This deliverable maps the European aquatic eDNA “digital ecosystem” – the connected (and often disconnected) set of repositories, standards, taxonomies, and web services that underpin routine, comparable, and reusable eDNA-based biodiversity monitoring. It complements D3.1 (curated reference libraries) and D3.2 (metadata standards for eDNA repositories) by focusing specifically on connectivity (linking) and interoperability (compatibility) across infrastructures, and by highlighting the gaps that impede end‑to‑end traceability from biodiversity observations back to sequences and physical samples.