Stepping Stones Along Urban Coastlines—Improving Habitat Connectivity for Aquatic Fauna with Constructed Floating Wetlands

Urban development along coastlines is accompanied by habitat fragmentation and loss of habitat connectivity, particularly affecting the habitat and nursery function of estuarine areas for migratory marine species. Constructed floating wetlands, deployed as ‘stepping stones’ along urban coastlines where natural wetlands are missing, offer the potential to partially replace lost ecosystem services. Originally developed for wastewater treatment, constructed floating wetlands are now used to improve landscape aesthetics or create habitats for aquatic fauna and birds. This study presents a toolkit to identify appropriate sites for stepping stones using open source data and open source software alone. The toolkit was used to identify 85 potential installation sites along the German Baltic Sea coast, a large proportion of which are located in protected areas offering synergies with nature conservation measures. Though the sites are often located in protected areas, the field investigation revealed that natural vegetation is largely absent from the estuaries near urban areas. Constructed floating wetlands can never replace ‘core areas’ in ecological networks, but they can serve as stepping stones improving habitat connectivity, especially for diadromous fish species such as the threatened European eel. To ensure not only structural connectivity, but also functional connectivity, restoration efforts at the land-sea interface must be holistic and include adequate hydrologic connectivity.