Saccharina sporophytes settling on kelp cultivation rafts come from wild intertidal populations and not from the farmed cultivars

Wild-type sporophytes of Saccharina japonica have been recurrently observed on the infrastructures of kelp farming rafts in China’s northern production region (Liaoning and Shandong provinces). However, there are few detailed reports delineating their origin, genetic attributes and affiliations with farmed populations. Using microsatellite molecular analyses, we furnish a comparative analysis of the populations sampled from these rafts at one of the historical kelp farming regions Rongcheng city (Shandong province), both before and after the “2021–2022 kelp farming disaster”, in conjunction with two field populations from nearby intertidal zones where natural populations prevail. The results show that the wild kelp populations on the kelp farming rafts in 2023 had originated from the wild populations dwelling in intertidal zones several kilometers away, rather than from the artificially cultivated kelp cultivars.