Navigating Sovereignty and Marine Biosecurity: The Challenge of Regulating Visiting Naval Vessels in Global Ports

Environmental security has traditionally focused on climate change, resource scarcity and environmental degradation as drivers of instability and conflict. Comparatively little attention has been given to environmental biosecurity despite biological invasions representing one of the most significant and irreversible forms of environmental change affecting both terrestrial and aquatic ecosystems worldwide. In the marine sphere, international governance has responded to biosecurity risks associated with commercial shipping through progressively stronger regulation of ballast water and vessel biofouling. However, sovereign naval vessels remain largely outside these regulatory frameworks because of the long‐established principle of sovereign immunity. Although sovereign immunity remains fundamental to international law and the effective conduct of defence operations, it has unintentionally created an institutional blind spot where environmental risks generated by military mobility receive limited oversight. Using AUKUS as a contemporary case study, this article argues that marine biosecurity represents an overlooked dimension of environmental security whose governance currently falls between environmental law and defence policy. The article demonstrates how sovereign immunity contributes to institutional fragmentation and proposes policy mechanisms capable of integrating environmental stewardship into defence cooperation while preserving legitimate security interests.