Whole genome sequencing reveals interbay population structure of Saccharina latissima (sugar kelp) in southwest Iceland

The nearshore macroalgae Saccharina latissima (e. sugar kelp, isl. beltisthari) is abundant across the boreal arctic marine region, and has been receiving increased focus around Iceland for aquaculture and ecological engineering potential. While the ecological and economic importance of nearshore macroalgae have become increasingly clear, the amount of genomic and population connectivity insights for this group is exceptionally depauperate. We here report the first population genomic level analysis of S. latissima in Iceland, comparing individuals sampled around and within the largest bay in southwestern Iceland, Faxafloi. We see a clear segregation of nearshore and offshore genotypes around the bay, with distinct compositions to the North of the mouth of the bay that differ from the South. We also see evidence of potential hybridization of nearshore and offshore individuals occurring exclusively deep within the bay. These patterns suggest a dynamic biogeography impacting the population structure of S. latissima within the Faxafloi bay, and highlight the potential for local selection pressures to shape genetic composition across surprisingly small distances.