Seedling establishment in eelgrass: seed burial effects on winter losses of developing seedlings

Abstract

Constraints on the transition of seeds to seedlings have the potential to control plant dispersal and persistence. We investigated the processes leading to low initial seedling establishment in eelgrass Zostera marina through a manipulative field experiment assessing the relative importance of germination failure and seedling loss during the winter. Seed plots were established in October at 3 unvegetated sites in the Chesapeake Bay (USA) region, with seeds either at the sediment surface or buried at 2 to 3 cm. Emerging seedlings were monitored at 6 wk intervals between December and April using a video camera, and seed germination was tracked in separate destructively-sampled plots. Sediment height change was measured, and sediment disturbance depth was estimated by deploying cores layered with tracer particles and examining tracer loss upon core retrieval. We found a low rate of seedling establishment 6 mo after seeding (1.2, 3.8, and 2.8% for surface seeds at the 3 sites) that was largely due to seed and seedling loss rather than to germination failure, with 90% of seeds retrieved after December having germinated. Seed burial significantly enhanced seedling establishment at 2 of 3 sites (40.4, 16.8, and 10.3% establishment for buried seeds). Seed loss occurred mostly within the first month of the experiment, and was most severe for seeds at the sediment surface. Indicator core results showed widespread disturbance of sediments to depths that could have dislodged early seedlings developing from surface seeds, and to a lesser degree seedlings from buried seeds. Our findings help identify the nature and timing of a substantial Z. marina seedling establishment bottleneck in our region, and show that some of the key processes pivotal to Z. marina recruitment dynamics and optimal restoration strategies involve physical sediment−seedling interactions rather than seed germination.

Seed Predation by the Shore Crab Carcinus maenas: A Positive Feedback Preventing Eelgrass Recovery?

“…Seeds planted at 2 cm depth have shown higher germination and seedling survival than at deeper depths or at the sediment surface [28,55–57]. Seeds can be naturally buried in the sediment by processes such as sediment dynamics driven by hydrodynamics and sediment reworking by the lugworm Arenicola marina [41,52].…”

Seed germination in a southern Australian temperate seagrass

“…Seed germination is a potential limiting stage in successful sexual reproduction for both terrestrial (Harper, 1977) and marine angiosperms (Jarvis & Moore, 2015; Marion & Orth, 2012; Orth et al, 2000). Germination failure has predominantly been related to the characteristics of the surrounding microenvironment which may lack the required signals to break seed dormancy, which can last up to 12 months for other Zostera species (Orth et al, 2000), and initiate germination (Baskin & Baskin, 2014).…”

Interactive effects between physical forces and ecosystem engineers on seed burial: a case study using Spartina anglica

“…More recently, seed burial has been demonstrated to be vital to seedling establishment of aquatic macrophytes, such as seagrasses and marsh plants. A layer of sediment on top of seeds shields them and emerging seedlings (Marion and Orth , Zhu et al ) from dislodgment by hydrodynamic forces and sediment erosion (Bouma et al , Balke et al , Infantes et al ). In addition, seed burial is crucial for long‐term population and community dynamics by fostering the formation of a persistent soil seed bank (Bakker et al , Thompson ).…”

“…In such systems, seedling recruitment of marine macrophytes (e.g. pioneer marsh plants and seagrasses) mainly takes place in the pioneer zone on the higher tidal flats (Marion and Orth , Zhu et al ), where sediment dynamics (e.g. erosion and accretion) is governed by hydrodynamics and sediment transport, tightly coupled with the engineering activities of benthic animals (Herman et al , Widdows and Brinsley ).…”