Multiple Environmental Variables Affect Germination and Mortality of an Annual Salt Marsh Pioneer: Salicornia procumbens
Regteren, M. Van; Meesters, E.H. ; Baptist, M.J. ; Groot, A.V. De; Bouma, T.J. ; Elschot, K. - \ 2020
Estuaries and coasts 43 (2020). - ISSN 1559-2723 - p. 1489 - 1501.
Salt marsh - Annual - sediment dynamics - intertidal flat - Inundation regime - seedling recruitment
Salt marshes, providing numerous ecosystem services, are degrading worldwide. To effectively aid conservation and restoration efforts, increased knowledge on marsh expansion processes and the initial establishment of pioneer vegetation is essential. In this study, we disentangle environmental drivers that affect the lifecycle of the annual pioneer Salicornia procumbens at the salt marsh edge. We studied the effect of various environmental variables on the start of germination, germination success and mortality before seed-set in a field experiment in the DutchWadden Sea atWesthoek. Our results indicate that temperature and sedimentation inhibited the initiation of germination. Once germination occurred, higher precipitation rates increased germination success. In contrast,
sedimentation rates above 0.5 mm day−1 halved germination success through burial of freshly sprouted seedlings. Unexpectedly, natural germination was low, indicating that seed availability may have been limited, despite a seed source nearby. Frequent inundation, extended periods without inundation (through desiccation of the soil) and a highly dynamic bed level increased mortality before
seed-set. Consequently, bed-level dynamics (erosion, sedimentation and bed-level variation) impact seed production dually (decrease germination and increase mortality) and thus potentially reproduction success. A high seed reproduction is crucial for annuals, such as S. procumbens, to re-establish the following year. Next to advancing our general knowledge of natural salt marsh expansion, results in this study can also be used to assess the potential of a given site for saltmarsh stimulation or restoration. Seed availability and local bedlevel dynamics are key in the successful establishment of a salt marsh pioneer: Salicornia procumbens.
The ecosystem engineer Crassostrea gigas affects tidal flat morphology beyond the boundary of their reef structures
Walles, B. ; Salvador de Paiva, J. ; Prooijen, B. van; Ysebaert, T. ; Smaal, A.C. - \ 2015
Estuaries and coasts 38 (2015)3. - ISSN 1559-2723 - p. 941 - 950.
wadden sea - sediment dynamics - pacific oysters - native mussels - habitat - estuary - stabilization - enhancement - communities - adaptation
Ecosystem engineers that inhabit coastal and estuarine environments, such as reef building oysters, do not only stabilise the sediment within their reefs, but their influence might also extend far outside their reefs, affecting tidal flat morphology and protecting the surrounding soft-sediment environment against erosion. However, quantitative information is largely missing, and the spatially extended ecosystem engineering effects on the surrounding soft-sediment largely unstudied. To quantify this, we measured elevations around eleven natural Crassostrea gigas reefs occurring on tidal flats in the Oosterschelde estuary (the Netherlands). These tidal flats experience strong erosion as a consequence of human interventions in the system. Various reef sizes were chosen to test the proportional effects of reefs on tidal flat morphology. Measurements were used to create 3-dimensional surface maps to obtain properties of the reefs and the surrounding soft-sediment environment. The area of the oyster reefs ranged from 2 to 1,908 m2. Reef length varied between 1 and 61 m, reef width between 1 and 45 m, and reef height between 0.20 and 1.08 m. Reefs varied in shape, going from round shape structures to more elongated ones. We observed elevated areas (>5 cm elevation from the background intertidal slope) on the lee side of all reefs, caused by the interaction between the reef’s structure and locally prevailing wave conditions. The elevated area (i.e. the spatially extended ecosystem engineering effect) affected by the reef was of the same order of magnitude as the reef area. The elevated area was related to reef properties such as reef length, width, and height. Reef length, however, appeared to be the best predictor. These findings contribute to management solutions for coastal adaptation and protection. Our study clearly showed that oyster reefs not only protect the tidal flat under their footprint, but as well an area beyond the boundary of the reef