The importance of genetic make-up in seagrass restoration:A case study of the seagrass <i>Zostera noltei</i>

Seagrass meadows are among the most important coastal ecosystems. Their ongoing decline is of concern, and transplantations are carried out in many parts of the world to restore the ecosystem services seagrass meadows provide. Several studies have highlighted the importance of genetic diversity for transplantation success in seagrasses, but this is still rarely taken into account in transplantation trials. Here we assess a transplantation experiment of the seagrass Zostera noltei in one of the largest saline Mediterranean lagoons 4 yr after transplantations were carried out with low success rates. We compare genetic diversity values of a transplant site, 2 relict meadows and newly appeared patches in the lagoon to genetic diversity metrics measured before the transplantation experiment inside and outside the lagoon. We show that genotypic richness of the transplant site assessed 4 yr after the transplantation is very low. Moreover, the transplants are genetically distinct from the genetic stock in the lagoon, with low migration rates, low effective population size and signs of a recent population bottleneck. Relict meadows and newly appeared patches show, in contrast, signs of high levels of sexual reproduction and are connected via gene flow. The newly appeared patches likely did not originate from the transplantation. The lack of success of transplanted shoots could be due to an adaptation mismatch of the marine donor material to lagoon conditions or to low plasticity of the transplanted shoots.