Evaluating the success of managed realignment for the restoration of salt marshes: Lessons from invertebrate communities

Studying successional processes and related factors in salt marshes encompasses both fundamental (community structuration) and applied (biodiversity conservation and restoration) issues. Current managed realignment projects and sites where, in the past, large storm events led to breaches in embankments create unique experimental conditions for such challenges by re-instating tidal inundation and salt-marsh development. We conducted a pair-matched approach using natural and recreated (either accidentally or managed) salt marshes and studied changes in invertebrate communities over time during a field experiment (Essex, UK). Trophic guild was assigned to all invertebrates, and detailed analyzes conducted on most abundant (amphipods, Orchestia sp., 9666 individuals) and diversified (spiders, 43 species) groups. A total of 27,180 invertebrates (almost all arthropods: 99% of specimens) was collected in 2005. The conservation equivalency was achieved quickly (which was shown here with spider assemblages), but that did not translate into a complete functional equivalency. Indeed neither the structure of trophic guilds, nor the potential role of marine enrichment and fish nursery, estimated through the population size of amphipods, was achieved by managed realignments. We finally argue that the study of invertebrates brings information complementary to those brought by plants, and underline that functional and conservation equivalency have to be assessed separately.