An empirical evaluation of the quality of salt marshes for nekton in the Wadden Sea habitat mosaic

Abstract

In the Wadden Sea, a shallow coastline and a large tidal amplitude result in an overlap of land and sea, creating a unique pulsing ecosystem. The landward edge of this intertidal area is framed by salt marshes, that evolve, where low flow velocities allow for sediment accretion and settlement of halophytic plants. Salt marshes are valued worldwide as high-quality habitats for fish and crustaceans, because they provide shelter from predators and profitable feeding conditions. In the Wadden Sea, however, land reclamation, coastal protection measures, and agriculture have changed shape and function of salt marshes over centuries. Naturally meandering salt-marsh creeks connecting i. a. intertidal pools were largely replaced with short and straight creeks to ensure optimal dike drainage. Whether these mostly artificially created salt marshes can still support marine fauna and which species enter the confined salt-marsh creeks, hazarding beaching and unfavourable temperatures, was mostly unknown and is now addressed by this thesis. For the Wadden Sea area, it is the first comprehensive study showing which nekton species are characteristic for marine Wadden Sea salt marshes, evaluating habitat quality based on abiotic conditions, predation pressure, food availability and the body condition of fish, and examining the human impact on this habitat type, particularly sheep grazing.