Seed arrival and persistence at the tidal mudflat: identifying key processes for pioneer seedling establishment in salt marshes

Abstract

Salt marshes are highly valuable ecosystems that provide numerous important ecosystem services. Given the global marsh decline, there is a pressing need to understand the natural bottlenecks and thresholds to their establishment and long-term ecological maintenance. Seed presence in the right place and time is a prerequisite for pioneer establishment. We performed field surveys and manipulative seed-bank experiments on 2 mudflats with different levels of exposure in the Westerschelde, The Netherlands, to identify patterns of seed arrival and persistence and their role in determining seed bank abundance. Seed arrival decreased with distance from the seed-source area, i.e. the salt marsh, resulting in seeds being deposited on the mudflat close to the marsh edge. Once arrived, most of the surface seeds were washed away during subsequent tides, with retention of < 20%. However, seed burial enhanced seed retention nonlinearly with increasing burial depth. Predation was not a major cause of seed loss. These results point to the importance of hydro dynamic and morphodynamic processes to both lateral seed dispersal and vertical seed burial on tidal flats and, therefore, suggest that saltmarsh establishment and expansion are closely linked to the physical dynamics of the entire estuarine system.

Limited seed retention during winter inhibits vegetation establishment in spring, affecting lateral marsh expansion capacity

“…Once dispersed to a suitable habitat, seed retention is affected by environmental variables which ultimately control successful plant establishment. Factors shown to influence seed retention and the local seed bank are sedimentation (Balke et al, ) and erosion rates (Houwing, ; Zhu, Bouma, Ysebaert, Zhang, & Herman, ), topographic heterogeneity (Chang et al, ), and bioturbating infauna (Delefosse & Kristensen, ). The burial of seeds, through sedimentation or bioturbation, can increase seed retention, as they are protected against erosive forces under a layer of sediment (Zhu et al, ).…”

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 ).…”

Sprouting as a gardening strategy to obtain superior supplementary food: evidence from a seed‐caching marine worm

“…Consequently, burial does not necessarily end up with all sprouts being consumed and may incidentally result in directed dispersal, which can increase seed persistence by decreasing seed removal caused by the tide (Zhu et al. ).…”

“…They have been shown to deliberately bury cordgrass seeds into their burrows, thereby reducing seed loss to hydrodynamic processes (Marion and Orth , Zhu et al. ). While ragworms were thought to be seed predators (Emmerson , Paramor and Hughes ), the direct consumption of intact cordgrass seeds had never been observed.…”