Copyright : Laboratoire LEMAR- 2018
Hammoud EL VADHEL
Lénaick MENOT et Lene Buhl-Mortensen
IMROP
The cold-water coral (CWC) reefs are found in all oceans and seas around the world. They occur mainly along the continental margins. Although known since Antiquity, corals in deep, cold waters remained largely unappreciated and overlooked by the scientific community until the 1990s (Roberts and Cairns 2014). The observation and study of cold-water coral habitats in their natural surroundings began in the last 20 years when scientists and the industry started to use increasingly sophisticated underwater instrumentation (e.g. ROVs …) to map.
Cold-water coral ecosystems occur mainly on continental margins and in the Atlantic, corals occur from Northern Norway and Iceland (Buhl-Mortensen et al. 2019) to central Africa (Buhl-Mortensen et al. 2017, Weinberg et al. 2018). In some regions off west Africa corals have been associated with complicated seabed structures several hundred meters high (Weinberg et al. 2018, Hebbeln et al. 2019).
Like their shallow tropical counterparts, cold-water corals engineer habitats that support many other species. A European margin census in 2003 listed over 1300 species recorded with Lophelia pertusa habitats in the NE Atlantic (Roberts JM et al, 2006).
The cold-water coral reefs are global biodiversity and biogeochemical cycling hotspots and play host to thousands of animal species throughout the ocean food web. CWC reefs not only enhance species diversity and harbor distinct assemblages across the reef structure but these ecosystems also enhance regional and global diversity (Buhl-Mortensen et al. 2010, Henry, L. A., & Roberts, J. M., 2017). Just in recent years, a hydrocarbon offshore exploration of the Mauritanian continental margin discovered a large linear structure of carbonate mounds over at least 190 km (Colman et al. 2005). Subsequently, scientific surveys were carried out in the deep sea off Mauritania aboard several research vessels, German (R/V Poseidon and R/V Maria S. Merian), Spanish (R/V Vizconde de Eza) and Norwegian (R/V Fridtjof Nansen) to collect data on deep habitats in Mauritania. Few studies have been carried out on cold-water coral off Mauritania. Colman et al. (2005) was the first who described the Mauritanian coral mounds, and then other authors studied the CWC of Mauritania (Krastel, S et al., 2006; M. Eisele et al., 2011; Ramos et al., 2017; Weinberg et al., 2018).
The largest coherent cold-water coral (CWC) mound province in the Atlantic Ocean exists along the Mauritanian margin, where up to 100 m high mounds extend over a distance of ~400 km, arranged in two slope-parallel chains in 400-550 m water depth (Hebbeln et al. 2019, Weinberg et al, 2018). The Mauritanian zone is recognized as being a region of very high biological productivity, this productivity, which is mainly favored by the upwelling of the Canaries, results in a significant abundance of fishery resources. In this region, the fishery resources have been exploited for centuries.
The Mauritania waters support one of the oldest and most important West African fisheries (Khallahi B et al, 2020). The deep-sea fishing is practiced by different national and foreign fleets, which comprise demersal and pelagic fishing vessels trawling in the vulnerable marine ecosystems such as cold-water coral. In recent years, Mauritanian waters have become a destination for many offshore gas exploration and exploitation companies (Exxon Mobil, Shell, BP, Total, Kosmos Energy, Tullow Oil, Petronas…) The discovery of the Greater Tortue Ahemyim (GTA) located on the maritime border between Mauritania and Senegal at a depth of 2,850m is considered to be the largest ever carried out on the West African coast. The first gas expected to be produced in 2023 by BP with a 30-50-year production potential. Although we are starting to realize the ubiquity of cold-water coral reefs, their biodiversity and value as habitat for many commercial species and human activities are still a threat to these ecosystems. Some main threats are bottom trawling causing damage, (ii) hydrocarbon drilling and seabed mining increasing risk of silting/ smothering, and (iii) climate change with increased temperature and hypoxia.
In this context, this PhD-project will study the cold-water coral reefs on the continental margin off Mauritania with focus on their distribution, ecosystem characterization and the anthropogenic impact using video observation from the habitat surveys carried out in 2020 and 2021 in Mauritanian waters by the R/V Dr. Fridtjof Nansen. In addition, the coral habitat description will benefit from oceanography data (e.g. temperature, dissolved oxygen, and nutrients) and sea floor bathymetric from Multibeam echo sounder achieved on these surveys.
The cold-water coral (CWC) reefs are found in all oceans and seas around the world. They occur mainly along the continental margins. Although known since Antiquity, corals in deep, cold waters remained largely unappreciated and overlooked by the scientific community until the 1990s (Roberts and Cairns 2014). The observation and study of cold-water coral habitats in their natural surroundings began in the last 20 years when scientists and the industry started to use increasingly sophisticated underwater instrumentation (e.g. ROVs …) to map.
Cold-water coral ecosystems occur mainly on continental margins and in the Atlantic, corals occur from Northern Norway and Iceland (Buhl-Mortensen et al. 2019) to central Africa (Buhl-Mortensen et al. 2017, Weinberg et al. 2018). In some regions off west Africa corals have been associated with complicated seabed structures several hundred meters high (Weinberg et al. 2018, Hebbeln et al. 2019).
Like their shallow tropical counterparts, cold-water corals engineer habitats that support many other species. A European margin census in 2003 listed over 1300 species recorded with Lophelia pertusa habitats in the NE Atlantic (Roberts JM et al, 2006).
The cold-water coral reefs are global biodiversity and biogeochemical cycling hotspots and play host to thousands of animal species throughout the ocean food web. CWC reefs not only enhance species diversity and harbor distinct assemblages across the reef structure but these ecosystems also enhance regional and global diversity (Buhl-Mortensen et al. 2010, Henry, L. A., & Roberts, J. M., 2017). Just in recent years, a hydrocarbon offshore exploration of the Mauritanian continental margin discovered a large linear structure of carbonate mounds over at least 190 km (Colman et al. 2005). Subsequently, scientific surveys were carried out in the deep sea off Mauritania aboard several research vessels, German (R/V Poseidon and R/V Maria S. Merian), Spanish (R/V Vizconde de Eza) and Norwegian (R/V Fridtjof Nansen) to collect data on deep habitats in Mauritania. Few studies have been carried out on cold-water coral off Mauritania. Colman et al. (2005) was the first who described the Mauritanian coral mounds, and then other authors studied the CWC of Mauritania (Krastel, S et al., 2006; M. Eisele et al., 2011; Ramos et al., 2017; Weinberg et al., 2018).
The largest coherent cold-water coral (CWC) mound province in the Atlantic Ocean exists along the Mauritanian margin, where up to 100 m high mounds extend over a distance of ~400 km, arranged in two slope-parallel chains in 400-550 m water depth (Hebbeln et al. 2019, Weinberg et al, 2018). The Mauritanian zone is recognized as being a region of very high biological productivity, this productivity, which is mainly favored by the upwelling of the Canaries, results in a significant abundance of fishery resources. In this region, the fishery resources have been exploited for centuries.
The Mauritania waters support one of the oldest and most important West African fisheries (Khallahi B et al, 2020). The deep-sea fishing is practiced by different national and foreign fleets, which comprise demersal and pelagic fishing vessels trawling in the vulnerable marine ecosystems such as cold-water coral. In recent years, Mauritanian waters have become a destination for many offshore gas exploration and exploitation companies (Exxon Mobil, Shell, BP, Total, Kosmos Energy, Tullow Oil, Petronas…) The discovery of the Greater Tortue Ahemyim (GTA) located on the maritime border between Mauritania and Senegal at a depth of 2,850m is considered to be the largest ever carried out on the West African coast. The first gas expected to be produced in 2023 by BP with a 30-50-year production potential. Although we are starting to realize the ubiquity of cold-water coral reefs, their biodiversity and value as habitat for many commercial species and human activities are still a threat to these ecosystems. Some main threats are bottom trawling causing damage, (ii) hydrocarbon drilling and seabed mining increasing risk of silting/ smothering, and (iii) climate change with increased temperature and hypoxia.
In this context, this PhD-project will study the cold-water coral reefs on the continental margin off Mauritania with focus on their distribution, ecosystem characterization and the anthropogenic impact using video observation from the habitat surveys carried out in 2020 and 2021 in Mauritanian waters by the R/V Dr. Fridtjof Nansen. In addition, the coral habitat description will benefit from oceanography data (e.g. temperature, dissolved oxygen, and nutrients) and sea floor bathymetric from Multibeam echo sounder achieved on these surveys.
The aim of this study is to map CWC habitat from Cap Blanc to the border with Senegal, to determine their distribution, the associated biodiversity, and the environmental factors that control their distribution in the area and the main threats they face in order to manage this vulnerable ecosystem. The habitat of Mauritanian reefs will be compared with other reef settings both off Africa and in the reef rich area off Norway. More specifically, this thesis aims to:
- Achieve a complete mapping of the distribution of cold-water coral off Mauritania, and to develop high-resolution maps for areas where corals are known to exist from the northern area (Cap Blanc) to the southern border with area Senegal.
- Describe and characterize the CWC ecosystem and the associated diversity.
- Compare the habitat of CWC in Mauritanian waters with other coral habitation the hypoxic upwelling zone off Africa with North Atlantic reefs (Norway) in well oxygenated waters.
- Propose development measures for this vulnerable habitat in order to illuminate the various threats (Trawling, hydrocarbon exploration …).
The aim of this study is to map CWC habitat from Cap Blanc to the border with Senegal, to determine their distribution, the associated biodiversity, and the environmental factors that control their distribution in the area and the main threats they face in order to manage this vulnerable ecosystem. The habitat of Mauritanian reefs will be compared with other reef settings both off Africa and in the reef rich area off Norway. More specifically, this thesis aims to:
- Achieve a complete mapping of the distribution of cold-water coral off Mauritania, and to develop high-resolution maps for areas where corals are known to exist from the northern area (Cap Blanc) to the southern border with area Senegal.
- Describe and characterize the CWC ecosystem and the associated diversity.
- Compare the habitat of CWC in Mauritanian waters with other coral habitation the hypoxic upwelling zone off Africa with North Atlantic reefs (Norway) in well oxygenated waters.
- Propose development measures for this vulnerable habitat in order to illuminate the various threats (Trawling, hydrocarbon exploration …).
2026
Discovery
