European intertidal marshes: a review of their habitat functioning and value for aquatic organisms

Salt marshes form true ecotones between land and sea fauna and flora that have adapted to an environment that is both aquatic and terrestrial in nature. Despite the extreme and sharp gradients that exist in salt marshes, they form the temporary or permanent home for many animals and plants and they fulfil many important roles in marine and estuarine ecosystems. While research on the terrestrial component of European marshes has helped in their management, knowledge of the aquatic component has largely been ignored in safeguarding the existence and ecological importance of tidal marshes. This situation is in sharp contrast with studies of coastal marshes along the eastern and southeastern coasts of North America. The typical European salt marsh differs in several physical aspects from the typical American salt marsh, but recent investigations have indicated parallels regarding nekton habitat usage. The present paper reviews the current state of European studies on the habitat role that tidal marshes play for fish and crustacean fauna. Mirrored against the more extensive American literature, we discuss where functional similarities and differences exist between both types of tidal marshes and where further knowledge is still needed for European marshes. Management of European tidal marshes would benefit from extending the current knowledge, and this paper identifies potential topics of interest.