Adaptive management and long-term monitoring approaches achieve first functional seagrass meadow restoration in Cockburn Sound, Western Australia

Seagrasses are increasingly impacted by dredging activities and coastal development, yet successful large-scale mitigation is rare. Seagrass restoration efforts to date usually involve transplanting ‘borrowing’ plant material from one meadow to form another, generally resulting in a net loss when the restoration fails. Just over three hectares (31,000m 2 ) of seagrass were transplanted and subsequently monitored over a period of eight years in Cockburn Sound, Western Australia, to mitigate the impacts of lime-sand dredging and harbour development. This study assessed the viability of transplanting local meadow-forming species, Posidonia australis and identified key factors influencing transplantation success. Five years after planting total sprig survival over three hectares was more than 85% (areal cover); although survival was variable within the 3.1 hectares. Plantings utilising improved techniques and sprig quality showed over 90% coverage after 2.5 years; previous techniques achieved 75% coverage after 3.5 years. All surviving sprigs spread rapidly and started merging with adjacent sprigs after two years. Flowering of transplanted sprigs occurred 3.5 years after initial plantings. After eight years shoot densities had increased from 18 ± 2.1 shoots m -2 to 503.7 ± 16.9 shoots m -2 , resembling nearby natural meadows. Evidence of natural recruitment was also observed both within and beyond the transplanted area. These findings demonstrate that large-scale seagrass rehabilitation is achievable and resilient, even in relatively exposed coastal environments. This work provides a valuable model for future restoration initiatives, contributing to the broader goal of conserving and restoring seagrass ecosystems at scale.