Abstract
Fine-scale structural complexity created by reef-building coral in shallow-water environments is influential on biodiversity, species assemblage and functional trait expression. Cold-water coral reefs are also hotspots of biodiversity, often attributed to the hard surface and structural complexity provided by the coral. However, that complexity has seldom been quantified on a centimetric scale in cold-water coral reefs, unlike their shallow-water counterparts, and has therefore never been linked in a similar way to the reef inhabitant community. Structure from motion techniques which create high-resolution 3D models of habitats from sequences of photographs is being increasingly utilised, in tandem with 3D spatial analysis to create useful 3D metrics, such as rugosity. Here, we demonstrate the use of ROV video transect data for 3D reconstructions of cold-water coral reefs at depths of nearly 1000 m in the Explorer Canyon, a tributary of Whittard Canyon, NE Atlantic. We constructed 40 3D models of approximately 25-m-length video transects using Agisoft Photoscan software, resulting in sub-centimetre resolution reconstructions. Digital elevation models were utilised to derive rugosity metrics, and orthomosaics were used for coral coverage assessment. We found rugosity values comparable to shallow-water tropical coral reef rugosity. Reef and nearby non-reef communities differed in assemblage composition, which was driven by depth and rugosity. Species richness, epifauna abundance and fish abundance increased with structural complexity, being attributed to an increase in niches, food, shelter and alteration of physical water movement. Biodiversity plateaued at higher rugosity, illustrating the establishment of a specific reef community supported by more than 30% coral cover. The proportion of dead coral to live coral had limited influence on the community structure; instead, within-reef patterns were explained by depth and rugosity, though our results were confounded to a certain extent by multi-collinearity. Fine-scale structural complexity appeared to be integral to local-scale ecological patterns in cold-water coral reef communities.
Highlights
Some colonial Scleractinian cold-water corals, such as Lophelia pertusa (recently synonymised to Desmophyllum pertusum (Addamo et al 2016)), Madrepora oculata andCoral Reefs (2019) 38:1007–1021Solenosmillia variablis, are capable of forming complex 3D reef structures, ranging from patchy cover to massive carbonate mounds (Wilson 1979; Wheeler et al 2007)
We aim to (1) quantify the structural complexity introduced by cold-water coral reef patches (2) identify the role of structural complexity in driving biodiversity and assemblage composition (3) use fine-scale information to identify the threshold of coral cover and structural complexity required to form a distinct cold-water coral reef habitat and provide evidence for Vulnerable Marine Ecosystem (VME) characteristics
The canyon lies within the British exclusive economic zone (EEZ) and forms part of The Canyons Marine Conservation Zone (MCZ) (Ministerial order 2013) which was designated based on the occurrence of deep-sea bed and cold-water coral reef habitats in accordance with the UK Marine and Coastal Access Act (2009)
Summary
Some colonial Scleractinian cold-water corals, such as Lophelia pertusa (recently synonymised to Desmophyllum pertusum (Addamo et al 2016)), Madrepora oculata andCoral Reefs (2019) 38:1007–1021Solenosmillia variablis, are capable of forming complex 3D reef structures, ranging from patchy cover to massive carbonate mounds (Wilson 1979; Wheeler et al 2007). Cold-water coral reefs are predominantly found on continental slopes, seamounts and in fjords, but increasing evidence suggests submarine canyons provide an important habitat (Orejas et al 2009; Huvenne et al 2011; De Mol et al 2011; Lo Iacono et al 2018) Due to their complex terrain, submarine canyons may provide important refugia for cold-water coral assemblages (Huvenne et al 2011) that are vulnerable to destructive fishing practices elsewhere (Fossa et al 2002; Davies et al 2007; Althaus et al 2009; Huvenne et al 2016a). Shannon–Wiener indices of taxa associated with cold-water coral reefs on the Faroe shelves (North Atlantic) were approximately 5.5, a value which is comparable with shallow-water reef biodiversity (Jensen and Frederiksen 1992) This biodiversity is associated with sessile and vagile taxa alike (Jonsson et al 2004). The structural complexity of the 3D framework provided by the coral skeleton is considered an important variable contributing to cold-water coral reef assemblage and biodiversity (Jonsson et al 2004; Cordes et al 2008; Robert et al 2017)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
