Ecological consequences of breakwater and revetment structures on the Baltic Sea Coast in Germany

Abstract

Hard structures, such as breakwaters and revetments, while effective at mitigating coastal erosion, induce significant ecological alterations in terrestrial and aquatic environments. To study these effects, field investigations were performed along the Baltic Sea coast in Thiessow, Germany, highlighting breakwaters, a revetment and comparing them to an unprotected area. For this purpose, floristic mappings were carried out along transects on beach and dune. Algae scratch samples and sediment cores were taken, which were also used for nutrient analyses, each with a replicate number of n = 5. Sediment analysis revealed changes in grain size, sorting, water content, organic matter, and nutrient concentrations in areas influenced by breakwaters and revetments. These differences are less distinct on beach and dune. Finer sediments and increased organic content were observed in shallow waters near the breakwaters, while coarser sediments dominated near revetments. Vegetation surveys showed less dune plant species on the breakwater site and a pronounced shift towards ruderal plant species. Revetments eliminated terrestrial vegetation entirely due to their impermeable structure directly on the beach. The introduction of hard substrate in soft-bottom habitats in the shallow water favours the settlement of macroalgae, whereby there is only a weak zonation with regard to the distribution of species on the structures. Meanwhile, no seagrass meadows were recorded near the breakwater which could indicate supressing effects. These findings underscore the ecological consequences of hard coastal protection and emphasize the importance of integrating ecological considerations into coastal protection strategies to balance shoreline stabilization and preservation of natural habitats.