The deep sea refers to areas of the ocean below 200 metres and is both relatively and classed as highly vulnerable as a result of anthropogenic activities. Submarine canyons, in particular, are complex topographical features and conduits to the deep ocean and are particuarly at risk from human activity such as fishing and marine litter impacts.
List of Dissertations
The following are the abstracts from past dissertations at the University of Gibraltar.
Marine litter in submarine canyons: A case study of the SW Approaches
Marine litter is not only an aesthetic concern, but it also poses serious environmental problems on the seabed. It has been found in every marine environment without exception and at all depths, even in the deepest parts of the ocean. Marine litter is also a concern in submarine canyons, known for being biodiversity hotspots. They are considered to be preferential conduits of sediments and organic matter, connecting the continental shelf with the abyssal plain. The oceanographic processes responsible for the transport of matter are also responsible for submarine canyons being considered depocentres for marine litter.
Research into marine litter in submarine canyons and the deep sea in general is still in its infancy. A literature review selecting studies with primary data of benthic marine litter at depths of over 50 m revealed important gaps in the knowledge, and a requirement for a standardised system to classify, enumerate and identify marine litter to make studies comparable. There is also a need to adopt a more rigorous approach to recording interactions of litter with biota on the benthos. A comprehensive case study was carried out using high resolution data provided by a 2017 survey of the SW Approaches using a drop frame camera. Video data were analysed using BIIGLE software and litter was
classified using the classification system provided by OSPAR standardised by the MSFD. Data analysis revealed a mean litter density of 7,268 items/km2 ±17378 in the SW Approaches. This is driven by high mean densities in the interfluve areas, with 5.1 times higher density on the interfluves (9446 items/km2± 17570) than inside the canyon areas (1835 items/km2 ±2551). ANOSIM analyses support these findings and show significant differences between groups inside and outside of the canyons when looking at depth and morphological settings. The differences between areas were driven by litter density variations, as the composition of litter was more homogenous between the canyons and in different parts of the canyons. Marine litter in the SW Approaches, especially the interfluves, is very much affected by fishing activities despite it lying in a designated MCZ. Over 97.3% of the litter is derelict fishing gear, the highest proportion of any canyon studied to date.
Secondary Supervisors: Dr Jaime Davies, University of Plymouth,
Dr Veerle Huvenne (National Oceanography Centre, Southampton).
The Alice Project: Assessment of Litter-fauna Interactions in submarine Canyon Environments
Litter is ubiquitous in the ocean, interacting with fauna and causing impacts that are unquantified at present. Mainly sourced from land, marine litter is very persistent, experiencing slow degradation upon settling on the ocean floor. Submarine canyons contain more litter than other oceanographic features due to hydrological processes, but study of litter in canyons is made difficult by logistical requirements. Monitoring and quantification of marine litter often do not consider interactions between fauna and the litter, meaning impacts are largely unconsidered and unknown. Among publications that have reported L-F interactions in canyons, the large majority occur in the Mediterranean Sea, and the most commonly reported interaction is of corals entangled in fishing gear. When it occurs, the reporting of L-F interactions is unstandardised, resulting in a lack of global comparison and trend analysis. A standardised, comprehensive framework for the
reporting of L-F interactions has been created and includes 6 major categories: entanglement, ingestion, smothering, habitat provision, adaptive behaviour, and
encountering. Entanglement and smothering can occur on abiotic features as well.
Use of the framework will aid in research collaboration and creation of a global
dataset of L-F interactions. Impacts resulting from interactions are plentiful, most coming from entanglement and smothering. In a case study of The Canyons Marine Conservation Zone (MCZ), a British offshore site containing two submarine canyons, the most commonly observed interactions are anemones encountering litter in non-contact manners, hydroids growing on litter, and cold-water corals (CWCs) both in contact with and being entangled by litter. From the interactions occurring, it is proposed that The Canyons MCZ is most impacted by damage to its CWCs, which are the only CWCs found in British waters. When in contact with litter, corals can experience lesions, breaking, and death. In order to limit the L-F interactions occurring, the most effective strategy is to prevent the accumulation of marine litter. Large infrastructure shifts will be required to lessen marine litter inputs, including creation of cyclical production and consumption cycles and improved waste management capabilities globally.
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