The use of Zostera marina (eelgrass) seeds for seagrass restoration is increasingly recognized as an alternative to transplanting shoots as losses of seagrass habitat generate interest in large-scale restoration. We explored new techniques for efficient large-scale restoration of Z. marina using seeds by addressing the factors limiting seed collection, processing, survival, and distribution. We tested an existing mechanical harvesting system for expanding the scale of seed collections, and developed and evaluated two new experimental systems. A seeding technique using buoys holding reproductive shoots at restoration sites to eliminate seed storage was tested along with new techniques for reducing seed-processing labor. A series of experiments evaluated storage conditions that maintain viability of seeds during summer storage for fall planting. Finally, a new mechanical seed-planting technique appropriate for large scales was developed and tested.
Mechanical harvesting was an effective approach for collecting seeds, and impacts on donor beds were low. Deploying seed-bearing shoots in buoys produced fewer seedlings and required more effort than isolating, storing, and hand-broadcasting seeds in the fall. We show that viable seeds can be separated from grass wrack based on seed fall velocity and that seed survival during storage can be high (92–95% survival over 3 months). Mechanical seed-planting did not enhance seedling establishment at our sites, but may be a useful tool for evaluating restoration sites. Our work demonstrates the potential for expanding the scale of seed-based Z. marina restoration but the limiting factor remains the low rate of initial seedling establishment from broadcast seeds.