Abstract
Seed burial in the sediment is critical for successful seedling establishment in seagrasses because it protects from predation and dispersal into unsuitable sites, and it may enhance germination by exposing the seeds to suitable germination stimuli. However, relatively little is known about the fate of buried seeds and their ability to emerge from greater depths. The goal of this study was to determine seed survival in the sediment, seedling emergence success and initial seedling biomass of Zostera marina in relation to burial depth and to evaluate if large seeds, having larger energy reserves, are more tolerant to burial than small seeds. Seeds from a perennial Z. marina population were buried at 7 different sediment depths (0.1–8 cm), and seeds sorted by size (large and small) were buried at depths of 2, 4 and 6 cm in outdoor mesocosms. Total seedling emergence after 2 months was significantly affected by seed burial depth, with maximum values in the top 2 cm of the sediment (48.1–56.7% of planted seeds), and a marked decline below 4 cm depth to only 5% seedling emergence at the deepest burial depth of 8 cm. Moreover, seeds had shorter time to emergence from shallow compared to deep burial depths. At all burial depths, a small fraction of seeds (<10%) died after germination but before emerging, and 15–30% remained viable after 6 months. Seed mortality was the major limitation to seedling recruitment from the deeper burial depths. The effect of seed size on seedling emergence success and time was not clear, but heavier seeds displayed greater longevity and gave rise to seedlings of significantly higher biomass, indicating that the mobilization of metabolic reserves may be important during initial seedling development.
Highlights
Zostera marina is a widespread and often dominant seagrass species in coastal and estuarine ecosystems across the northern hemisphere, where it fulfils important roles as ecosystem engineer and service provider [1,2]
In this study, seed germination leading to successful seedling emergence occurred at sediment depths down to 8 cm, but increasing seed burial depth severely reduced the number of emerging seedlings and delayed the time of emergence from sediment depths below 3 cm
Z. marina is regularly found at highly disturbed sites, where sediment dynamics caused by hydrodynamic forces or activity of burrowing animals may influence adult plant performance and re-establishment from seeds [12,28,52,53]
Summary
Zostera marina (eelgrass) is a widespread and often dominant seagrass species in coastal and estuarine ecosystems across the northern hemisphere, where it fulfils important roles as ecosystem engineer and service provider [1,2]. Widespread seagrass declines have led to increased. Z. marina can use both asexual and sexual reproduction to recover from disturbances. While clonal growth is the principal mode for sustaining persistent meadows, sexual recruitment plays a vital role in population expansion and recovery, and is necessary for the colonization of areas outside the range of vegetative growth [6,7,8,9]. Sexual recruitment influences population connectivity and contributes to increased genetic variation, which may enhance long-term resilience to stress [10]
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