The anthropogenic impact on the worlds ecosystems is severe and the need for non-invasive, cost-effective tools for monitoring and understanding those impacts are therefore urgent. Here we combine two such methods in a comprehensive multi-year study; camera trapping (CT) and analysis of environmental DNA (eDNA), in river marginal zones of a temperate, wetland Nature Park in Denmark. CT was performed from 2015 to 2019 for a total of 8,778 camera trap days and yielded 24,376 animal observations. The CT observations covered 87 taxa, of which 78 were identified to species level, and 73 were wild native species. For eDNA metabarcoding, a total of 114 freshwater samples were collected from eight sites in all four seasons from 2017 to 2018. The eDNA results yielded a total detection of 80 taxa, of which 74 were identified to species level, and 65 were wild native species. While the number of taxa detected with the two methods were comparable, the species overlap was only 20 %. In combination, CT and eDNA monitoring thus yielded a total of 115 wild species (20 fishes, four amphibians, one snake, 23 mammals and 67 birds), representing half of the species found via conventional surveys over the last ca. 20 years (83% of fishes, 68 % of mammals, 67 % of amphibians, 41 % of birds and 20 % of reptiles). Our study demonstrates that a holistic approach combining two non-invasive methods, CT and eDNA metabarcoding, has great potential as a cost-effective biomonitoring tool for vertebrates.

1. The longstanding debate in conservation biology on the importance of single large or several small (SLOSS) habitats for preserving biodiversity remains highly relevant, given the ongoing degradation and loss of natural habitats world-wide.Restoration efforts are often constrained by limited resources, and insights from SLOSS studies therefore have important implications if restoration efforts can be optimized by manipulating the spatial configuration of restored habitats. Yet, the relevance of SLOSS for habitat restoration remains largely unexplored.2. Here, we report the effects of spatial reef configuration on early colonization of marine organisms after restoring boulder reef habitats. Reefs were restored in single large (SL) and several small (SS) designs in the western Baltic Sea, where century-long boulder extraction has severely degraded large reef areas and likely exacerbated regional declines in commercially important gadoids (Gadidae spp.).We sampled the field sites using remote underwater video systems in a beforeafter control-impact (BACI) design and obtained probabilistic inferences on restoration and SLOSS effects from Bayesian hierarchical models.3. Probabilities of a positive restoration effect were high (>95%) for gadoids, labrids and demersal gobies, moderate (60%-75%) for species richness and sand gobies, and low (<5%) for flatfish abundance. Notably, gadoid abundance increased 60-fold and 129-fold on average at SL and SS respectively. The species composition at restored reefs deviated from control sites, mainly driven by large-bodied piscivores.4. Spatial reef configuration had the strongest effect on small-bodied mesopredators, including gobies, which were more abundant at SS and driving distinct species assemblages between the reef designs. In addition to providing suitable conditions for reef species, results suggest that SS can also benefit soft-bottom taxa, possibly through a dispersed predator-mediated effect relative to SL. Synthesis and applications.This study demonstrates that boulder reef restoration can strongly promote the abundance of exploited gadoids (e.g. Atlantic cod) and is therefore a promising management tool to support top-down controls by | 2937