Impacts of coastal realignment on biodiversity. A systematic review and meta-analysis

In the context of climate change and sea-level rise, several types of management are employed, including coastal realignment, which consists in reopening polders to marine intrusions. This intervention induces changes in biodiversity. A systematic review, including a meta-analysis, was carried out to assess the impact of coastal realignment on biodiversity. 4 476 references of published and gray literature were collected from two publication databases, Google Scholar and specialist websites. After a screening process, a database of 255 relevant articles corresponding to 866 studies (one taxon in one site) was constructed. Qualitative data were extracted in order to identify knowledge gaps and clusters. Focusing on the 190 studies with a Before-After-Reference-Intervention experimental design, the risk of bias in studies was assessed. Excluding studies with a high level of bias or with non-extractable data, quantitative data related to abundance and species richness were analyzed from 19 and 24 studies respectively. Study sites are mostly in the USA and the UK, but also in Canada and other European countries. Plants are the main group of taxa studied while mammals, amphibians and reptiles are rarely considered. Similarly, studies focus mainly on species richness and abundance but much less on structural and functional parameters. The species richness of invertebrates and the abundance of fishes and shorebirds seem to increase after realignment, whereas the species richness of plants decreases. No changes in the species richness of birds, fishes and macrocrustaceans, and in the abundance of birds, invertebrates, macrocrustaceans and plants, were found. More research on lesser studied taxa and parameters is encouraged to obtain a broad view on the subject and help with decision-making in coastal-realignment operations by providing them with comprehensive ecological arguments. In order to enhance the reliability and reusability of research in other synthesis projects, it is important that data reporting be improved.