Investigating drivers of marine connectivity in the pink sea fan: implications for its conservation and the designation of Marine Protected Areas

Given the continued anthropogenic pressures placed upon the world’s oceans, and the pace at which they are changing the marine environment, never has there been a more pressing need to establish the ecological drivers of connectivity across a species’ geographic range. The aim of this thesis was to use Next-Generation Sequencing techniques to: characterise patterns of genetic connectivity in the temperate octocoral, the pink sea fan, Eunicella verrucosa; understand the possible contribution of this species’ seascape to driving such patterns, and explore the potential for this species to respond to thermal stress with ongoing climate change. To address these aims, the first part of this thesis details the assembly and annotation of the first genome for E. verrucosa, which formed an integral genomic resource for this research. From the genome, alignment of RAD-seq data produced 7,650 genome-wide SNPs. Both neutral loci (7,510 SNPs) and putatively adaptive loci (55 SNPs) indicated a geographic cline of genetic variation across the majority of this species Northeast Atlantic range, and across the Mediterranean-Atlantic boundary, shaped by the geographic positioning of sampling sites. Complimentary use of passive-particle modelling suggested that this widespread connectivity could be shaped by rare, longer dispersal events of propagules under certain oceanic conditions. An ex situ thermal exposure experiment and transcriptomic analysis enabled exploration of thermotolerance in this species and suggested reduced thermotolerance to low thermal stress, which led to greater expression of genes linked to the coral immune system. The influence of temperature was also highlighted through genotype-environment analysis, which suggested the presence of locally adapted genotypes to sea temperature. This thesis provides the first insight into the ecological drivers of genetic connectivity in the pink sea fan, information which is integral for beginning to predict this species’ response to ongoing oceanic warming. It also enables conservation managers to identify pink sea fan populations where effective conservation measures may be needed, such as future designation of Marine Protected Areas