Multi-scale investigations of cold-water coral habitat using novel technology and advanced image analysis

Abstract

Cold-water corals, like their shallow-water counterparts are capable of forming reef habitats that are important for their local environment. Cold-water corals are under increasing anthropogenic pressure and thus, the need to map their occurrence and understand their fundamental ecological role is essential in order to plan effective conservation measures. Cold-water coral reefs promote biodiversity with the introduction of structural complexity and substrate heterogeneity. Whilst the role of structural complexity is important and is a key criterion of Vulnerable Marine Ecosystem designation, we typically lack high-resolution data that can quantify such metrics. Ship-borne multibeam echosounder (MBES) data is typically low resolution, missing vital geomorphological features and the detailed video coverage is minimal in comparison. This results in Ill-matched datasets for mapping coral extent through predictive mapping and insufficient resolution to quantify cold-water coral reef structural complexity. We deployed an Autonomous Underwater Vehicle (AUV) to collect high-resolution MBES data and Remotely Operated Vehicles to collect images for Structure from Motion (SfM) to bridge the gaps in data resolution and undertake novel fine-scale investigations. We aimed to utilise high resolution data to accurately predict cold-water coral distribution and to use 3D photogrammetry to quantify the influence of cold-water coral reef structure on associated taxa diversity and distribution.
The results in this thesis show that by resolving fine-scale geomorphological features with high-resolution bathymetry, additional locations suitable for cold-water coral growth can be identified. The results further highlighted the importance of vertical walls in Explorer Canyon, NE Atlantic, as a habitat for cold-water coral. This thesis also demonstrates how SfM can be used to quantify cold-water coral structural complexity. Cold-water coral reef in Explorer Canyon introduces significant structural complexity on a centimetric scale, promoting local biodiversity and providing a distinct cold-water coral habitat when coral coverage was greater than 30%. Further investigations reveal that cold-water coral associated taxa are not randomly distributed within cold-water coral reefs, instead local geomorphic properties such as rugosity and inferred biotic interactions are conducive to localised clustering of reef associated species. The combination of scales of analysis quantitively depict how important cold-water coral are to their local environment and more accurately indicate their true spatial extent providing useful information for marine spatial planning.

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ORCID for Veerle Huvenne: orcid.org/0000-0001-7135-6360

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