Genetic diversity of the green macroalga Ulva linza in Kattegat and the Baltic sea with recommendations for aquaculture

Abstract

Genetic diversity is essential for the establishment of a sustainable seaweed aquaculture, as it serves as the foundation for population health and resilience to environmental stressors. The interest in green algal species cultivation has grown worldwide, particularly of the genus Ulva, commonly known as sea lettuces. Ulva is characterized by a haplodiplontic life cycle, with partially clonal reproduction. The mode of reproduction, sexual versus asexual, affects the genetic composition of a population and thereby shaping its ecological success and adaptive capacity. In this MSc thesis, the genetic diversity of U. linza was assessed and clonal lineages were characterized along the salinity gradient of Skagerrak, Kattegat, Öresund, and the Baltic Sea. To assess the genetic variation, 67 samples of U. linza were genotyped with 21,205 2b-RAD derived single nucleotide polymorphisms (SNPs). Overall, clonality was high. Among the 67 samples, 31 multilocus genotypes (MLG) were identified, two of which comprised 10 ramets each. Individuals in the Baltic Sea are predominantly clonal and genetic diversity in this region is low. In contrast, the highest genetic diversity was identified in Kattegat and Öresund with several smaller clonal lineages. In the Baltic Sea, individuals belonging to the same clonal lineage showed a broad distribution. This is the first study outlining the genetic diversity of U. linza in the Nordics. The here identified clusters of clonality and genetic variation can be used for prioritizing genetic resources of populations for the recruitment of individuals for aquaculture practices.