Extended storage of Posidonia oceanica seeds and seedlings: A breakthrough for year-round seagrass restoration

Seagrass meadows are experiencing global declines due to a combination of human-induced pressures and natural disturbances, resulting in the loss of critical ecosystem services. In the Mediterranean, Posidonia oceanica meadows represent one of the most productive coastal ecosystems. Traditional restoration approaches rely on lateral cuttings, which are costly, labor-intensive, impacting donor meadows, and restrictive in terms of genetic diversity. Seed-based propagation offers a promising alternative, preserving genetic variability; however, it is limited by the unpredictability of seed stranding events and the brief timeframe for seed collection and transplantation. To overcome these constraints, we investigated long-term storage methods for seeds and seedlings, aiming to extend restoration windows beyond natural germination periods. Specifically, we assessed the effects of light conditions, storage density, and seedling developmental stage on viability during six months of cold storage at 4 degrees C. Our findings show that light is essential for maintaining viability, as all seedlings stored in darkness failed to survive. Seedlings aged 1-2 months exhibited significantly higher survival rates (70-90 %) than freshly collected seeds (40 %), while density had no notable impact on viability, supporting scalability. Attempts to induce dormancy using abscisic acid (ABA) and paclobutrazol were ineffective. This study presents the first successful protocol for extended storage of P. oceanica seeds and seedlings, offering a practical tool to improve the flexibility, feasibility, and efficiency of seagrass restoration efforts throughout the year.