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

Abstract

The topographical and hydrological complexity of submarine canyons, coupled with high substratum heterogeneity, make them ideal environments for cold-water coral (CWC) habitats. These habitats, including reefs, are thought to provide important functions for many organisms. The canyons incising the continental slope of the Bay of Biscay have distinct morphological differences from the north to the south. CWCs have been reported from this basin in the late nineteenth century; however, little is known about their present-day distribution, diversity and environmental drivers in the canyons. In this study, the characteristics and distribution of CWC habitats in the submarine canyons of the Bay of Biscay are investigated. Twenty-four canyons and three locations between adjacent canyons were sampled using a Remotely Operated Vehicle (ROV) or a towed camera system. Acquired images were annotated for habitat type (using the CoralFISH classification system), substrate cover and coral identification. Furthermore, the influence of hydrological factors and geomorphology on the CWC distribution was investigated. Eleven coral habitats, formed by 62 morphotypes of scleractinians, gorgonians, antipatharians and seapens, inhabiting hard and/or soft substrate, were observed. The distribution patterns were heterogenous at regional and local scales; the south Bay of Biscay and the southeastern flank favored soft substrate habitats. Biogenic and hard substrate habitats supported higher coral diversities than soft substrate habitats and had similar species compositions. A higher coral species turnover characterized soft substrate habitats. Substrate type was the most important driver of the patterns in both distribution and composition. Observations of coral reefs on steeper areas in the canyons and coral rubble on flatter areas on the interfluve/upper slope support the hypothesis that canyons serve as refuges, being less accessible to trawling, although natural causes may also contribute to the explanation of this distribution pattern. The results of this study fed into a proposal of a Natura 2000 network in the Bay of Biscay where management plans are rare.

Cold‐water coral assemblages on vertical walls from the Northeast Atlantic

“…In tropical coral reefs, corals are often more abundant on vertical surfaces, where competition with algae and sedimentation rates may be reduced (Birkeland, 1977;Rogers, Fitz, Gilnack, Beets, & Hardin, 1984;Sheppard, 1982). Rich and abundant communities of suspension feeders on vertical walls have also been reported for deeper waters (Haedrich & Gagnon, 1991), but it is only in recent years that technological advances, particularly the increasing use of remotely operated vehicles (ROV), have allowed for more detailed descriptions of such environments (Bell, Alt, & Jones, 2016;Huvenne et al, 2011;Johnson et al, 2013) As a result, large vertical reefs of overhanging scleractinians (Brooke & Ross, 2014;Fabri et al, 2014;Huvenne et al, 2011;Van den Beld et al, 2017) and walls inhabited by Alcyonacea (Brooke et al, 2017;Edinger et al, 2011;Quattrini et al, 2015) or dominated by other community types such as bivalves (Johnson et al, 2013;Ludvigsen, Sortland, Johnsen, & Singh, 2007) and sponges (Bell et al, 2016;Brooke et al, 2017;Genin, Paull, & Dillon, 1992) are being discovered. Some of these steep walls have been reported as harbouring the highest abundances of corals or bivalves in the area (Gasbarro, Wan, & Tunnicliffe, 2018;Johnson et al, 2013;Morris, Tyler, Masson, Huvenne, & Rogers, 2013) with high numbers of other associated species also observed (Robert, Jones, Tyler, Rooij, & Huvenne, 2015).…”

Determining Coral Density Thresholds for Identifying Structurally Complex Vulnerable Marine Ecosystems in the Deep Sea

“…However, we are unaware of any published study that has examined the direct relationship between density parameters of cold-water coral reefs and the richness of associated species [but see acknowledgments, and Beazley et al (2015) and Ashford et al (2019) for examinations of the density/biomass of other VME indicatar taxa and associated species richness]. A study by Van Den Beld et al (2017) examined the separate relationships between stony coral cover and the abundance (but not species richness) of solitary coral taxa, and no density threshold for the abundances of these taxa was observed.…”

Influence of Water Masses on the Biodiversity and Biogeography of Deep-Sea Benthic Ecosystems in the North Atlantic

“…This water mass is easily identified by its high silicate concentration (McCartney, 1992). Whilst it is more prevalent in southern areas, a diluted form is also seen in the eastern subpolar basins (Van Aken and De Boer, 1995;New and Smythe-Wright, 2001).…”