From Detection to Legal Knowledge: Environmental DNA Monitoring, Epistemic Due Diligence, and the Future of Marine Biodiversity Governance

International marine environmental law increasingly depends on scientific information, but the legal consequences of new monitoring technologies remain underexplored. This article asks when environmental DNA (eDNA) monitoring may affect what states knew or ought reasonably to have known about marine biodiversity risks and consequently the application of due-diligence obligations. Drawing on Articles 192, 194, and 204–206 of the United Nations Convention on the Law of the Sea (UNCLOS), relevant jurisprudence of the International Court of Justice (ICJ) and the International Tribunal for the Law of the Sea (ITLOS), and the agreement under the UNCLOS on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (BBNJ agreement), it uses “epistemic due diligence” as an analytical label for the informational dimension of existing duties of prevention, vigilance, monitoring, and assessment rather than as a new freestanding obligation. The article argues that scientific maturity, accessibility, and standardization can alter the factual baseline against which constructive knowledge and methodological adequacy are assessed. The analysis focuses primarily on water-derived (aqueous) eDNA, for which marine monitoring practices and standardization are most developed. Sediment-derived eDNA is considered a distinct matrix whose greater persistence and temporal integration require separate interpretive caution. eDNA monitoring results cannot constitute automatic legal knowledge because transport, degradation, contamination, sampling design, and reference-database limitations constrain inference. To discipline this assessment, the article proposes a five-factor eDNA knowledge test based on reasonable detectability, scientific maturity, accessibility and capacity, environmental gravity, and corroboration, organized in two stages: adequacy of the monitoring method and evidentiary evaluation/institutional response. The framework identifies the legally defensible space between environmental ignorance and what states ought reasonably to know.