In order to evaluate recent nature development measures, ground beetles and spiders were studied in the river IJzer estuary (Belgium), an area that has been studied for these invertebrates without interruption since 1989. Starting immediately after restoration measures, five intensive short-term pitfall trapping campaigns were performed in 2001 till 2003 along nine transects covering the entire nature reserve. About 25.000 ground beetles and spiders were identified from more than 200 species. Assemblages, derived from these sampling campaigns, are compared between old and new habitats and sites and show quick species responses in the first years after the nature restoration measures. We observe several beetles and spiders new to the study area as well as a marked increase within the area of several target species with high conservation interest (Red data book species). However, beetle and spider results also suggest that additional management measures will probably be necessary for a further successful development of the nature restoration area. These mainly concern problems related to the maintenance of early successional dynamic stages of great biological value as well as those related to recently observed increased sand deposits in new and old salt marshes. Further invertebrate monitoring, including population genetics, therefore is a pre-requisite for a well-founded long-term evaluation of the performed nature development measures. Such monitoring will be of much interest, both for an evidence based nature conservation management and for fundamental ecological research.