Effects of shoot stiffness, shoot size and current velocity on scouring sediment from around seedlings and propagules

Successful management and restoration of coastal vegetation requires a quantitative process-based understanding of thresholds hampering (re-)establishment of pioneer vegetation. We expected scouring to be important in explaining the disappearance of seedlings and/or small propag- ules of intertidal plant species, and therefore quantified the dependence of scouring on plant traits (flexibility, size) and physical forcing by current velocity. Flume studies with unidirectional flow revealed that scouring around seedlings increased exponentially with current velocity and according to a power relationship with plant size. Basal stem diameter rather than shoot length controlled scour- ing volume. Flexible shoots caused far less scouring than stiff shoots, provided that the bending occurred near the sediment surface as was the case for Zostera, and not on top of a solid tussock base as we observed for Puccinellia. Therefore, shoot stiffness is likely to strongly affect the chances for initial establishment in hydrodynamically exposed areas. Plant traits such as shoot stiffness are sub- ject to a trade-off between advantages and disadvantages, the outcome of which depends on the physical settings.

[1]  Peter M. J. Herman,et al.  Spatial patterns, rates and mechanisms of saltmarsh cycles (Westerschelde, the Netherlands) , 2008 .

[2]  H. Lenihan,et al.  Depletion, Degradation, and Recovery Potential of Estuaries and Coastal Seas , 2006, Science.

[3]  J. Bakker,et al.  Restoration of salt marshes in the Netherlands , 2002, Hydrobiologia.

[4]  Johan van de Koppel,et al.  Does scale‐dependent feedback explain spatial complexity in salt‐marsh ecosystems? , 2008 .

[5]  C. Duarte,et al.  The impact of sediment burial and erosion on seagrasses : A review , 2008 .

[6]  Peter M. J. Herman,et al.  Density-dependent linkage of scale-dependent feedbacks: a flume study on the intertidal macrophyte Spartina anglica , 2009 .

[7]  J. Bruno,et al.  FACILITATION OF COBBLE BEACH PLANT COMMUNITIES THROUGH HABITAT MODIFICATION BY SPARTINA ALTERNIFLORA , 2000 .

[8]  S. Rood,et al.  Effective disturbance: Seedling safe sites and patch recruitment of riparian cottonwoods after a major flood of a mountain river , 2006, Wetlands.

[9]  Bradley D. Robbins,et al.  Desiccation is a limiting factor for eelgrass (Zostera marina L.) distribution in the intertidal zone of a northeastern Pacific (USA) estuary , 2005 .

[10]  C. Clark,et al.  Are Plant Populations Seed Limited? A Critique and Meta‐Analysis of Seed Addition Experiments , 2007, The American Naturalist.

[11]  D. J. de Jong,et al.  Restoration of salt marshes in the Netherlands , 2002 .

[12]  M. M. Katwijk,et al.  Effects of locally varying exposure, sediment type and low-tide water cover on Zostera marina recruitment from seed , 2004 .

[13]  E. Houwing.  Morphodynamic development of intertidal mudflats: consequences for the extension of the pioneer zone , 2000 .

[14]  L. Hanssen,et al.  Guidelines for seagrass restoration: importance of habitat selection and donor population, spreading of risks, and ecosystem engineering effects. , 2009, Marine pollution bulletin.

[15]  B. V. Wesenbeeck.  Thresholds and shifts: consequences of habitat modification in salt-marsh pioneer zones , 2007 .

[16]  P. Rothery,et al.  Monitoring the development of intertidal habitats on former agricultural land after the managed realignment of coastal defences at Tollesbury, Essex, UK. , 2006, Marine pollution bulletin.

[17]  M. M. Katwijk,et al.  Planting density, hydrodynamic exposure and mussel beds affect survival of transplanted intertidal eelgrass , 2007 .

[18]  P. Herman,et al.  Trade-offs related to ecosystem engineering: A case study on stiffness of emerging macrophytes , 2005 .

[19]  Frederick T. Short,et al.  A Global Crisis for Seagrass Ecosystems , 2006 .

[20]  Tjeerd J. Bouma,et al.  Positive Feedbacks in Seagrass Ecosystems: Implications for Success in Conservation and Restoration , 2007, Ecosystems.

[21]  S. Carpenter,et al.  Catastrophic shifts in ecosystems , 2001, Nature.

[22]  Carrie V. Kappel,et al.  Coastal Ecosystem-Based Management with Nonlinear Ecological Functions and Values , 2008, Science.

[23]  S. Bell,et al.  Influence of physical setting on seagrass landscapes near Beaufort, North Carolina, USA , 1998 .

[24]  S. Bell,et al.  DYNAMICS OF A SUBTIDAL SEAGRASS LANDSCAPE: SEASONAL AND ANNUAL CHANGE IN RELATION TO WATER DEPTH , 2000 .

[25]  T. Rand.  Seed dispersal, habitat suitability and the distribution of halophytes across a salt marsh tidal gradient , 2000 .