Successful Establishment of Restored Seagrass Meadows Revealed by Photosynthetic Performance: A Diving-PAM Study of Zostera marina in Dadohaehaesang National Park, Korea

Seagrass restoration has been widely implemented to recover degraded coastal ecosystems; however, evaluating the establishment success of restored populations remains a key challenge. This study assessed the establishment status of restored eelgrass (Zostera marina) meadows by comparing their photosynthetic performance and growth characteristics with those of natural populations across five coastal sites (Byeonchon of Geomun-do, Wolhang Harbor and Soan Harbor of Soan-do, Gaemeori Harbor of Hwaetae-do, and Dangrak-ri Harbor of Cheongsan-do) in Dadohaehaesang National Park, Korea. Photosynthetic parameters were measured in situ using a Diving-PAM fluorometer, including maximum quantum yield (Fv/Fm), relative electron transport rate (rETR), maximum electron transport rate (rETRmax), and the light saturation parameter (Ek). In addition, shoot density, morphological characteristics, and environmental variables were investigated to evaluate the ecological status of the eelgrass meadows. Water temperature ranged from 15.6 to 20.6°C and salinity from 32.20 to 32.47, indicating relatively stable marine conditions across the study sites. Dissolved oxygen concentrations ranged from 7.00 to 11.23 mgL⁻¹, with supersaturation observed at some locations. Dissolved inorganic nutrients and sediment characteristics showed spatial variability among sites, reflecting heterogeneity in local environmental conditions. Despite these environmental differences, the maximum quantum yield (Fv/Fm) ranged from 0.75 to 0.77 in both natural and restored meadows, with no significant difference between meadow types. These values indicate a healthy photosynthetic condition in which photosystem II functions normally. Although rETR and rETRmax exhibited some variability among sites, restored meadows generally showed values comparable to those observed in natural meadows. Estimated carbon-based primary production ranged from 31.60 to 54.00 mg C m⁻² h⁻¹ in natural meadows and from 29.85 to 48.41 mg C m⁻² h⁻¹ in restored meadows, suggesting that restored populations have achieved functional photosynthetic productivity comparable to natural eelgrass beds. Shoot density and the proportion of flowering shoots did not show clear differences between natural and restored meadows, indicating that restored populations have developed structural and reproductive characteristics similar to those of natural populations. Overall, these results demonstrate that restored eelgrass meadows in Dadohaehaesang National Park have reached physiological and functional conditions comparable to natural meadows and have been successfully established. Furthermore, the use of Diving-PAM fluorescence measurements provides a rapid and effective approach for assessing the physiological status and restoration success of seagrass populations, highlighting its potential as a valuable monitoring tool in seagrass restoration programs.