European scale salt-marsh responses to climate change and sea level rise

Salt-marshes are regarded as valuable coastal ecosystems, which not only serve as important habitat for e.g. birds and (spawning) fish, but also can fulfill an important role in coastal protection. Therefore, it is important to understand how salt-marshes will respond to changing conditions due to anthropogenic pressure, climate change and sea level rise. What are the limits within the coastal vegetation to cope and adapt to these fast increasing pressures? Theseus offered the unique opportunity to test such ideas about salt-marsh responses on a European scale.

The NIOO-KNAW / NIOZ* in Yerseke (Netherlands) is currently coordinating ecologists from the UK (Bangor and Plymouth), Spain (Santander), and Italy (Ravenna) that are participating in a large scale study. Two simple but highly informative experiments are being replicated across Europe. The first experiment looks at the growth rates of important salt-marsh pioneer species under different inundation regimes. To do so, a vertical garden or “marsh-organ”, is erected in the marsh. On this structure, pots with marsh-plants hang on different heights thereby mimicking differences in inundation. This experiment will give insight in how changes in inundation, e.g. due to sea level rise, will change the ability of vegetation to grow across Europe, accounting for differences in tidal amplitudes. The second experiment aims to unravel the most important processes that limit establishment of vegetation on mudflats. To this end, the survival of seedlings transplanted along mudflats will be tracked. This experiment is expected to reveal how regional climate and tidal regime are determining the vulnerability of salt-marsh vegetation to environmental changes. The knowledge gained opens possibilities to assess current salt-marsh ‘health’ and estimate future marsh development. Moreover, it will give insight in which locations are suitable for development of salt-marshes as soft mitigation option, and which environmental conditions need some engineering in order to locally stimulate marsh development.

A marsh-organ in the Oyambre estuary near Santander (Spain).