Sustainable Kelp Aquaculture in Sweden

Abstract: Seaweed aquaculture is gaining more interest worldwide, including Europe. However, despite its long coast seaweed farming is still very minor in Sweden. The overarching aim of this thesis is to develop sustainable cultivation methods for Sugar kelp (Saccharina latissima) in Sweden, with more specific focus on (1) the effect of seaweed farming on ecosystem services and its environmental impact, (2) spatial location of farm sites, and (3) the development of new techniques and knowledge for selective breeding programs. An ecosystem services assessment combined with the analysis of various environmental parameters in the field were used to study environmental impact associated with a two-hectare kelp farm. The ecosystem services assessment indicated positive or no effect on provisioning (e.g. food, biomaterials), supporting (e.g. habitat, biodiversity), and regulating (e.g. mitigating eutrophication) ecosystem services. However, some cultural ecosystem services such as recreation and aesthetic values, were likely negatively affected. The results from the environmental impact study showed that the seaweed farm has very limited negative environmental effects, but can rather have a positive effect on some environmental parameters. The selection of suitable cultivation sites in coastal waters is essential for the sustainable establishment and further development of seaweed aquaculture in previously unexplored regions. In two field studies I investigated spatial growth patterns of S. latissima for optimising its nutrient mitigation capacity, crop yield, and crop quality (i.e. biofouling). The results indicate that there is relatively large spatial variation in growth and nutrient mitigation capacity of farmed seaweed biomass. Biofouling and growth decreased with increasing exposure levels, indicating that wave exposure is an important factor for site selection. Furthermore, the capacity to conserve genetic diversity through cryo-preservation of gametophytic cells (i.e. haploid life stage) was found to be an attractive preservation method. The results show that after thawing the preserved gametophytes may serve as seed stock for onward cultivation or in selective breeding programs. A successful domestication commonly starts with a base knowledge of the genetic population structure and diversity of the species of interest. Therefore, this was assessed for S. latissima along the Swedish west coast, using genomic sequencing (ddRAD). The results suggest a well-connected meta-population along the Swedish west coast, but with clear signals of adaptive divergence between sub-populations, most likely driven by environmental selection. This indicates strong natural selection in the heterogeneous marine coastal environment, leading to local adaptations despite high gene flow and connectivity.