in the upper bathyal off Mauritania in deep-sea canyons and on deep-water coral mounds, where it lives in association with framework-forming species like Desmophyllum pertusum (Linnaeus, 1758) at the world largest known deep-water coral mound barrier (Ramos et al. 2017c;Wienberg et al. 2018). With the exception of the first ROV dive, Swiftia phaeton sp. ...
... This is particularly true considering the unexplored deep-sea areas, such as off northwest Africa, and taxa as Octocorallia, both of which lack taxonomical expertise. In Mauritania, the natural and human impact has already occurred in the form of depleted oxygen levels, sedimentation, demersal fisheries, and local oil exploration (Colman et al. 2005;Ramos et al. 2017c;Wienberg et al. 2018). Therefore, it is crucial to describe its diversity before it becomes extinct. ...
Three species of the genus Swiftia are known for the NE Atlantic Ocean and Mediterranean Sea. Remotely operated vehicle (ROV) surveys and sampling on board RV Maria S. Merian during cruise MSM 16/3 'PHAETON' in 2010 provided footage and specimens of octocorals off Mauritania. Micro-computed tomography (micro-CT) reveals, for the first time in taxonomy of octocorals, the three-dimensional arrangement of the sclerites in a polyp. Swiftia phaeton sp. nov. is described for the continental slope off Mauritania. This azooxanthellate octocoral is distinctive from NE Atlantic and Mediterranean congener-ics by the dark red colour of the colonies (including the polyps), the presence of a layer of rod sclerites on top of the polyp mounds, and different sizes of polyps and sclerites. Using micro-CT has allowed the observation and imaging of a layer of sclerites that is distinct from other species of the same genus. ROV images revealed live records of S. phaeton sp. nov. in submarine canyons and on cold-water coral mounds in the upper-bathyal off Mauritania (396-639 m depth), mainly attached to dead coral, coral rubble, or rocks. The new species represents an extension of the genus distribution to the tropical latitudes (17°07'N and 20°14'N) of the NE Atlantic Ocean.
... The objectives of most of these cruises included studying biological, oceanographic and geological aspects related to deep-water coral (DWC) habitats. New species of the genus Talassia were encountered in three areas: the Gulf of Mexico (Matos et al. 2017), off Mauritania (Ramos et al. 2017;Wienberg et al. 2018) and off Angola (Hebbeln et al. 2020). In 2007, the RV Poseidon cruise POS346 concentrated on the southern coral mound chain off Mauritania (Westphal 2007); sampling of two new species was conducted by box core. ...
... nov. have been found in upper bathyal oxygen minimum zones (OMZ) off western Africa (Westphal 2007;Westphal et al. 2014;Hebbeln et al. 2016Hebbeln et al. , 2020Ramos et al. 2017;Wienberg et al. 2018). Off Cape Blanc (NW Africa), the southward flowing Canary Current collides with the northward flowing Mauritanian current thereby forming the SW flowing Northern Equatorial Current (NEC). ...
A review was done on all species of the genus Talassia (family Vanikoridae Gray, 1840), which are known from an upper bathyal depth range in the Atlantic Ocean. Four new species are proposed: Talassia mexicana sp. nov. from the Gulf of Mexico, T. laevapex sp. nov. and T. flexisculpta sp. nov. from off Mauritania and T. rugosa sp. nov. from off Angola. Empty shells of the new species were found in sediment samples collected in habitats associated with deep-water corals. The new species were compared with the type species Talassia coriacea (Manzoni, 1868) and the deep-water species T. tenuisculpta (R.B. Watson, 1873), T. dagueneti (de Folin, 1873) and T. sandersoni (A.E. Verrill, 1884). Particularly the shape and sculpture of the protoconch show regional differences. Other specific characteristics are macro- and micro-sculpture of the teleoconch.
... Elle a par la suite fait l'objet de travaux lors des campagnes espagnoles Maurit et allemandes (Ramos et al., 2017a, b ;Westphal et al., 2012). La barrière qui s'étend du Cap Timiris à la frontière sénégalaise sur plus de 580 km constitue la plus grande structure de coraux d'eau froide connue au monde (Ramos et al., 2017c;Sanz et al., 2017a). ...
... Le composant principal est le corail d'eau froide Lophelia pertusa, ainsi que d'autres scléractiniaires, tels que Madrepora oculata et Dendrophyllia cornigera. Le déclin du récif qui a commencé après l'Holocène résulterait de conditions environnementales défavorables à la croissance des coraux et de l'épibenthos sessile associé (Ramos et al., 2017c ;Wienberg et al., 2018). Néanmoins, la barrière continue à jouer un rôle écologique très important sur le talus mauritanien en tant qu'élément déterminant de la répartition et de la séparation des assemblages côtiers et profonds (Ramos et al., 2017e). ...
During its ninth session, the working group was able to analyze all available data on the fisheries sector in Mauritania. A significant effort was dedicated to the validation, processing and analysis of available fisheries data. To capitalize on the expertise of participants, the following specialized committees were formed:
• Marine environment and biodiversity;
• Artisanal and continental fisheries;
• Pelagic fisheries;
• Demersal fisheries;
• Socioeconomic analyzes;
• Fisheries management.
Fisheries data and trends were analyzed and discussed by these committees or thematic groups in order to reach scientific assessments and recommendations for the preservation of marine resources and the marine environment leading to the development and sustainable management of fisheries.
With respect to the marine environment, data showed a gradual warming of coastal waters in Mauritania. This warming trend is likely related to the disturbances in the dynamics of the warm front which stays longer in Mauritanian waters. This warming trend is confirmed by data from the Cansado monitoring station where water daily temperature records for over three decades show that the seawater temperature rose by about 0.6 ° C on average.
Analysis of data from various national and international oceanographic campaigns has also shown an extension of the minimum oxygen zone (OMZ) to the Cap Blanc area, a situation that may affect the habitats of pelagic species.
In addition, a notable change in the direction of the prevailing winds was observed, going from NNW / NW for the period 1960-1999 to full north N from 2000 to 2018. This change undoubtedly influenced the dynamics of the upwelling which showed a decreased intensity in recent years.
Despite the industrial activities along the coastline and growing oil exploration activity, the marine and coastal environments (habitats and waters) remain relatively healthy and clean.
Description of fisheries
Artisanal fishing has undergone significant growth in recent decades. According to the latest IMROP framework survey, the pirogue fleet reached 6,800 boats in 2018, totaling a cumulative effort of 850,000 days at sea and 180,000 tonnes of catch.
Continental fishing remains seasonal, and primarily a subsistence activity by communities along the coast who rely on traditional means for fishing. Here, Mauritania has untapped potential that can be used in the fight against poverty and food insecurity. Recent institutional initiatives are aimed at improving the contribution of this sub-sector to the national economy.
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In the last decade, coastal fishing witnessed a very significant growth in these two components: "open canoe boat + 14m" and "decked vessels". Starting in 2011, the seine fishery gained importance underpinned by a booming milling industry. The implementation of the new fisheries strategy led to a significant exit of the open canoe (pirogue) fleet in 2016 and its replacement by vessels, some of which are of the RSW type. In 2018, these units reached about 100 distributed in the three segments: (Segment 1: Length less than 26m, Segment 2: Length between 26 and 40 m and Segment 3 Length between 40 and 60 m). These vessels mainly use seine, pelagic trawl and beef trawl (trawl is authorized only for segment 3).
Deep-sea fishing is practiced by different national and foreign fleets which comprise demersal and pelagic fishing vessels. The national fleet focuses mainly on cephalopods (in particular octopus). The number of deep-sea pelagic boats operating in Mauritanian waters (mostly foreign owned) has fluctuated in recent years averaging 50 vessels per year.
The number of boats targeting demersal resources reached 250 units in 2018 during which the effort of the cephalopod fleet reached 23,000 fishing days. The total cephalopod landing oscillated in recent years to an average of 40,000 tons of which more than 80% consists of octopus. In 2018, Octopus landings were 31,500 tons of which 11,400 tons were from deep-sea and coastal fishing and the rest from artisanal fishing.
The fishing effort by shrimp trawlers reached a maximum of 16,000 fishing days in 2002 before gradually declining until 2015 then improving in recent years. Catches followed a similar trend, with improved landings from 2017 to reach 2413 tons in 2018.
After a long suspension of pink lobster fishing, the Ministry of Fisheries (MPEM) authorized a trial fishing between 2015 and 2016 followed by open fishing in 2017. The number of lobster boats fluctuated between 2015 and 2018. Following a jump in effort, the catches of pink lobster dropped precipitously in 4 years, going from 704 tons in 2015 to 233 tons in 2018.
The number of hake fishing vessels in Mauritania fell from 45 in the 1990s to just 10 in 2018, yet the hake catches increased since 2013 to reach 14,000 tons in 2018.
The fishing effort varied greatly over the recent period, especially for the Spanish and Mauritanian vessels. In 2018, there were 500 fishing days for European/Spanish vessels versus 5,700 fishing days of effort for Mauritanian vessels. The catches increased significantly to reach over 14,000 t in 2018.
State of resources
Pelagic resources
Stock assessments of small pelagic show that Atlantic horse mackerel, round sardinella and ethmalose are in a state of overfishing. It was, therefore, recommended to take the necessary measures to reduce the fishing effort applied to these species. On the other hand, sardines and mackerel remain underexploited and can withstand additional fishing efforts. The total catches of small pelagics in the Mauritanian EEZ have steadily increased, sometimes exceeding one million tons per year.
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Demersal resources
The evaluation of the main demersal resources shows that these resources are either underexploited (cuttlefish, squid and shrimps) or fully exploited (octopus, hake) or overexploited (pink lobster). The other types of demersal fish were not the subject of a specific assessment; however, their abundance indices have declined in 2017 and 2018.
The octopus stock has recovered from a state of overexploitation under an excess effort of 17% (working group 2014) to a state of full/optimum exploitation in 2018. This situation is the result of the combination of several efforts, including a seasonal halt of fishing to allow recovery of octopus stocks and a gradual reduction in fishing pressure. It was recommended that extreme caution be observed in the exploitation of this stock, which is still weakened by long years of overfishing. Species such as cuttlefish and squid offer alternative exploitation possibilities as their potential has been revised upwards in line with abundance indices.
Exploitable potential
The Working Group estimated that the fishery resources in the Mauritanian economic zone has 1,830,140 tonnes of fishing potential, all species combined. These estimates confirm the potential economic value of the exploitable Mauritanian fisheries which are diverse with an estimated nearly 97,000 tons/year of demersal fich, 7,440 tons of crustaceans, 42,700 tons of cephalopods (Octopus, Sepia and Squid), and 1,383,000 tons/year of pelagic resources. The potential of bivalve mollusks (especially Venus) is in the order of 300,000 tons per year. The bivalve mollusk stock is not currently being exploited for market demand reasons.
Sustainable fisheries management
The sustainable management plan for the octopus stock (strategic resource) was adopted by the ministry of fisheries (MPEM) under decree (R0764/MPEM of 10/10/2018) following rigorous validation processes. The validation processes were based on the establishment of an institutional framework for consultation according to participatory approaches, integrating the various stakeholders and based on the opinion of the National Advisory Council for Fisheries Planning and Development (CCNADP).
Socio economic analyzes
The socio-economic impact of the fisheries sector have improved significantly in recent years. Fishery landings are currently in the order of 700,000 tons per year, or 60% of the catches taken in the ZEEM, leading to near doubling of the annual treasury revenues.. The fishery sector's overall exports reached more than US$1 billion, making fishing the largest export sector by value for Mauritania.
Jobs generated by the fisheries sector were estimated using a consolidated approach based on objective criteria and reliable models. It is estimated that the sector currently generates 226,000 jobs (direct and indirect), excluding jobs generated by the river and continental fishery.
The added value of "fishing" has grown steadily in recent years. It rose from MRU 2.9 billion in 2014 to MRU 6.2 billion in 2018. This increase boosted the share of fisheries in the
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country’s primary sector GDP from 7.1% in 2015 to 13.3% in 2018. The sector's contribution to total Mauritanian GDP has also experienced the same upward trend, rising from 1.8% in 2015 to 3.3% in 2018.
Major private investments in the fishery sector reached MRU 13.5 billion in 2018 or about US$370 million. This represents US$105 million more than the target set by the fisheries growth strategy for 2019/2020.
The number of licensed factories increased from 68 in 2013 to 149 in 2018, thereby increasing the processing and storage capacity of fish products from 20,000 tons in 2013 to 70,000 tons in 2018 or an increase of more than 300%.
During the same period, the national per capita consumption increased from an average of around 10 kg in 2014 to 12.6 kg/h/year in 2018.
... Information about CWC reefs off North Atlantic Africa in areas that are dominated by a broad oxygen minimum zone (OMZ) has been provided by Colman et al. (2005), Krastel et al. (2006), Eisele et al. (2011), Buhl-Mortensen et al. (2017a, Ramos et al. (2017), Wienberg et al. (2018Wienberg et al. ( , 2023, Portilho-Ramos et al. (2022), and Buhl- Mortensen et al. (2023). Along the Mauritanian continental margin, a 400-km-long almost continuous CWC mound chain has been investigated by several surveys that reported only few live colonies from the mounds that stopped growing 10.000 years ago (Wienberg et al., 2018(Wienberg et al., , 2023. ...
The occurrence of cold-water coral (CWC) reefs off Northwest Africa that has a broad oxygen minimum zone (OMZ) is poorly studied. A 400 km long almost continuous coral mound chain off Mauritania that was investigated by earlier expeditions revealed mainly dead corals. In 2021, the EAF-Nansen Programme conducted a survey at the border between Mauritania and Senegal with the main objective to map CWCs. Acoustic mapping with multibeam echosounder was used to target mounds at 450-650 m depth and 14 video lines were conducted using a remotely operated vehicle (ROV). The occurrence and health status of CWC reefs along video transects were annotated using the software "CampodLogger", oceanographic variables were measured using a CTD sonde, and terrain and backscatter analysis were conducted. Here we present the environment and health status of 13 Lophelia reefs established in the study area, six of them were large and healthy reefs with areas having 15-50% cover of live colonies. Oxygen concentrations were measured to be as low as 1 ml L − 1 and temperature ranged from 8.8 to 11.6 • C. We compare reef health with the environmental variables: temp, salinity, oxygen, and particle load. A GIS based model was developed to predict the occurrence of live reefs in the study area based on the observed average range of a set of terrain descriptors measured where live Lophelia reefs occurred. Our findings of healthy Lophelia reefs are unexpected and further north in the OMZ reefs have been described as dormant. There is an urgent need for visual seafloor mapping to aid the development of spatial management plans in these understudied waters.
... Biogenic mounds have developed in a wide depth range, from coastal areas to deeper environments (> 1,000 m), and they can be formed by a variety of organisms. The dimensions and shapes of mounds may vary a lot, with heights ranging from a few meters to > 300 m, and lateral extensions of up to tens of kilometers (Ramos et al., 2017;Wienberg et al., 2018;Hebbeln et al., 2019). The bioconstructions are normally grouped into provinces, which may comprise tens to hundreds of individual mounds (Hebbeln et al., 2014;Glogowski et al., 2015). ...
The mesophotic domain is a poorly explored part of the oceans, notably in the Mediterranean Sea. Benthic communities in these depths are not well documented and as such are under higher risk from anthropogenic impacts. Hard substrate habitats in this depth window are not common and are a key ecotope. The Malta Plateau in the central Mediterranean, which is characterized by low sedimentation rates, offers a potentially unexplored domain for these features. Bathymetric and backscatter data offshore of the eastern coast of the island of Malta were used to identify > 1,700 small structures in mesophotic depths. These structures were verified to be biogenic mounds by dives. The mounds extend from several meters to tens of meters in diameter and occur in two main depth windows −40 to 83 meters below present sea level (mbpsl) and 83–120 mbpsl—each formed probably in a different stage during the last glacial cycle. The mounds are composed of interlocking bioconstruction by encrusting organisms and are colonized by sponges and various cold water corals (most of which are protected; e.g., Madrepora oculata). This unique and important habitat is currently under grave threat by human activity, most immediately by trawling and anchoring activity.
... Biogenic mounds have developed in a wide depth range, from coastal areas to deeper environments, and they can be formed by a variety of organisms. The dimensions and shapes of mounds may vary a lot, with heights ranging from a few metres to >300 m, and lateral extensions of up to tens of kilometers (Ramos et al., 2017;Wienberg et al., 2018;Hebbeln et al., 2019). The bioconstructions are normally grouped into provinces, which may comprise tens to hundreds of individual mounds (Hebbeln et al., 2014;Glogowski et al., 2015). ...
The mesophotic domain is a poorly explored part of the oceans, notably in the Mediterranean Sea. Benthic communities in these depths are not well documented and as such are under higher risk from anthropogenic impacts. Hard substrate habitats in this depth window are not common and are a key ecotope. The Malta Plateau in the central Mediterranean, which is characterised by low sedimentation rates, offers a potentially unexplored domain for these features. Bathymetric and backscatter data offshore of the eastern coast of the island of Malta were used to characterise the benthic habitats. >1700 small structures were identified in mesophotic depth and verified by dives to be biogenic mounds. These mounds extend from several meters to tens of meters in diameter and occur in two main depth windows 40 to 83 mbpsl and 83 to 120 mbpsl, each formed probably in a different stage along the last glacial cycle. The mounds are composed of interlocking bioconstruction by encrusting organisms and are colonised by sponges and various cold water corals (most of which are protected). This unique and important habitat is currently under grave threat by human activity, most immediately by trawling activity.
... Despite a surface area fourfold smaller than seagrass beds, coral reefs' unit value is much higher thanks to their highly valued control in erosion rates and their support to activities promoting health, recuperation or enjoyment through active or immersive interactions. Cold-water corals, that were omitted in this valuation, are also largely represented in West Africa (Hebbeln et al., 2019;Ramos et al., 2017;Yesson et al., 2012), and provide habitat and refuge for many fish of commercial value and invertebrates. Support of commercial fisheries probably represents the most important services offered by cold-water corals (Foley et al., 2010). ...
The African coastline is bordered by highly valuable marine ecosystems, but the environmental degradation due to anthropogenic pressure alter the benefits that they render to people. Our paper aims at assessing the value of ecosystem services provided by mangroves, seagrass beds, coral reefs, and kelp forests present in the Large Marine Ecosystems (LMEs) of Africa. After the mapping of coastal marine habitats, our valuation relies on the transfer of value of all ecosystem services from reference monetary unit values, extracted from the literature. A habitat function-ality index based on the assumption that a higher population density and a higher demographic growth rate lead to a decrease in the functionality and services of marine habitats was then defined and incorporated into the valuation. The surveyed coastal habitats cover about 117,000 km2, with seagrass beds being by far the most extensive habitat. Present all along the coasts of Africa, their surface area represents about 62% of surveyed coastal habitats, followed by the mangroves (23%), coral reefs (15%). Kelp forests are only present in the southern Benguela Current LME. We estimated the annual value of the LME’s coastal ecosystem services at 814 billion USD. Coral reefs have the highest value (588 billion USD/year), followed by seagrass beds (135 billion USD/year), mangroves (91 billion USD/year), and kelp forests (0.4 billion USD/ year). The results show that ecosystem services from the four coastal habitat types had the highest value in the Agulhas Current LME, representing 38% of the total value, followed by the Red Sea LME (28%) and the Somali Coastal Current LME (10%). The three LMEs of the Atlantic side represent 15% of the total estimated value. Our paper highlighted many gaps that remain to be filled in terms of mapping and ecosystem services assessment in Africa. Nonetheless, our esti-mated values can facilitate dialogue between decision-makers and managers, and between countries sharing the same habitats and marine resources, toward better management of these ecosystems.
... psu Davies et al., 2008), dissolved oxygen 1.0-7.2 ml l −1 (Dodds et al., 2007;Davies et al., 2008Davies et al., , 2010Ramos et al., 2017), and sigma-theta 27.35-27.6 kg m −3 (in the eastern Atlantic) (Dullo et al., 2008). ...
Cold-water coral (CWC) communities form complex benthic ecosystems in a distinct part of the water column. The exact processes supporting CWC reef growth and changes with time are still partly unsolved. Besides local hydrographic conditions, noticeable interactions of tidal flow with topography have been reported for CWC sites. Recent studies have suggested a tidally driven hydraulic control of flow over topographic features as a driver for local overturning at cold-water coral sites. This mechanism proposed a link between surface productivity and coral growth depths and is a driver of resuspension of the bottom material. Only few studies have concentrated on how these processes vary with the health status and structure of the cold-water coral occurrences. In this study, we explore the processes over tidal cycles by analyzing in situ stratification, hydrography and velocity data which we then combine with local topography from seven Desmophyllum pertusum (previously Lophelia pertusa) dominated eastern Atlantic CWC sites, from the Arctic to the southern hemisphere. The “quality” of CWC sites varies from thriving to declining and dead reefs. We show that living and healthy corals are concentrated at sites, where local hydrodynamics create overturning and mixing which overcomes on a daily basis gravitational particle sinking and thus re-supply food to filter-feeding corals. We find a very wide range of local hydrographic and biogeochemical conditions at the sites which suggests they play only a secondary role for CWC health.
... In addition, the majority of occurrences of live L. pertusa comes from sites with dissolved oxygen (DO) concentrations between 6 and 6.5 mL L −1 (Davies et al., 2008), with lowest recorded oxygen values being 2.1-3.2 mL L −1 at CWC sites in the Gulf of Mexico (Davies et al., 2010;Schroeder, 2002;Brooke and Ross, 2014) or even as low as 1-1.5 mL L −1 off Mauritania, where CWC mounds are in a dormant stage presently showing only scarce living coral occurrences (Wienberg et al., 2018;Ramos et al., 2017). Dissolved oxygen levels hence seem to affect the formation of CWC structures as was also shown by Holocene records obtained from the Mediterranean Sea, which revealed periods of reef demise and growth in conjunction with hypoxia (with 2 mL L −1 seemingly forming a threshold value for active coral growth; Fink et al., 2012). ...
Thriving benthic communities were observed in the oxygen minimum zones along the southwestern African margin. On the Namibian margin, fossil cold-water coral mounds were overgrown by sponges and bryozoans, while the Angolan margin was characterized by cold-water coral mounds covered by a living coral reef. To explore why benthic communities differ in both areas, present-day environmental conditions were assessed, using conductivity–temperature–depth (CTD) transects and bottom landers to investigate spatial and temporal variations of environmental properties. Near-bottom measurements recorded low dissolved oxygen concentrations on the Namibian margin of 0–0.15 mL L−1 (≜0 %–9 % saturation) and on the Angolan margin of 0.5–1.5 mL L−1 (≜7 %–18 % saturation), which were associated with relatively high temperatures (11.8–13.2 ∘C and 6.4–12.6 ∘C, respectively). Semidiurnal barotropic tides were found to interact with the margin topography producing internal waves. These tidal movements deliver water with more suitable characteristics to the benthic communities from below and above the zone of low oxygen. Concurrently, the delivery of a high quantity and quality of organic matter was observed, being an important food source for the benthic fauna. On the Namibian margin, organic matter originated directly from the surface productive zone, whereas on the Angolan margin the geochemical signature of organic matter suggested an additional mechanism of food supply. A nepheloid layer observed above the cold-water corals may constitute a reservoir of organic matter, facilitating a constant supply of food particles by tidal mixing. Our data suggest that the benthic fauna on the Namibian margin, as well as the cold-water coral communities on the Angolan margin, may compensate for unfavorable conditions of low oxygen levels and high temperatures with enhanced availability of food, while anoxic conditions on the Namibian margin are at present a limiting factor for cold-water coral growth. This study provides an example of how benthic ecosystems cope with such extreme environmental conditions since it is expected that oxygen minimum zones will expand in the future due to anthropogenic activities.
... Subsequently, the empirically obtained ranges of individual environmental parameters have been interpreted as generally valid thresholds controlling the occurrence of CWC on a global scale (Davies and Guinotte, 2011). However, recent discoveries of hitherto unknown CWC reefs that exist today under rather "extreme" conditions [e.g., in terms of temperature or oxygen (Ramos et al., 2017)], force us to shift the upper and lower thresholds of environmental parameters beyond formerly described values. In addition, laboratory experiments conducted on several common CWC species (e.g., Lophelia pertusa, Madrepora oculata, and Dendrophyllia) provided additional information on their ecological requirements (e.g., in terms of temperature, carbonate system, food supply, and oxygen) (e.g., Tsounis et al., 2010;Gori et al., 2014;Movilla et al., 2014;Naumann et al., 2014;Maier et al., 2016;Büscher et al., 2017) and also indicate region-specific adaptations of CWC to particular environmental parameters (Dodds et al., 2007;Lunden et al., 2014). ...
As “ecosystem engineers,” framework-forming scleractinian cold-water corals (CWC) build reefs that are unique biodiversity hotspots in the deep sea. Studies using common biological techniques such as correlating the spatial occurrence of the most common CWC species with modeled environmental conditions have revealed the ecological requirements and tolerances of these species. However, limited field observations and poorly understood geographical distribution patterns of the CWC restrict the application of existing knowledge toward assessing their fate (e.g., local extinction, newly established populations) under ongoing global change. Hence, the risk to cross ecological tipping points causing the demise (or establishment) of entire CWC reefs remains unclear. A major challenge is to identify the key environmental parameters (or stressors) having the potential to control CWC vitality by providing such tipping points. This is largely hampered by the overall lack of present-day observations of such tipping point crossings. However, evidence for such events is frequently preserved in geological records revealing that entire CWC ecosystems vanished or returned at specific moments in the past. Here, a geological approach is presented that by correlating geological CWC records with paleoceanographic data describing past environmental changes allows to identify a set of key environmental drivers that directly or indirectly control CWC vitality. Thus, by combining such a geological approach with common biological techniques (see above) to describe the ecological tolerance of the most important reef-building CWC has a great potential to better assess their future spatial distribution in times of accelerating global change and to improve the sustainable management of the important deep-sea ecosystems formed by CWC.
... A total of 342 stations were sampled from 80 to 2000 m depth off Mauritanian coast, between Cape Blanc in the north and the Senegalese border in the south, including the Banc d'Arguin and the giant cold-water coral mounds barrier running parallel to the shelf break along the Mauritanian slope south to Cape Timiris (Ramos et al., 2017c). Of these, 316 stations were sampled over the soft bottom on the deep-shelf and slope using a commercial trawl (291 stations) and a beam trawl (25 stations). ...
This paper deals with species of the deep-water marine lobsters and lithodids collected on soft and rocky bottoms during the four Spanish Maurit surveys from 2007 to 2010 in Mauritanian waters, at depths between 80 and 2000 m. The collection is represented by eight species included in the infraorders Astacidea, Achelata, and Polychelida, and by five species of the family Lithodidae. The true lobster Nephropsis atlantica, the blind lobster Stereomastis nana, and the king crab Paralomis cristulata are reported for the first time in Mauritanian waters, while the presence of the slipper lobster Scyllarus subarctus is confirmed in the area. New data on the bathymetric distribution of P. cristulata and Lithodes ferox are also included.
Large, well-developed and flourishing reefs dominated by the cold-water coral Desmophyllum pertusum have recently been discovered along the Angola margin in the southeastern Atlantic Ocean living under very low oxygen concentrations (0.6–1.5 mL L− 1). This study assessed the respiration rates of this coral in a short-term (10 days) aquarium experiment under naturally low oxygen concentrations (1.4 ± 0.5 mL L− 1) as well as under saturated oxygen concentrations (6.1 ± 0.6 mL L− 1). We found no significant difference in respiration rates between the two oxygen concentrations. Furthermore, the respiration rates of D. pertusum were in the same order of magnitude as those of the same species living under normoxic conditions in other areas. This work expands the current knowledge on the metabolic activity of cold-water corals under hypoxic conditions, evidencing that low oxygen conditions are not a general limiting factor for the overall distribution of D. pertusum.
The start-up, build-up and demise of cold-water coral mounds are governed by environmental changes at global, regional and local scales. Whilst the formation of cold-water coral mounds across the globe is widely documented to follow interglacial-glacial cycles, less is known about their response to local environmental fluctuations during short time intervals. This study investigates the local variations in coral mound build-up along Brittlestar Ridge I (East Melilla Coral Province, Southeast Alboran Sea) by comparing three on-mound gravity cores collected ~1 km apart, together with five previously described on-mound records, along a longitudinal transect on the ridge crest. Radiocarbon foraminiferal dating associated to U-series coral dating allowed to correlate the different records and to estimate mound aggradation rates, whilst grain-size analysis provided information on bottom current velocities. Prior to a rapid period of coral mound build-up initiated at ~14.75 ka BP, the three cores present an occurrence of cm-thick bryozoan-dominated intervals nearly entirely consisting of the erect cheleis-tome Buskea dichotoma. Offsets between benthic foraminiferal and coral ages suggest that older dead allochto-nous benthic foraminifera are possibly eroded from neighbouring settings, transported and deposited within the coral framework. In contrast, younger benthic foraminifera would develop on dead coral framework during periods of reef stagnation. The comparison of all cores indicates that mound build-up along the ridge did not follow the same timing during the last ~16 kyr and that mound aggradation was marked by a staggered dynamic. Both local differences in bottom current velocities and patchiness of other key environmental actors (e.g. sub-strate availability) are suspected to drive the observed staggered mound build-up. Cold-water coral mound build-up shows important differences during Greenland Interstadial 1 (i.e. the Bølling-Allerød) and the Holocene, hence examplifying how local environmental variability may overprint global and regional climate variability over short time periods.
Cold-water corals (CWCs) are the engineers of complex ecosystems forming unique biodiversity hotspots in the deep sea. They are expected to suffer dramatically from future environmental changes in the oceans such as ocean warming, food depletion, deoxygenation, and acidification. However, over the last decades of intense deep-sea research, no extinction event of a CWC ecosystem is documented, leaving quite some uncertainty on their sensitivity to these environmental parameters. Paleoceanographic reconstructions offer the opportunity to align the on- and offsets of CWC proliferation to environmental parameters. Here, we present the synthesis of 6 case studies from the North Atlantic Ocean and the Mediterranean Sea, revealing that food supply controlled by export production and turbulent hydrodynamics at the seabed exerted the strongest impact on coral vitality during the past 20,000 years, whereas locally low oxygen concentrations in the bottom water can act as an additional relevant stressor. The fate of CWCs in a changing ocean will largely depend on how these oceanographic processes will be modulated. Future ocean deoxygenation may be compensated regionally where the food delivery and food quality are optimal.
This study aims to map the occurrence and distribution of Madrepora oculata and to quantify density and colony sizes across recently discovered coral mounds off Angola. Despite the fact that the Angolan populations of M. oculata thrive under extreme hypoxic conditions within the local oxygen minimum zone, they reveal colonies with remarkable heights of up to 1250 mm—which are the tallest colonies ever recorded for this species—and average densities of 0.53 ± 0.37 (SD) colonies m−2. This is particularly noteworthy as these values are comparable to those documented in areas without any oxygen constraints. The results of this study show that the distribution pattern documented for M. oculata appear to be linked to the specific regional environmental conditions off Angola, which have been recorded in the direct vicinity of the thriving coral community. Additionally, an estimated average colony age of 95 ± 76 (SD) years (total estimated age range: 16–369 years) indicates relatively old M. oculata populations colonizing the Angolan coral mounds. Finally, the characteristics of the Angolan populations are benchmarked and discussed in the light of the existing knowledge on M. oculata gained from the North Atlantic and Mediterranean Sea.
Surface benthic foraminiferal assemblages associated with cold‐water coral mounds and reefs from the Irish margin and Norwegian shelf (North‐east Atlantic) are for the first time compared quantitatively. Results indicate that the considered sites share a common assemblage, dominated by elevated epibenthic and distinct infaunal species. This surface assemblage is typical of environments that are subject to strong bottom‐water turbulence with enhanced food availability. It provides a benchmark for comparison with fossil benthic foraminiferal assemblages from past cold‐water coral environments. Similar to macrofaunal and megafaunal communities, surface benthic foraminiferal diversity is higher on reefs and mounds than in surrounding off‐mound/off‐reef sediments. Benthic foraminiferal diversity is highest within the living coral macrohabitat, possibly as a result of enhanced availability and variety of food sources, and ecological niche separation. Indeed, living coral generally thrives on the summits or flanks of reefs and mounds where food availability is most important. The second part discusses the use of fossil benthic foraminiferal assemblages as palaeoceanographic proxies from past cold‐water coral environments. The overview of previous observations demonstrates that benthic foraminifera are valuable tools to reconstruct past bottom‐water oxygenation, bottom‐water currents and surface productivity, all of which are key environmental variables controlling cold‐water coral growth. Moreover, the advantages of a detailed investigation of benthic foraminiferal assemblages within cold‐water coral environments are compared to other palaeoceanographic proxies. This study highlights that benthic foraminiferal assemblages are an often overlooked proxy within cold‐water coral environments, despite yielding valuable information.
It is proposed to name the Atlantic holothuria Psolidium complanatum Cherbonnier, 1969, whose denomination is already occupied by Psolidium complanatum (Semper, 1867) from the Philippines, as Psolidium bathygalego nom. nov. 843 specimens of Psolidium bathygalego nom. nov., collected between 417 and 1191mdeep in the NW and W of Galicia and in the Galicia Bank, were studied. A detailed description of the external and internal anatomy of Psolidium bathygalego nom. nov. is made by studying the ossicles and the skeletal structure by means of scanning electron microscopy (SEM) as well as the introvert, calcareous ring, retractor muscles, watervascular system, digestive system, respiratory trees, and reproductive system by means of micro-computed tomography (micro-CT). The habitat, feeding system, and geographical distribution of Psolidium bathygalego nom. nov. are also described.
Multidisciplinary surveys conducted on-board RV Dr Fridtjof Nansen in the northwest Africa region during November 2011 and June 2012 allowed exploration for the first time of seasonal variations in diversity and structure of decapod communities inhabiting the changing hydrological scenario of the shelf and upper slope off Mauritania (20–750 m depth). Decapods were gathered with a commercial bottom trawl at 95 stations, 39 of which were visited in both surveys. In addition, 249 oceanographic profiles and 95 sediment samples were collected. Shelf and slope assemblages, respectively characterized by the dominance of benthic (63 species) and swimming decapods (37 species), were segregated at 100–150 m depth, coinciding with the shelf-break and the hydrological frontier separating the surface mixed layer from the deeper water masses. The assemblages showed a certain stability in their structure but significant seasonal differences in their composition. Abundance and biomass, and in particular specific richness, were strongly correlated with depth in the case of swimming decapods, which were clearly dominant during the warm season, especially in the southern zone. The most significant seasonal variations were mainly due to the Penaeidae family and its associated species, Parapenaeus longirostris (Lucas, 1846). The latitudinal decreasing trend in upwelling permanence and productivity toward the south, responding to the strength and displacement of trade winds along the Mauritanian coast, which are observable at the surface and sea-bottom, were the main reason explaining the seasonal variations observed in the distribution patterns and assemblages structure of Mauritania decapods.
Reefs formed by scleractinian cold-water corals represent unique biodiversity hot spots in the deep sea, preferring aphotic water depths of 200–1000 m. The distribution of the most prominent reef-building species Lophelia pertusa is controlled by various environmental factors including dissolved oxygen concentrations and temperature. Consequently, the expected ocean deoxygenation and warming triggered by human-induced global change are considered as a serious threat to cold-water coral reefs. Here, we present results on recently discovered reefs in the SE Atlantic, where L. pertusa thrives in hypoxic and rather warm waters. This sheds new light on its capability to adapt to extreme conditions, which is facilitated by high surface ocean productivity, resulting in extensive food supply. Putting our data in an Atlantic-wide perspective clearly demonstrates L. pertusa’s ability to develop population-specific adaptations, which are up to now hardly considered in assessing its present and future distributions.
Three species in the gastropod genus Calliostoma are confirmed as living in Deep-Water Coral (DWC) habitats in the NE Atlantic Ocean: Calliostoma bullatum (Philippi, 1844), C. maurolici (Seguenza, 1876) and C. leptophyma Dautzenberg & Fischer, 1896. Up to now, C. bullatum was only known as fossil from Early to Mid-Pleistocene outcrops in DWC-related habitats in southern Italy; our study confirmed its living presence in DWC off Mauritania. A discussion is provided on the distribution of DWC-related calliostomatids in the NE Atlantic and the Mediterranean Sea from the Pleistocene to the present.
Aim
To infer cold‐water corals’ (CWC) post‐glacial phylogeography and assess the role of Mediterranean Sea glacial refugia as origins for the recolonization of the northeastern Atlantic Ocean.
Location
Northeastern Atlantic Ocean and Mediterranean Sea.
Taxon
Lophelia pertusa, Madrepora oculata.
Methods
We sampled CWC using remotely operated vehicles and one sediment core for coral and sediment dating. We characterized spatial genetic patterns (microsatellites and a nuclear gene fragment) using networks, clustering and measures of genetic differentiation.
Results
Inferences from microsatellite and sequence data were congruent, and showed a contrast between the two CWC species. Populations of L. pertusa present a dominant pioneer haplotype, local haplotype radiations and a majority of endemic variation in lower latitudes. Madrepora oculata populations are differentiated across the northeastern Atlantic and genetic lineages are poorly admixed even among neighbouring sites.
Conclusions
Our study shows contrasting post‐glacial colonization pathways for two key habitat‐forming species in the deep sea. The CWC L. pertusa has likely undertaken a long‐range (post‐glacial) recolonization of the northeastern Atlantic directly from refugia located along southern Europe (Mediterranean Sea or Gulf of Cadiz). In contrast, the stronger genetic differentiation of M. oculata populations mirrors the effects of long‐term isolation in multiple refugia. We suggest that the distinct and genetically divergent, refugial populations initiated the post‐glacial recolonization of the northeastern Atlantic margins, leading to a secondary contact in the northern range and reaching higher latitudes much later, in the late Holocene. This study highlights the need to disentangle the influences of present‐day dispersal and evolutionary processes on the distribution of genetic polymorphisms, to unravel the influence of past and future environmental changes on the connectivity of cosmopolitan deep‐sea ecosystems associated with CWC.
Fossil cold-water coral mounds overgrown by sponges and bryozoans were observed in anoxic conditions on the Namibian margin, while mounds colonized by thriving cold-water coral reefs were found in hypoxic conditions on the Angolan margin. These low oxygen conditions do not meet known environmental ranges favoring cold-water corals and hence are expected to provide unsuitable habitats for cold-water coral growth and therefore reef formation. To explain why the living fauna can nevertheless thrive in both areas, present day environmental conditions at the southwestern African margin were assessed. Downslope CTD transects and the deployment of bottom landers were used to investigate spatial and temporal variations of environmental properties. Temporal measurements in the mound areas recorded oscillating low dissolved oxygen concentrations of 0–0.17 ml l−1 (≙ 0–9 % saturation) on the Namibian and 0.5–1.5 ml l−1 (≙ 7–18 % saturation) on the Angolan margin, which were associated with relatively high temperatures (11.8 13.2 °C and 6.4–12.6 °C respectively). Semi-diurnal barotrophic tides were found to interact with the margin topography producing internal waves with excursions of up to 70 and 130 m for the Namibian and Angolan margins, respectively. These tidal movements temporarily deliver water with more suitable characteristics to the coral mounds from below and above the hypoxic zone. Concurrently, the delivery of high quantity and quality of suspended particulate organic matter was observed, which serves as a food source for cold-water corals. On the Namibian slope organic matter indicates a completely marine source and originates directly from the surface productive zone, whereas on the Angolan margin the geochemical signature of organic material suggest an additional mechanisms of food supply. A nepheloid layer observed above the cold-water coral mound area on the Angolan margin may constitutes a reservoir of fresh organic matter, facilitating a constant supply of food particles by tidal mixing. This suggests that the cold-water coral communities as well as the associated fauna may compensate unfavorable conditions induced by low oxygen levels and high temperatures with an enhanced availability of food. With the expected expansion of oxygen minimum zones in the future due to anthropogenic activities, this study provides an example on how ecosystems could cope with such extreme environmental conditions.
We investigated how interactions between hydrography, topography and species ecology influence the assembly of species and functional traits across multiple spatial scales of a cold-water coral reef seascape. In a novel approach for these ecosystems, we used a spatially resolved complex three-dimensional flow model of hydrography to help explain assembly patterns. Forward-selection of distance-based Moran's eigenvector mapping (dbMEM) variables identified two submodels of spatial scales at which communities change: broad-scale (across reef) and fine-scale (within reef). Variance partitioning identified bathymetric and hydrographic gradients important in creating broad-scale assembly of species and traits. In contrast, fine-scale assembly was related more to processes that created spatially autocorrelated patches of fauna, such as philopatric recruitment in sessile fauna, and social interactions and food supply in scavenging detritivores and mobile predators. Our study shows how habitat modification of reef connectivity and hydrography by bottom fishing and renewable energy installations could alter the structure and function of an entire cold-water coral reef seascape.
There are more coral species in deep, cold-waters than in tropical coral reefs. This broad-ranging treatment is the first to synthesise current understanding of all types of cold-water coral, covering their ecology, biology, palaeontology and geology. Beginning with a history of research in the field, the authors describe the approaches needed to study corals in the deep sea. They consider coral habitats created by stony scleractinian as well as octocoral species. The importance of corals as long-lived geological structures and palaeoclimate archives is discussed, in addition to ways in which they can be conserved. Topic boxes explain unfamiliar concepts, and case studies summarize significant studies, coral habitats or particular conservation measures. Written for professionals and students of marine science, this text is enhanced by an extensive glossary, online resources, and a unique collection of color photographs and illustrations of corals and the habitats they form. © J. Roberts, A. Wheeler, A. Freiwald and S. Cairns 2009 and Cambridge University Press, 2009.
Over the last twenty years, human exploitation has begun to have an impact in the deep sea, especially in the upper bathyal zone. This has mainly taken the form of deep-sea fishing but more recently oil exploration has extended beyond the continental shelf. Deep-water coral reefs occur in the upper bathyal zone throughout the world. These structures, however, are poorly studied with respect to their occurrence, biology and the diversity of the communities associated with them. In the North-East Atlantic the coral Lophelia pertusa has frequently been recorded. The present review examines the current knowledge on L. pertusa and discusses similarities between its biology and that of other deep-water, reef-forming, corals. It is concluded that L. pertusa is a reef-forming coral that has a highly diverse associated fauna. Associated diversity is compared with that of tropical shallow-water reefs. Such a highly diverse fauna may be shared with other deep-water, reef-forming, corals though as yet many of these are poorly studied. The main potential threats to L. pertusa in the North-East Atlantic are considered to be natural phenomena, such as slope failures and changes in ocean circulation and anthropogenic impacts such as deep-sea fishing and oil exploration. The existing and potential impacts of these activities on L. pertusa are discussed. Deep-sea fishing is also known to have had a significant impact on deep-water reefs in other parts of the world.
General paradigms of species extinction risk are urgently needed as global habitat loss and rapid climate change threaten Earth with what could be its sixth mass extinction. Using the stony coral Lophelia pertusa as a model organism with the potential for wide larval dispersal, we investigated how the global ocean conveyor drove an unprecedented post-glacial range expansion in Earth׳s largest biome, the deep sea. We compiled a unique ocean-scale dataset of published radiocarbon and uranium-series dates of fossil corals, the sedimentary protactinium-thorium record of Atlantic meridional overturning circulation (AMOC) strength, authigenic neodymium and lead isotopic ratios of circulation pathways, and coral biogeography, and integrated new Bayesian estimates of historic gene flow. Our compilation shows how the export of Southern Ocean and Mediterranean waters after the Younger Dryas 11.6 kyr ago simultaneously triggered two dispersal events in the western and eastern Atlantic respectively. Each pathway injected larvae from refugia into ocean currents powered by a re-invigorated AMOC that led to the fastest postglacial range expansion ever recorded, covering 7500 km in under 400 years. In addition to its role in modulating global climate, our study illuminates how the ocean conveyor creates broad geographic ranges that lower extinction risk in the deep sea.
Deep-water coral reefs are found along large sections of the outer continental shelves and slopes of Europe, from North Cape to the Gulf of Cadiz, and because they also occur along the Atlantic seaboard of USA, the Gulf of Mexico, off Brazil, in the Mediterranean, and off New Zealand, they are currently being targeted by international groups of marine scientists. They have become popular and opportune deep-water research targets because they offer exciting frontier exploration, combined with a whole plethora of modern scientific methods, such as deep-sea drilling, sampling, remote control surveying and documentation. Furthermore they represent timely opportunities for further developments within the application of geochemistry, stable isotope research, bacterial sciences, including DNA-sequestering, and medical research (search for bioactive compounds).
The Integrated Ocean Drilling Program (IODP) has arranged a deep-sea scientific drilling campaign on giant carbonate banks off Ireland. Because the reefs currently defy traditional marine-ecological theories, they represent future research opportunities and will enjoy scientific scrutiny for many years to come.
In this study the distributional pattern of the macro- and megafauna of a small (ca. 300 m(2)) Lophelia pertusa (L., 1758) reef was studied with a ROV (remotely operated vehicle). The reef is situated in a shallow fjord off the Swedish west coast. The number of taxa and their abundance in. transects from the reef itself and from 3 zones (Zone 1 = 50 m, Zone 2 = 100 m and Zone 3 = 200 M) around the reef were compared. Both the number of taxa (from 30 to 33 Tansect(-1)) and the abundance of individuals (from 21 to 7 m(-2)) decreased with increasing distance from the reef. Divided into ecological guilds, predators and filter-feeders decreased with distance from the reef (predators from 7 to 0.3 ind. m(-2), and filter-feeders from 13 to 6 ind. m(-2) from Zone 0 to Zone 3), while deposit-feeders increased with increasing distance from 0.04 to 0.4 ind. m(-2) from Zone 0 to Zone 3. Sessile species decreased more with increasing distance than mobile species, from 19 to 7 ind. m-2 and from 1 to 0.7 ind. m(-2), respectively. Our results also show that small deep-water coral reefs enhance local biodiversity, but the advantage to individual species depends on their mode of feeding and mobility.
In a European effort (Atlantic Coral Ecosystem Study [ACES project]) to determine the key conditions for the occurrence of cold-water corals on the NW Atlantic margin, a coral community on a seamount off NW Spain (Galicia Bank) was studied. Cold-water corals (Lophelia pertusa, Madrepora oculata) grow at a depth of ∼800 m as isolated patches amidst small ripples and larger waves of foraminiferal sand. A 17 mo deployment of a near-bottom sediment trap revealed a large seasonal and annual variability in the flux of phytodetritus and carbon. The daily carbon flux in the first 5 mo of 2000 was on average 37 mgC m -2, and in the first 5 mo of 2001 17 mg C m-2. Quantities of faecal pellets and swimmers (copepods, amphipods) were also highly variable. A comparison between the daily carbon flux and the sediment carbon oxidation rate calculated from in situ community oxygen consumption (SCOC), i.e. 17 versus 7 mg C m-2 d-1 respectively, indicated that a surplus of carbon is not oxidised by the sediment community. We argue that the strong tidal currents (max. 30 cm s-1) and the mobile sediment lead to winnowing of the sediment and to near-bed transport of the organic material. The low biomass of the benthic community and the domination of filter-feeders support our arguments. By means of analyses of stable isotopes (δ15N, δ13C) we attempted to find potential food items of the cold-water corals among the particles collected in the sediment trap. The difference between the δ15N signatures of coral tissue (9.5‰) and phytodetritus (2.2‰) was >1 trophic level, indicating that sinking algae are not the sole food source. The δ15N signatures of swimmers caught in the trap, ∼10‰, were on the other hand in the same range as those of the corals. A mixed diet of animals and algae could be one explanation for the observed δ15N of corals. The δ13C value of the coral tissue, -20.55‰, excludes a food source consisting of bacteria supported by methane seepage, as suggested by earlier studies.
Fishers have been complaining about the effects of bottom trawl gear on the marine environment since at least the 14th century. Trawl gear affects the environment in both direct and indirect ways. Direct effects include scraping and ploughing of the substrate, sediment resuspension, destruction of benthos, and dumping of processing waste. Indirect effects include post‐fishing mortality and long‐term trawl‐induced changes to the benthos. There are few conclusive studies linking trawling to observed environmental changes since it is difficult to isolate the cause. However, permanent faunal changes brought about by trawling have been recorded. Research has established that the degree of environmental perturbation from bottom trawling activities is related to the weight of the gear on the seabed, the towing speed, the nature of the bottom sediments, and the strength of the tides and currents. The greater the frequency of gear impact on an area, the greater the likelihood of permanent change. In deeper water where the fauna is less adapted to changes in sediment regimes and disturbance from storm events, the effects of gear take longer to disappear. Studies indicate that in deep water (>1000 m), the recovery time is probably measured in decades.
The benthic macrofauna of a group of small seamounts south of Tasmania was surveyed
with a dredge and camera to assess the impact of trawling for orange roughy (Hoplostethus atlanticus;
Trachichthyidae) and the efficacy of a proposed marine reserve. The seamounts were generally
300 to 600 m high and the peaks ranged from 660 to 1700 m depth. The fauna was diverse: 262 species
of invertebrates and 37 species of fishes were enumerated, compared with 598 species of invertebrates
previously reported from seamounts worldwide. On seamounts that peaked at depths
<1400 m and that had not been heavily fished, the invertebrate fauna was dense, diverse and dominated
by suspension feeders, including a matrix-forming colonial hard coral (Solenosmilia variabilis)
and a variety of hard and soft (gorgonian and antipatharian) corals, hydroids, sponges and suspension-
feeding ophiuroids and sea stars. Of the invertebrate species, 24 to 43% were new to science,
and between 16 and 33% appeared to be restricted to the seamount environment. Trawl operations
effectively removed the reef aggregate from the most heavily fished seamounts. The benthic biomass
of samples from unfished seamounts was 106% greater than from heavily fished seamounts and the
number of species per sample was 46% greater. Living S. variabilis was not found on seamounts
peaking at depths >1400 m. These seamounts were dominated by sea urchins and had lower biomass
and fewer species per sample. However, few species were restricted to either the shallowest or deepest
depths sampled. The fauna unique to the region’s seamounts appears to be adequately represented
within a recently established ‘Marine Protected Area’ that encloses 12 seamounts that peak at
depths >1150 m.
Scientific report of cruise MSM16/3 of R/V Maria M. Merian devoted to the study of carbonate sedimentation off the Mauritanian coast. The sedimentary system on the shelf and continental slope off Mauritania is of scientific interest for a range of reasons. First, it is one of the rare modern occurrences of eutrophic largescale tropical ecosystems. Nutrient-richt upwelling waters warm up in the shallows of the Golfe d’Arguin and are further fertilized by the influx of Saharan dust. Second, as an effect of the bathymetry of the Golfe d’Arguin, extremely high-resolution sedimentary archives of terrigenous input (eolian and fluviatile) can be interpreted as records of Holocene climatic change. Third, the continental margin off Maurtania is marked by the southernmost known deepwater coral reefs in the eastern North Atlantic. The shelf of Mauritania is climatically and oceanographically exceptionally sensitive and offers the opportunity to put a variety of environmental parameters into a chronologic and causal context. The expedition Maria S. Merian 16-3 aimed at a comprehensive understanding of the complex sedimentary system off Mauritania as an atypical tropical ecosystem and an archive of paleoclimatic change in Africa in the Holocene. The expedition was very successful and exceeded the goals formulated in the original
proposal. During the expedition, the chain of Mauritanian coral reef mounds was mapped the first time and in great detail, revealing a complex and not yet understood large-scale pattern. The zodiac excursions on the shallow Banc d’Arguin in water depth of as little as 2 m led to successful sampling of the carbonate producing organisms, filling an important gap in the understanding of this eutrophic ecosystem. Acoustic profiling with the zodiac revelaled a complex Holocene flooding history of the shallow parts of the Golfe d’Arguin.
Megafauna on bioherms (large biological structures) of the scleractinian coral Lophelia pertusa at 240-290 m depth in the Haltenbanken- Fmyabanken area was investigated by video-recording. Sixteen transects from soft bottom with scattered patches of stones below bioherms to top of bioherms were analysed. Fauna patterns were related to the near-bottom currents. The orientation of the gorgonianParamuricea placomus was used as an indicator of the direction of the main currents at the bioherms. The bioherms were 2 to 31 m high, and had a basal area ranging from 1 500 to 50 600 m2. 36 taxa were identified, of which five taxa only occurred on the bioherms, and five only on the soft bottom with scattered stones. The diversity, H', was highest in the zone of dead Lophelia, and lowest on the silty clay. None of the 26 taxa observed on stones were spesific for this habitat, but occurred also on the bioherms or the soft bottom. The area with Lophelia rubble, near the basis of the bioherms, had the lowest number of taxa (15), but the highest average density of individuals (7.92 ind./1Om2). Different sponges, gorgonians (Paragorgia arborea, Paramuricea placomus, Primnoa resedaeformis), squat lobsters (Munida sarsi), redfish (Sebastes spp.) and saithe (Pollachius virens) dominated in terms of individuals per area. Diversity, density of sponges and density of gorgonians were highest on the down-current side of the bioherms. Saithe were observed with highest densities near the basis of the bioherms, on the up-current side, while redfish had highest densities on the parallel-current side of the bioherm top. These results indicate that near bottom currents and turbulence are factors affecting the fauna on Lophelia bioherms.
The Mingulay reef complex in the Sea of the Hebrides west of Scotland was first mapped in 2003 with a further survey in 2006 revealing previously unknown live coral reef areas at 120 to 190 m depth. Habitat mapping confirmed that distinctive mounded bathymetry was formed by reefs of Lophelia pertusa with surficial coral debris dating to almost 4000 yr. Benthic lander and mooring deployments revealed 2 dominant food supply mechanisms to the reefs: a regular rapid downwelling of surface water delivering pulses of warm fluorescent water, and periodic advection of high turbidity bottom waters. Closed chamber respirometry studies suggest that L. pertusa responds to seawater warming, such as that seen during the rapid downwelling events, with increases in metabolic rate. Lipid biomarker analysis implies that corals at Mingulay feed predominantly on herbivorous calanoid copepods. Integrating geophysical and hydrographical survey data allowed us to quantify the roles of these environmental factors in controlling biodiversity of attached epifaunal species across the reefs. Longitudinal structuring of these communities is striking: species richness (α) and turnover (β) change significantly west to east, with variation in community composition largely explained by bathymetric variables that are spatially structured on the reef complex. Vibro-cores through the reef mounds show abundant coral debris with significant hiatuses. High resolution side-scan sonar revealed trawl marks in areas south of the coral reefs where vessel monitoring system data showed the highest density of local fishing activity. The interdisciplinary approach in this study allowed us to record the food supply and hydrographic environment experienced by L. pertusa and determine how it may be ecophysiologically adapted to these conditions. Improved basic understanding of cold-water coral biology and biodiversity alongside efforts to map and date these long-lived habitats are vital to development of future conservation policies.
Lophelia pertusa is a cold-water coral most frequently reported on the shelf edge and offshore banks of the north east Atlantic. The occurrence of this and other conspicuous large epifauna on moorings 2 km from an oil production platform in the North Sea were recorded from video surveys by remotely operated vehicle. Sea anemones and soft corals were abundant and a total of 133 colonies of L. pertusa were observed. These occurrences and those on the Brent Spar are the first documented reports of live L. pertusa in the North Sea. L. pertusa was restricted in its distribution to water >70 m, below the seasonal thermocline in the northern North Sea. It is estimated that coral sampled from a single point mooring had a linear extension rate of at least 5 mm per year, a rate comparable with existing estimates. It seems likely that these colonies will have originated from populations along the Atlantic margin with larvae transported into the northern North Sea in cooled Atlantic water, possibly via the east Shetland Atlantic Inflow current. The implications of this finding in terms of the environmental sensitivity of this species remain unclear since it is not known to what extent they have been exposed to any drilling discharges. It is possible that corals have persisted on and around oil industry installations as bottom trawling is excluded fram the installation area.
A set of 40 Uranium series datings obtained on the reef-forming scleractinian cold-water corals Lophelia pertusa and Madrepora oculata revealed that during the past 400 kyr their occurrence in the Gulf of Cádiz (GoC) was almost exclusively restricted to glacial periods. This result strengthens the outcomes of former studies that coral growth in the temperate NE Atlantic encompassing the French, Iberian and Moroccan margins dominated during glacial periods, whereas in the higher latitudes (Irish and Norwegian margins) extended coral growth prevailed during interglacial periods. Thus it appears that the biogeographical limits for sustained cold-water coral growth along the NE Atlantic margin are strongly related to climate change. By focussing on the last glacial-interglacial cycle, this study shows that palaeo-productivity was increased during the last glacial. This was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling. After the Younger Dryas cold event, the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the GoC. This primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems. Moreover, these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern NE Atlantic where more suitable environmental conditions established with the onset of the Holocene.
The discovery of mounds and reefs hosting cold‐water coral ecosystems along the northeastern Atlantic continental margins has propelled a vigorous effort over the past decade to study the distribution of the mounds, surface sediments, the ecosystems they host, and their environments [ Hovland et al. , 1994; Freiwald and Roberts , 2005].This effort has involved swath bathymetry, remotely operated vehicle deployments, shallow coring, and seismic surveys.
Global coverage is difficult to gauge, but studies indicate that cold‐water corals may cover as large an area as the better known warm‐water corals that form shallow reefs (284,300 square kilometers) [ Freiwald et al. , 2005]. Cold‐water corals occur in a variety of forms and settings, from small isolated colonies or patch reefs to giant mound structures such as those found west of Ireland.
U-series age patterns obtained on reef framework-forming cold-water corals collected over a nearly 6000-km-long continental margin sector, extending from off Mauritania (17 degrees N; northwest Africa) to the southwestern Barents Sea (70 degrees N; northeastern Europe), reveal strong climate influences on the geographical distribution and sustained development of these ecosystems. Over the past three glacial-interglacial cycles, framework-forming cold-water corals (Lophelia pertusa and Madrepora oculata) seem to have predominantly populated reefs, canyons, and patches in the temperate East Atlantic and the Mediterranean Sea. Above 50 degrees N corals colonize reefs in the northern East Atlantic primarily during warm climate periods with the biogeographic limit advancing from similar to 50 degrees N to similar to 70 degrees N. We propose that north-south oscillations of the biogeographic limit of reef developments are paced by ice ages and may occur synchronously with north-south displacement of cold nutrient-rich intermediate waters and surface productivity related to changes of the polar front.
Bottom trawling is a non-selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor. The direct impact of this technique on fish populations and benthic communities has received much attention, but trawling can also modify the physical properties of seafloor sediments, water–sediment chemical exchanges and sediment fluxes. Most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments, however, where the capacity of trawling to modify the seafloor morphology coexists with high-energy natural processes driving sediment erosion, transport and deposition. Here we show that on upper continental slopes, the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales. We found that trawling-induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time, reducing its original complexity as shown by high-resolution seafloor relief maps. Our results suggest that in recent decades, following the industrialization of fishing fleets, bottom trawling has become an important driver of deep seascape evolution. Given the global dimension of this type of fishery, we anticipate that the morphology of the upper continental slope in many parts of the world’s oceans could be altered by intensive bottom trawling, producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land.
The Mediterranean basin represents an excellent biological archive of past and modern deep coral growth whose study may help
to understand taxonomic, biogeographic, ecological, and evolutionary patterns of modern deep coral bioconstructions, best
embodied by the Lophelia-reefs and mounds of the Atlantic Ocean. In fact, the occurrence of extant deep coral genera in the Mediterranean basin is
documented, although not continuously, since the Miocene. Following the Messinian crisis the re-colonisation of the basin
by deep coral is likely to have started with the Pliocene but little is known about deep coral biota linked to hard substrates
during this epoch. It is certain that Atlantic-type deep-sea corals including the scleractinian triad Lophelia-Madrepora-Desmophyllum have been established in the basin since the latest Pliocene-Early Pleistocene as proven by outcrop evidence in southern
Italy, especially Sicily and Calabria, and in Rhodes. Still-submerged dead coral assemblages are widespread in the entire
basin between c. 250—2500 m depth; the majority is aged at the last glacial by AMS, C14 and U/Th dating. The present situation
(post-glacial) is a general decline of such deep corals in the Mediterranean, and this is especially true for Lophelia which appears to be more severely affected by local extinctions. To date, the only exception to this general rule is represented
by the recent discovery of prosperous Lophelia populations in the Eastern Ionian Sea.
Cold-water coral carbonate mounds, owing their presence mainly to the framework building coral Lophelia pertusa and the activity of associated organisms, are common along the European margin with their spatial distribution allowing them to be divided into a number of mound provinces. Variation in mound attributes are explored via a series of case studies on mound provinces that have been the most intensely investigated: Belgica, Hovland, Pelagia, Logachev and Norwegian Mounds. Morphological variation between mound provinces is discussed under the premise that mound morphology is an expression of the environmental conditions under which mounds are initiated and grow. Cold-water coral carbonate mounds can be divided into those exhibiting “inherited” morphologies (where mound morphology reflects the morphology of the colonised features) and “developed” morphology (where the mounds assume their own gross morphology mainly reflecting dominant hydrodynamic controls). Finer-scale, surface morphological features mainly reflecting biological growth forms are also discussed.
Twenty five blocks of Lophelia pertusa weighing a total of 18.5 kg were studied. Associated with this substrate were 4 626 individuals belonging to 256 species. An additional 42 species were identified from loose coral rubble. Of the 298 species found, 97 are recorded for the first time from the area around the Faroes. Most individuals were found in dead coral blocks from the inner parts of the bank or colony, but a few species were found close to the terminal branches of live coral blocks. The associated fauna of this branching deep-water coral was as rich and diverse as that of hermatypic branching species of coral. Some physical features of the coral as a substrate were measured. Large blocks of live coral harbour a more diverse fauna than do smaller ones. In contrast, on dead coral blocks the number of species and individuals had no simple correlation to block size, indicating the importance of other factors such as random colonization and length of time the substrate has been inhabited. Of the 20 most abundant species only four showed a correlation between the number of individuals and coral weight. Ecological aspects of the associated fauna are discussed and the results are compared with studies from associations on hermatypic corals. Comparing with studies of Lophelia banks from Norway and the Bay of Biscay we find very few overlaps in the associated species. A highly diverse and rich but facultative fauna is associated with the Lophelia banks.
Coral reefs are something we usually associate with warm, tropical waters and exotic fish, but not with the cold, deep and dark waters of the North Atlantic, where corals were regarded as oddities on the seafloor. It is now known that cold-water coral species also produce reefs which rival their tropical cousins in terms of their species richness and diversity. Increasing commercial operations in deep waters, and the use of advanced offshore technology have slowly revealed the true extent of Europe’s hidden coral ecosystems. This article reviews current knowledge about the reef-forming potential and the environmental controls of the scleractinian Lophelia pertusa along different deep-shelf and continental margin settings with special reference to NE Atlantic occurrences.
IODP Expedition 307 made it for the first time possible to investigate the entire body of a cold-water coral carbonate mound. Here we provide new insights into the long-term history of Challenger Mound on the European continental margin off Ireland. This study is based on age determinations (230Th/U, 87Sr/86Sr) and geochemical signals (Mg/Li and Ba/Ca) measured in the scleractinian cold-water coral Lophelia pertusa from IODP Site 1317 in the Porcupine Seabight. The paleoceanographic reconstructions reveal that coral growth in the Porcupine Seabight was restricted to specific oceanographic conditions such as enhanced export of primary production and Bottom-Water Temperatures (BWT) between ∼8 and 10 °C, related to the water mass stratification of the Mediterranean Outflow Water (MOW) and Eastern North Atlantic Water (ENAW). The geochemical signals from the coral skeletons can be explained by the close interaction between cold-water coral growth, sea-surface productivity and the surrounding water masses – the boundary layer between MOW and ENAW. Enhanced sea-surface productivity and the build-up of a stable water mass stratification between ENAW and MOW caused enhanced nutrient supply at intermediate water depths and facilitated a steady mound growth between ∼3.0 and 2.1 Ma. With the decrease in sea-surface productivity and related reduced export productivity the food supply was insufficient for rapid coral mound growth between ∼1.7 and 1 Ma. During the late Pleistocene (over the last ∼0.5 Myr) mound growth was restricted to interglacial periods. During glacials the water mass boundary between ENAW/MOW probably was below the mound summit and hence food supply was not sufficient for corals to grow.
Along the Atlantic European continental margin, living cold-water coral reefs occur over a wide bathymetric and hydrographical range. Focusing on 2 regions, the Celtic and the Norwegian shelves, we found that cold-water coral reefs are limited to different intermediate water masses. Measurements of the physical and geological properties showed that parameters such as temperature, salinity, dissolved oxygen content, current intensities, and different substrates vary widely without specifically impacting the distribution of living cold-water coral reefs. The habitat of living reefs within the NE Atlantic comprises a temperature-salinity field, with its lower boundary equivalent to the Intermediate Salinity Maximum (ISM). The ISM on the Celtic margin is represented by Mediterranean Outflow Water (MOW), but is replaced by Atlantic Water (AW) on the Norwegian margin. The upper limit corresponds to water mass boundaries of Eastern North Atlantic Water/MOW on the Celtic margin and Norwegian Coastal Water/AW on the Norwegian margin. Our study shows that cold-water corals in the North Atlantic tolerate a wide range of environmental conditions. However, our data indicate that living cold-water coral reefs occur within the density envelope of sigma-theta (sigma(Theta)) = 27.35 to 27.65 kg m(-3), thus highlighting the importance of physical boundary conditions for cold-water coral growth and distribution.
The cold-water scleractinian corals Lophelia pertusa and Madrepora oculata form mound structures on the continental shelf and slope in the NE Atlantic. This study is the first to compare the taxonomic biodiversity and ecological composition of the macrobenthos between on- and off-mound habitats. Seven box cores from the summits of three mounds and four cores from an adjacent off-mound area in the Belgica Mound Province in the Porcupine Seabight yielded 349 species, including 10 undescribed species. On-mound habitat was three times more speciose, and was richer with higher evenness and significantly greater Shannon's diversity than off-mound. Species composition differed significantly between habitats and the four best discriminating species were Pliobothrus symmetricus (more frequent off-mound), Crisia nov. sp, Aphrocallistes bocagei and Lophelia pertusa (all more frequent on-mound). Filter/suspension feeders were significantly more abundant on-mound, while deposit feeders were significantly more abundant off-mound. Species composition did not significantly differ between mounds, but similarity within replicates decreased from Galway Mound
In 2006 and 2007, multiple deployments of current meters and optical sensors on landers and moorings were made in the first detailed in situ study of the particle supply to the coral community in the Mingulay Reef complex in the Sea of Hebrides at 140-m water depth. Two distinct and predictable supply mechanisms were resolved. One mechanism consisted of the rapid downwelling of surface water caused by hydraulic control of tidal flow that transports particles from the surface to the corals in less than an hour. The rapid downwelling was recorded on the reef top as a pulse of warm, fluorescent, and relatively clear water at the onset of the flood and ebb tides. The pulse was strongest after flood tide and lasted for up to 3 h. The second mechanism consisted of advection onto the reef of deep bottom water with a high suspended matter load. This advection occurred during peak tides and was combined with topographical current acceleration on the reef top, enhancing delivery of particles to the corals.
Expeditions from 1999 to 2004 for biomedical research explored various deep-sea coral ecosystems (dSCE) off the southeastern U.S. (Blake Plateau, Straits of Florida, and eastern Gulf of Mexico). Habitat and benthos were documented from 57 dives with human occupied submersibles and three with a remotely operated vehicle (ROV), and resulted in ∼100 hrs of videotapes, 259 in situ digital images, 621 museum specimens, and > 400 microbial isolates. These were the first dives to document the habitat, benthic fauna, and fish diversity of some of these poorly known deep-water reefs. Fifty-eight fish species and 142 benthic invertebrate taxa were identified. High-definition topographic SEABEAM maps and echosounder profiles were also produced. Sites included in this report range from South Carolina on the Blake Plateau to the southwestern Florida slope: 1) Stetson Lophelia reefs along the eastern Blake Plateau off South Carolina; 2) Savannah Lophelia lithoherms along the western Blake Plateau off Georgia; 3) east Florida Lophelia reefs, 4) Miami Terrace escarpment in the Straits of Florida; 5) Pourtalès Terrace off the Florida keys; and 6) west Florida Lophelia lithoherms off the southwestern Florida shelf in the Gulf of Mexico. These are contrasted with the azooxanthellate deep-water oculina reefs at the shelf-edge off central eastern Florida. The fisheries and biopharmaceutical resource potential of these deep-water habitats remain relatively unknown. Although these habitats are not currently designated as marine protected areas (MPAs) or coral habitat areas of particular concern (HAPCs), they are ecologically diverse, vulnerable to physical destruction, and irreplaceable resources. Activities involving bottom trawling, pipelines, or oil/gas production could negatively impact these reefs. National Oceanic and Atmospheric Administration (NOAA) Fisheries and the South Atlantic Fishery Management Council are currently developing priority mapping sites of the dSCEs within this region, and these data may provide potential targets for new MPAs and HAPCs.
Deep‐water corals are widely distributed along the cold‐temperate northeastern Atlantic continental margin. Despite the widespread occurrence of these aphotic coral constructions in deep shelf settings, the processes of framework formation and postmortem alterations which result in different preservational styles are still poorly known. Detailed mapping surveys on probably one of the largest Lophelia reef structures were carried out on the Sula Ridge, Mid‐Norwegian Shelf in 270 to 300 m depth. Side scan sonar records and camera surveys yield information at various scales of resolution on the reef complex which is more than 9 km long and up to 45 m high. Living Lophelia colonies effectively prevent colonization by other organisms and are successful in the rejection of passing detrital material from the soft tissue. In a healthy condition the coral is able to encrust repetitively attached organisms by selectively secreted sclerenchyme layers, thus, this defensive reaction results in the thickening of the skeleton. Early postmortem alteration in Lophelia colonies is introduced by the formation of a biofilm and Dodgella (fungi) infestation. The biofilm is associated with selective Fe‐Mn precipitation on the coral skeleton. This is the zone of intense attachment of sessile invertebrates such as serpulids, brachiopods, foraminifers and encrusting bryozoans. More advanced taphonomic stages show an increasing dominance in sponges which reduce the interskeletal framework porosity significantly. In addition, boring sponges excavate the thickly calcified Lophelia skeletons, thus leading to in situ collapsing structures on the sea floor. It is the intensity of sediment trapping biofilms and sponge colonization and the amount of imported detrital particles predominantly from the pelagial zone that control the generation of a pure coral rubble facies or the preservation of collapsed but mud‐rich detrital mounds.
Continuous sedimentary records from an eastern Mediterranean cold-water coral ecosystem thriving in intermediate water depths ($ 600 m) reveal a temporary extinction of cold-water corals during the Early to Mid Holocene from 11.4–5.9 cal kyr BP. Benthic foraminiferal assemblage analysis shows low-oxygen conditions of 2 ml l À 1 during the same period, compared to bottom-water oxygen values of 4–5 ml l À 1 before and after the coral-free interval. The timing of the corals' demise coincides with the sapropel S1 event, during which the deep eastern Mediterranean basin turned anoxic. Our results show that during the sapropel S1 event low oxygen conditions extended to the rather shallow depths of our study site in the Ionian Sea and caused the cold-water corals temporary extinction. This first evidence for the sensitivity of cold-water corals to low oceanic oxygen contents suggests that the projected expansion of tropical oxygen minimum zones resulting from global change will threaten cold-water coral ecosystems in low latitudes in the same way that ocean acidification will do in the higher latitudes.
This paper presents the first compilation of information on the spatial distribution of scleractinian cold-water corals in the Gulf of Cádiz based on literature research and own observations (video footage, sediment samples). Scleractinian cold-water corals are widely distributed along the Spanish and Moroccan margins in the Gulf of Cádiz, where they are mainly associated with mud volcanoes, diapiric ridges, steep fault escarpments, and coral mounds. Dendrophyllia cornigera, Dendrophyllia alternata, Eguchipsammia cornucopia, Madrepora oculata and Lophelia pertusa are the most abundant reef-forming species. Today, they are almost solely present as isolated patches of fossil coral and coral rubble. The absence of living scleractinian corals is likely related to a reduced food supply caused by low productivity and diminished tidal effects. In contrast, during the past 48 kyr scleractinian corals were abundant in the Gulf of Cádiz, although their occurrence demonstrates no relationship with main climatic or oceanographic changes. Nevertheless, there exists a conspicuous relationship when the main species are considered separately. Dendrophylliids are associated with periods of relatively stable and warm conditions. The occurrence of L. pertusa mainly clusters within the last glacial when bottom current strength in the Gulf of Cádiz was enhanced and long-term stable conditions existed in terms of temperature. Madrepora oculata shows a higher tolerance to abrupt environmental changes.
a b s t r a c t This paper presents the first compilation of information on the spatial distribution of scleractinian cold-water corals in the Gulf of Cá diz based on literature research and own observations (video footage, sediment samples). Scleractinian cold-water corals are widely distributed along the Spanish and Moroccan margins in the Gulf of Cá diz, where they are mainly associated with mud volcanoes, diapiric ridges, steep fault escarpments, and coral mounds. Dendrophyllia cornigera, Dendrophyllia alternata, Eguchipsammia cornucopia, Madrepora oculata and Lophelia pertusa are the most abundant reef-forming species. Today, they are almost solely present as isolated patches of fossil coral and coral rubble. The absence of living scleractinian corals is likely related to a reduced food supply caused by low productivity and diminished tidal effects. In contrast, during the past 48 kyr scleractinian corals were abundant in the Gulf of Cá diz, although their occurrence demonstrates no relationship with main climatic or oceanographic changes. Nevertheless, there exists a conspicuous relationship when the main species are considered separately. Dendrophylliids are associated with periods of relatively stable and warm conditions. The occurrence of L. pertusa mainly clusters within the last glacial when bottom current strength in the Gulf of Cá diz was enhanced and long-term stable conditions existed in terms of temperature. Madrepora oculata shows a higher tolerance to abrupt environmental changes.
A set of 40 Uranium-series datings obtained on the reef-forming scleractinian cold-water corals Lophelia pertusa and Madrepora oculata revealed that during the past 400 kyr their occurrence in the Gulf of Cádiz (GoC) was almost exclusively restricted to glacial periods. This result strengthens the outcomes of former studies that coral growth in the temperate NE Atlantic encompassing the French, Iberian and Moroccan margins dominated during glacial periods, whereas in the higher latitudes (Irish and Norwegian margins) extended coral growth prevailed during interglacial periods. Thus it appears that the biogeographical limits for sustained cold-water coral growth along the NE Atlantic margin are strongly related to climate change. By focussing on the last glacial–interglacial cycle, this study shows that palaeo-productivity was increased during the last glacial. This was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling. After the Younger Dryas cold event, the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the GoC. This primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems. Moreover, these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern NE Atlantic where more suitable environmental conditions established with the onset of the Holocene.
Cold-water corals are widely distributed along the Atlantic continental margin with varying growth patterns in relation to their specific environment. Here, we investigate the long-term development of cold-water corals that once thrived on a low-latitude (17°40′N) cold-water coral mound in the Banda Mound Province off Mauritania during the last glacial–interglacial cycle. U/Th dates obtained from 20 specimens of the cold-water coral Lophelia pertusa, revealed three distinct periods of coral growth during the last glacial at 65 to 57 kyr BP, 45 to 32 kyr BP and 14 kyr BP, thus comprising the cool periods of Marine Isotopic Stages (MIS) 2–4. These coral growth periods occur during periods of increased productivity in the region, emphasizing that productivity seems to be the major steering factor for coral growth off Mauritania, which is one of the major upwelling regions in the world. This pattern differs from the well studied coral mounds off Ireland, where the current regime predominantly influences the prosperity of the cold-water corals. Moreover, coral growth off Ireland takes place during rather warm interglacial and interstadial periods, whereas off Mauritania coral growth is restricted to glacial and stadial periods. However, the on-mound sedimentation patterns off Mauritania largely resemble the observations reported from the Irish mounds. The bulk of the preserved sediments derives from periods of coral growth, whereas during periods without corals hardly any net sedimentation or mound growth took place.
The answer to the title question is uncertain, as very few manipulative experiments have been conducted to test how deep-sea scleractinians (stony corals) react to changes in seawater chemistry. Ocean pH and calcium carbonate saturation are decreasing due to an influx of anthropogenic CO2 to the atmosphere. Experimental evidence has shown that declining carbonate saturation inhibits the ability of marine organisms to build calcium carbonate skeletons, shells, and tests. Here we put forward a hypothesis suggesting that the global distribution of deep-sea scleractinian corals could be limited in part by the depth of the aragonite saturation horizon (ASH) in the world's oceans. Aragonite is the metastable form of calcium carbonate used by scleractinian corals to build their skeletons and the ASH is the limit between saturated and undersaturated water. The hypothesis is tested by reviewing the distribution of deep-sea, bioherm-forming scleractinian corals with respect to the depth of the ASH. Results indicate that > 95% of 410 coral locations occurred in saturated waters during pre-industrial times. Projections indicate that about 70% of these locations will be in undersaturated waters by 2099. Lab experimentation, in situ experimentation, and monitoring efforts are needed to quantify the effects of changing seawater chemistry on deep-sea coral ecosystems.
The first detailed stratigraphic record from a deep-water carbonate mound in the Northeast Atlantic based on absolute datings (U/Th and AMS 14 C) and stable oxygen isotope records reveals that its top sediment sequences are condensed by numerous hiatuses. According to stable isotope data, mainly sediments with an intermediate signal are preserved on the mound, while almost all fully glacial and interglacial sediments have either not been deposited or have been eroded later. The resulting hiatuses reduce the Late Pleistocene sediment accumulation at Propeller Mound to amounts smaller than the background sedimentation. The hiatuses most likely result due to the sweeping of the mound in turn with the re-establishment of vigour interglacial circulation patterns after sluggish current regimes during glacials. Thus, within the discussion if internal, fluid-driven or external environmentally driven processes control the evolution of such carbonate mounds, our findings for Propeller Mound clearly 0012-821X/$ -see front matter D 2005 Elsevier B.V. All rights reserved.
Nine new intermediate water ages estimated with coupled uranium-series and radiocarbon measurements on deep-sea corals from the northeastern Atlantic are presented. Together with six intermediate and deep-water ages from the western North Atlantic [Adkins et al., Science 280 (1998) 725–728] and one from the equatorial Atlantic [Mangini et al., Nature 392 (1998) 347–348] they span the time period from 15 400 to 560 yr ago and show abrupt variations of intermediate and deep-water ages from 270 up to 2320 yr. Both major pulses of meltwater discharge MWP 1A, following Heinrich Event 1 and MWP 1B after the Younger Dryas cold event are followed by enhanced supply of southern source water at intermediate depths in the North Atlantic, together with reduced formation of well-ventilated glacial North Atlantic intermediate water (1000–2000 m). This result gives strong support to numerical models, predicting fast and sharp increase of bottom water age in the Atlantic triggered by pulses of freshwater discharge into the North Atlantic [Rahmstorf, Nature 372 (1994) 82–85; Stocker and Wright, Radiocarbon 40 (1998) 359–366].
This report was compiled at the request of the South Atlantic Fishery Management Council (SAFMC) to provide a preliminary, general summary on the status of current knowledge concerning deep-water (> 200 m) reefs off the southeastern U.S. from Florida to North Carolina. The outcome will provide target areas of deep-water, live-bottom habitats for: 1) potential designation as Habitat Areas of Particular Concern (HAPC) or Marine Protected Areas (MPA) by the SAFMC, and 2) high-resolution habitat maps and habitat characterization studies. The resource potential of the deep-water habitats in this region is unknown in terms of fisheries and novel compounds yet to be discovered from associated fauna that may be developed as pharmaceutical drugs. Although these habitats have not been designated as MPAs or HAPCs, they are incredibly diverse and irreplaceable resources. Activities involving bottom trawling, pipelines, or oil/gas production could negatively impact these reefs. This report primarily summarizes recent submersible data regarding deep-water reefs off Florida but also includes sites off Georgia and South Carolina. A report on the North Carolina reefs has been submitted separately by Dr. Steve Ross, UNCW. This report does not include the deep-water Oculina reefs off central eastern Florida or deep shelf-edge reefs with hermatypic coral (<100 m). The sites included in this report are the following: 1) Stetson Reefs-hundreds of pinnacles along the eastern Blake Plateau off South Carolina include a 152-m tall pinnacle (822 m depth) where recent submerisible dives discovered live bushes of Lophelia coral, sponges, gorgonians, and black coral bushes. 2) Savannah Lithoherms-numerous lithoherms at depths of 550 m with relief up to 60 m provide live-bottom habitat. 3) East Florida Lophelia Reefs-echosounder transects along a 222-km stretch off eastern Florida (depth 700-800 m) mapped hundreds of 15-152 m tall coral pinnacles and lithoherms. 4,5) Miami Terrace and Pourtales Terrace-Miocene age terraces off southeastern Florida and the Florida reef tract provide high-relief, hard-bottom habitats and rich benthic communites. 6) SW Florida Lithoherms-in the Gulf of Mexico off the southwestern Florida shelf slope, 15-m tall Lophelia coral lithoherms (500 m depth) are described the first time from SEABEAM and ROV dives.
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.
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.