Impact of an invasive plant (Elymus athericus) on the conservation value of tidal salt marshes in western France and implications for management: Responses of spider populations

The species composition, functional groups, abundances and densities of spider assemblages were also compared using complementary sampling techniques (i.e., pitfall traps, collecting by hand and quadrat technique) between natural and invaded stations in 2002 for synchronic approach. One main result is that some halophilic species decreased in abundances and densities in invaded plots, which is thought to alter the marine character of salt marsh arthropod assemblages. Lastly, mowing, by reducing non-coastal species and enhancing halophilic ones, tends to reduce the negative effects of Elymus on salt marsh conservation value. The relation between the treatments tested (invasive species and mowing) and the spider assemblages by changes in environmental variables confirms the high value of this group as bioindicators.