Effects of Seed Source, Sediment Type, and Burial Depth on Mixed-Annual and Perennial Zostera marina L. Seed Germination and Seedling Establishment

Seed germination and seedling establishment directly affect the resiliency of seagrasses to disturbance or environmental stress. The objectives of this study were to compare maximum seed germination, time to germination, nongerminated seed viability, and initial seedling biomass between mixed-annual and perennial Zostera marina seed populations in coarse (> 90 % sand) and fine (< 50 % sand) sediments and at shallow (1 cm) and deep (5 cm) burial depths. Perennial seeds collected from Virginia and North Carolina had greater maximum germination, shorter time to germination, and greater seedling biomass compared to mixed-annual seeds collected from North Carolina. For both mixed-annual and perennial seeds, maximum germination and seedling biomass were the greatest in shallow fine sediments. Mixed-annual seeds buried at 1 cm had a shorter time to germination than in the deep treatments; however, sediment type did not affect mean time to germination. Perennial seeds had a shorter time to germination in shallow compared to deep burial depths and in fine compared to coarse sediments. Cues for germination were present at the deeper depths; however, the cotyledon failed to emerge from the sediment surface resulting in mortality at depths of 5 cm. The greater performance of perennial compared to mixed-annual seeds and seedlings demonstrate the trade-offs which can occur between Z. marina reproductive strategies. Reduced germination of Z. marina seeds buried a parts per thousand yen5 cm and in coarse sediments may represent a possible bottleneck in successful sexual reproduction, feasibly affecting the resiliency to and recovery from disturbance for both perennial and mixed-annual Z. marina beds.