Genetic diversity, structure, and connectivity of Laminaria hyperborea in Norway, using SNP analysis

Kelps (order Laminariales) are crucial foundation species providing vital ecosystem services and supporting rich biodiversity amidst a biodiversity crisis. However, kelp forests are in global decline due to climatic stress and other human impacts. In kelp forests, higher genetic diversity, allelic richness (AR) and expected heterozygosity (HE), in a distinct population are associated with climatic resilience. Thus, identifying populations from analysis of genetic structure, and the genetic diversity therein, is essential for understanding the resilience of kelp forests to forecasted climate stress and for effective conservation. Here, we document the first analysis of the population structure, genetic diversity, and connectivity of the kelp forest species Laminaria hyperborea using single nucleotide polymorphisms (SNPs). We employed double digest restriction-site associated DNA (ddRAD) sequencing to identify 12,345 SNPs from 143 individuals across 15 sites spanning about 2200 km of outer coastline in Norway. Cluster analysis identified seven ancestral populations, which represents a higher degree of population structure than previously reported using microsatellites. Kelps at each site exhibited low genetic diversity, high differentiation, weak isolation by distance, and low to moderate connectivity. Allelic richness and heterozygosity generally decreased toward the south, with one southern population showing the highest genetic diversity. Despite being considered a potential thermal refuge under future conditions, populations of L. hyperborea in Norway, especially in Skagerrak, likely have low genetic resilience to climatic stress. Immediate management is likely necessary to preserve, conserve, and restore some of the central and southern populations with low genetic diversity to prepare for increasingly adverse conditions affecting L. hyperborea and the coastal ecosystems dependent on healthy kelp forests.