Functioning and vulnerability of continental slope ecosystems: combining stable isotope and visual survey approaches

• Main Author: Vieira, Rui Pedro Silva
• Format: Thesis
• Language: English
• Published: University of Southampton 2017
• Subjects: Porcupine Seabight; North East Atlantic
• Online Access: https://eprints.soton.ac.uk/415531/; https://eprints.soton.ac.uk/415531/1/Vieira_Rui_PhD_Thesis_2017.pdf

Continental slopes support highly diverse ecosystems, influenced by strong environmental depth-related gradients, but many fundamental aspects of ecosystem dynamics remain poorly understood. Emerging evidences show that human-driven pressures are a primary reason for rapid and unpredictable changes on deep-sea ecosystems. For this reason, it is important to understand the ecological drivers behind community dynamics to improve our ability for a sustainable use and to mitigate impacts. In a multidisciplinary context, I aimed to explore aspects of continental slope ecosystem functioning, including trophic ecology, community structure and function, and potential human-induced perturbations. I used stable isotope analysis to investigate ecological drivers explaining demersal fish community structure between 500 and 2000 m water depth on the North East Atlantic (Scottish and Irish) continental slope. I show that community-level predator prey mass ratios are invariant along a strong environmental gradient and between feeding behaviours. Results also suggest that body size is responsible for a large proportion of the isotopic niche areas and revealed the effect of increasing depth in resource partitioning, with an indication of a divergent energy supply pathways. Finally, I assessed the present status of an important deepwater vulnerable marine ecosystem in the Porcupine Seabight (NE Atlantic). The Porcupine Seabight was surveyed extensively between 1977 and 1986 and was revisited in 2011 to compare the spatial coverage and size distributions of hexactinellid sponges (Pheronema carpenteri) as an indicator for trawling impact. I found that deep-sea sponge aggregations (a) are still present in the Porcupine Seabight, and (b) do appear to be vulnerable to / under threat from deep-water trawl fishing. In conclusion, it is shown that isotope-type metrics may be powerful proxies to understand community structure and a useful tool to improve ecosystem-based models. Results here present are suggestive that changes in benthic ...