Can Widely Used Methods Be Turned Into <scp>eDNA</scp> Samplers for Ground‐Dwelling Arthropods? Insights From Two Pilot Studies in West European Salt Marshes

ABSTRACT The pressing demand for arthropod preservation, coupled with a decline in taxonomic expertise and available resources, calls for innovative strategies in assessing biodiversity. Metabarcoding and more recently environmental DNA (eDNA) metabarcoding have been shown to be a promising technique for identifying terrestrial arthropods. This research evaluated the efficacy of two conventional sampling approaches, adapted for metabarcoding surveys, in monitoring the diversity of spiders (Araneae) and beetles (Coleoptera) within salt marsh environments. The methods tested were suction sampling (G‐vac) and modified pitfall traps (NDC, a non‐destructive DNA collector). Through two pilot experiments in salt‐marsh environments, we found that both methods successfully identified diverse arthropod communities, though discrepancies with traditional morphological identification highlighted the strengths and limitations of molecular approaches. Suction sampling excelled in detecting taxa such as Lepidoptera and Salticidae, which are often overlooked by physical collections, whereas modified pitfall traps performed well for dung beetles but faced challenges with wolf spiders (Lycosidae). Our findings underscore the importance of tailoring eDNA protocols to specific taxonomic groups and ecosystems, particularly through strategic primer and DNA fragment selection. While traditional methods remain indispensable for comprehensive biodiversity inventories, eDNA metabarcoding offers a powerful complementary approach for detecting cryptic or undersampled taxa. This study emphasizes the need for the targeted adaptation of eDNA techniques to specific taxonomic groups and ecosystems. Primer choice and DNA fragment selection significantly influenced detection efficiency, with broader primers reducing taxonomic resolution and amplifying bias. Although traditional methods remain critical for comprehensive biodiversity inventories, bulk and eDNA metabarcoding offer a complementary tool. These findings contribute to advancing arthropod monitoring tools and aiding conservation efforts amidst declining entomological resources.