Cold-water coral habitats in the Penmarc'h and Guilvinec Canyons (Bay of Biscay): Deep-water versus shallow-water settings

Abstract

In 1948, Le Danois reported for the first time the occurrence of living cold-water coral reefs, the socalled "massifs coralliens", along the European Atlantic continental margin. In 2008, a cruise with R/V Belgica was set out to re-investigate these cold-water corals in the Penmarc'h and Guilvinec Canyons along the Gascogne margin of the Bay of Biscay. During this cruise, an area of 560 km2 was studied using multibeam swath bathymetry, CTD casts, ROV observations and USBL-guided boxcoring.Based on the multibeam data and the ROV video imagery, two different cold-water coral reef settings were distinguished. In water depths ranging from 260 to 350 m, mini mounds up to 5 m high, covered by dead cold-water coral rubble, were observed. In between these mounds, soft sediment with a patchy distribution of gravel was recognised. The second setting (350-950 m) features hard substrates with cracks, spurs, cliffs and overhangs. In water depths of 700 to 950 m, both living and dead cold-water corals occur. Occasionally, they form dense coral patches with a diameter of about 10-60 m, characterised by mostly stacked dead coral rubble and a few living specimens. U/Th datings indicate a shift in cold-water coral growth after the Late Glacial Maximum (about 11.5 ka BP) from shallow to deep-water settings.The living cold-water corals from the deeper area occur in a water density (sigma-theta) of 27.35-27.55 kg m− 3, suggested to be a prerequisite for the growth and distribution of cold-water coral reefs along the northern Atlantic margin. In contrast, the dead cold-water coral fragments in the shallow area occur in a density range of 27.15-27.20 kg m− 3 which is slightly outside the density range where living cold-water corals normally occur. The presented data suggest that this prerequisite is also valid for coral growth in the deeper canyons (> 350 m) in the Bay of Biscay.

Distribution of cold-water corals in the Whittard Canyon, NE Atlantic Ocean

“…The Aragonite Saturation Horizon (ASH) may limit the distribution of Lophelia (Turley et al, 2007). It occurs at a depth of about 2000 m within the Bay of Biscay (de Mol et al, 2011: Davies et al, 2008. Therefore the lower distribution limit of Lophelia in the Whittard Canyon (2448 m) may be associated with the Aragonite Saturation Horizon.…”

“…A steep pycnocline separates the ENACW from Mediterranean Outflow Water (MOW). The MOW extends down to about 1200 m, mixing with the underlying Labrador Sea Water marked by a salinity minimum at around 1800 m. There is some influence of Norwegian Sea Water at around 2000 m. Below this depth North Atlantic Deep Water (NADW) derived from Greenland appears, and is heavily influenced by the pervading Atlantic Antarctic Bottom Water at greater depths (Matthias and Godfrey, 2003;Aminot and Kerouel, 2004;De Mol et al, 2011).…”

Cold-Water Coral Habitats in Submarine Canyons of the Bay of Biscay

“…Mapping and understanding the distribution of CWC habitats is, therefore, needed for conservation management along European margins. As a result of the importance of this part of the NE Atlantic as an integral sector or transition zone of this margin (Reveillaud et al, 2008;De Mol et al, 2011), the Bay of Biscay could potentially play a large role in persistence of those ecosystems on a global scale and, thus, potentially important for the connectivity between regions.…”

“…However, the first maps of scleractinian occurrences were produced in the following century: Joubin (1922) used fishermen reports on scleractinians causing damage to demersal trawls and Le Danois (1948) mapped coral reefs along the continental slope of the Bay. Despite this early discovery, only a few CWC studies had been undertaken in the French part of the Bay of Biscay (Zibrowius, 1980;Reveillaud et al, 2008;De Mol et al, 2011) and the largest part of this basin still remains unexplored.…”

Carbonate mounds: From paradox to World Heritage

“…The remarkable resolution achieved in seismic imaging, multibeam bathymetry and habitat mapping in Porcupine Seabight, in the Bay of Biscay and on the Moroccan North-Atlantic margin in water depths ranging between 300 and 1300 m has shed light on vast fields of small cold-water coral capped hummocks, barely a few meters in amplitude (Masson et al, 2003;Wheeler et al, 2008;Huvenne et al, 2009;De Mol et al, 2011;Foubert et al, 2011;Wheeler et al, 2011), or coralcapped giant ripples, up to 10 to 20 m in amplitude (Mienis, 2007;Correa et al, 2012). In the early days of modern mound exploration on the Irish margin, the frequent spatial association of such fields of coral-capped hummocks and giant cold-water coral mounds fuelled the hypothesis that those small mounded features possibly could represent the embryonic stage of giant mounds, and still recently, contrasting views persist on this matter (Wilson et al, 2007;Foubert et al, 2011;Wheeler et al, 2011).…”