Variation in seed germination and early seedling development of Zostera marina across source populations and environmental conditions

Seagrass ( Zostera marina ), a key provider of essential marine ecosystem services, is experiencing global decline. A deeper understanding of seed traits and the environmental factors influencing germination and early seedling development is critical for enhancing seed-based restoration efforts. In this study, we quantified the seed characteristics across five Z. marina populations along the Korean coastline. Field and controlled laboratory experiments were conducted to assess the effects of seed source population, salinity (0, 15, 30 PSU), and temperature (5, 10, 20°C) on germination performance and seedling development. Seed size traits varied significantly among populations, even between annual and perennial populations within the same bay system. Seed source populations with different life history strategies and seed size had a pronounced influence on germination and early seedling development. Annual seeds exhibited superior germination performance, including higher maximum germination rate (MGR), shorter mean time to germination (MTG), and faster early seedling development compared to perennials. Post-seedling growth benefited from large seeds across all populations. Germination was generally inhibited by high temperature (20°C) and low salinity (0 and 15 PSU), resulting in lower MGR compared to seeds exposed to optimal conditions (10°C and 30 PSU). These findings provide crucial insights into the variability of germination performance and early seedling development among seed source populations and their responses to varying salinity and temperature conditions. This study offers valuable information for Z. marina restoration efforts using the seed-based method, particularly concerning seed source selection and climate change-driven environmental shifts.