Population Genomics of the Sugar Kelp Saccharina latissima

Student thesis: Doctoral ThesisDoctor of Philosophy (awarded by UHI)


Macroalgae are key foundation species in temperate waters where they provide a host of services to marine ecosystems and human socio-economic needs. Macroalgae also represent one of the fastest growing aquaculture sectors globally. Despite their importance, macroalgal communities are under increasing pressure from anthropogenic climate change and disturbance. Macroalgal cultivation represents a largely beneficial activity, however, risks from potential genetic interactions between farmed and wild populations have been raised. The growing interest in seaweed cultivation in Europe has highlighted the need for a greater understanding of genetic differentiation in species of interest in order to mitigate potentially detrimental farm to wild interactions, as well as to
inform the management and conservation of wild kelp forests in the face of a changing climate.
This thesis aimed to address this challenge through the investigation of genetic
differentiation and connectivity in the widespread foundation kelp species Saccharina latissima over a range of spatial scales and environmental gradients. The thesis first focussed on the methodological development of a genome-wide double-digest RADseq population library for S. latissima, and in particular in overcoming the developmental hurdles of high quality gDNA extraction from macroalgae. Panels of 12,144 and 9,222 SNPs were assembled and applied in a seascape genomic approach to investigate spatial patterns of diversity, connectivity, and adaptation in populations of S. latissima from the west coasts of Scotland and Sweden. The high resolution marker panel highlighted the
presence of hierarchical population structuring in both studies. In particular, population barriers were identified between northern, southern, and Clyde Sea populations in Scotland, and between the Southern Kattegat and central and northern populations along the Swedish west coast. Hydrographic dispersal modelling, in combination with the genomic data, highlighted the significant influence of oceanographic processes on genetic differentiation in Swedish S. latissima, and in particular on the isolation of populations in the southern Kattegat. Genetic differentiation was also observed across local and regional
scale environmental gradients. Results from genotype-environmental association (GEA) tests highlighted the influences of environmental heterogeneity, as well as oceanographic isolation, in driving multi-scale patterns of local adaptation. Comparisons of the two genomic datasets highlighted contrasting levels of polymorphism and diversity, with the Scottish population harbouring higher levels of genome-wide polymorphism and minor alleles amongst populations. The divergent population histories of the two datasets also highlighted the strong influence of demographic and expansion history on genomic data
assembly and identified potential risks and biases from assembling genomic datasets from distant and divergent populations.
The findings from the thesis fed into recommended guidelines for the genetic
management of macroalgal cultivation in Scotland, and laid the groundwork for
preliminary breeding efforts in S. latissima. The investigation also contributed to a growing understanding of the patterns, scales, and influences on local adaptation in macroalgae, and offered important insights for the management and maintenance of functional genetic diversity in kelp forest ecosystems in response to intensifying environmental pressures.
Date of Award24 Aug 2021
Original languageEnglish
Awarding Institution
  • University of the Highlands and Islands
SupervisorMichele Stanley (Supervisor)

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