Genetic structure and population connectivity of the deepsea file clam Acesta from submarine canyons in the North Atlantic

• Autor(a) principal: Pinho, Raquel Nunes de
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/28317
• topic: Acesta; Cold-water corals; Deep sea; mtCOI; Haplotype network

Advances in the exploration of the deep sea changed our view of an environment calm, dark and barren of life, to an environment where life presents adaptations to endure the extreme environmental conditions and prosper in habitats often hosting high biodiversity such as cold-water coral reefs (CWC). The calcium carbonate structure segregated by cold-water corals provides a 3D framework that offers shelter and resources for many species to establish, either permanently or temporarily. Increasing anthropogenic pressures related to the exploration of biological and mineral resources, especially the impacts of demersal trawling result in the disruption of this framework and ultimately affect the entire associated community. Impacts on CWC and associated fauna are serious enough to warrant global efforts to conserve these unique and fragile habitats, particularly through the establishment of marine protected areas (MPA’s). MPA design depends on estimates of connectivity and scales of dispersal for the taxa of interest, which is missing for most deep-sea species. The original objective of this study was to assess genetic connectivity between populations of the giant deep-sea clam Acesta excavata associated to CWC habitats in the European margin, in both reef formations and vertical walls of submarine canyons. However, the use of molecular methods, namely DNA barcoding, revealed the presence of another species of this genus associated to the cold-water coral Lophelia pertusa in the Whittard canyon (Celtic margin). This is the first report of Acesta cryptadelphe in the NE Atlantic, which until now was only known from the NW Atlantic. This unexpected result is a good example of the taxonomic issues that still persist in deep-sea ecosystems. Haplotype network analyses show that gene flow across the Atlantic Ocean is practically inexistent, but the existence of haplotypes that where not sampled raises the possibility of unknown populations of Acesta cryptadelphe in between the two margins, specifically in the Mid-Atlantic Ridge. Regarding Acesta excavata the analyses of sequences from two branches of the Whittard canyon show that, despite the complex topography and hydrography, there are no apparent barriers to gene flow between different branches of the canyon. Haplotype analyses reveal shared haplotypes between the Whittard canyon and the Norwegian margin and the Lisbon canyon suggesting a shared ancient polymorphism or present connectivity between locations. Genetic differentiation analyses are not conclusive, especially because of the low number of sequences available for Norway and the Lisbon canyon, but allow to establish different hypotheses that can be tested in the future, ideally using an integrative approach to understand connectivity. Connectivity along the European margin may be achieved through larvae dispersal, using different ocean currents as pathways of transport, and the presence of unknown populations acting as stepping-stones. Overall this thesis contributes with new knowledge and relevant data to support decisions to protect vulnerable habitats in the deep European margin.