Cintia Iha1,2, Cayne Layton2, Carlos E. Amancio3, Warren Flentje4, Andrew Lenton5, Ceridwen I. Fraser6, Craig Johnson2 and Anusuya Willis1
1 Australian National Algae Culture Collection ANACC, CSIRO, National Collections and Marine Infrastructure, Hobart, TAS, Australia
2 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia
3 Independent researcher, São Paulo, SP, Brazil
4 Mineral Resources, CSIRO, Parkville, VIC, Australia
5 Permanent Carbon Locking Future Science Platform, Oceans and Atmosphere, CSIRO, Hobart, TAS, Australia
6 Department of Marine Science, University of Otago, New Zealand
Macrocystis pyrifera forms dense kelp forests creating complex habitats that support coastal productivity and other essential ecosystem services. Tasmanian coasts have lost ~95% of their giant kelp forests in the last decades due to changes in climate and other environmental conditions, such as ocean warming. Recent restoration efforts demonstrated that some lineages of Tasmanian giant kelp possess increased tolerance to warmer waters. Little is known about the genetic structure of these giant kelp populations, particularly warm-tolerant individuals; this knowledge is crucial for building a management plan for kelp forest conservation and restoration. Here, we assess the genetic structure of Tasmanian giant kelp with genotyping-by-sequencing (GBS) and explore whether some genotypes correlate with warmth tolerance. Forty-five gametophyte cultures—originating from parental sporophytes collected at three northern and three southern populations of Tasmania—were used to perform GBS with ddRAD-based library preparation. The individuals from the north and the south are two genetically distinct populations, with genetic divergence also evident between sites within each region, particularly the southeast region. This result contradicts prior genetic analysis (using organellar markers or nuclear ITS), which suggested low genetic diversity among populations in Tasmania. Our results show that ten markers are potentially associated with warm tolerance. However, more genotyping markers were correlated to the absence of tolerance. Our findings reveal a higher genetic diversity of M. pyrifera than previously thought and provide an introductory foray to the challenges of using conservation genomics for endangered kelp forests to benefit their restoration and natural resource management.