Kelp, Saccharina spp, population genetics in New England, US, for guiding a breeding program of thermally resilient strains

The cold-water sugar kelp, Saccharina latissima has a circumboreal distribution and in the Northwest Atlantic is at its southern distributional limits in Long Island Sound. An understanding of genetic diversity of natural kelp populations is critical for making recommendations for breeding and cultivation efforts of the growing seaweed aquaculture sector in the US. An important component of the ARPA-E’s MARINER project is selectively breeding Saccharina spp. in order to improve overall productivity for biofuels, feeds and food. 　Historical records indicate the presence of regional kelp ecotypes based on physiological tolerance, specifically temperature. We made collections of 15 wild Saccharina spp. populations via SCUBA along the New England coast. Microscopic gametophytes were isolated and the parental populations were used to make over 500 hybrid crosses that were planted at several farm locations over several years. We then used genome-wide single nucleotide polymorphism data to explore the genetic structure of the kelp throughout this region. An assessment of the sequence diversity revealed distinct genetic variation between the Gulf of Maine and Southern New England (FST > 0.25), confirming that Cape Cod acts as a barrier to S. latissima gene flow. Furthermore, based on the analysis of molecular variance (AMOVA), we found the largest variance (58%) within sites. We also observed admixture among three ancestral populations and isolation by distance. Future steps for this project include skim sequencing the haploid microscopic gametophytes to identify trait heritability, phenotypic diversity observed for both morphological traits and tissue composition, and genomic selection. Furthermore, in the future, we plan to place our sequence data into a larger context to include samples from sites in the east Atlantic and Pacific Oceans.