Using genomics to design and evaluate the performance of underwater forest restoration

Restoration is an emerging intervention to reverse the degradation and loss of marine habitat-formers and the ecosystem services they underpin. Current best practice seeks to restore populations by transplanting donor individuals chosen to replicate genetic diversity and structure of extant, nearby populations. However, genetic characteristics are rarely empirically examined across generations, despite their potential role in influencing restoration success. We used genomics to design a restoration program for lost underwater forests ofPhyllospora comosa, a dominant forest-forming macroalga that went locally extinct from reefs off Sydney, Australia. Population genetic diversity and structure of nearby extant populations informed choice of donor sites. We tested whether donor provenance influenced adult transplant survival, condition (via metrics of epibiosis) and the genetic characteristics of recruits at restoration sites. Extant populations ofPhyllosporawithin a 100-km radius of Sydney comprised three distinct genetic clusters with similar levels of genetic diversity. We transplanted reproductive adults from two of these sites, with the aim of restoring fivePhyllosporaforests with levels of genetic structure and diversity similar to donor populations. Donor provenance influenced survival and condition of transplanted adults and recruitment levels varied significantly among restoration sites. Yet, recruitment was rapid and genetic diversity and structure of the F(1)generation resembled extant populations. This likely occurred because transplanted individuals reproduced synchronously and rapidly post-transplantation, prior to mortality of adult donor transplants. Synthesis and applications. As restoration and the need to 'future-proof' marine ecosystems increase globally, it will be critical to understand and harness the role of donor provenance, genetic diversity and structure in restoration success. By incorporating ecological and genomic data into restoration design and assessment, this study demonstrates that evidence-based selection of macroalgal donors can result in F(1)generation recruits with similar levels of genetic diversity and structure as extant populations, despite an effect of provenance on transplant survival and condition. This study also highlights the need for ongoing refinement of transplantation techniques to ensure future recruitment success.