In the wake of the designation of two new ‘marine protected areas’ adjacent to the coastal waters of the South Orkney Islands (British Antarctic Territory) and the Chagos Archipelago (British Indian Ocean Territory), this commentary considers some of the geographical, legal and political implications of these unilateral declarations – taking into account competing claims of jurisdiction by Mauritius and the Maldives, human rights claims of the Chagos islanders, strategic interests of the United States in the Indian Ocean, and shared legislative competences of the European Union in the field of marine fisheries. The two case studies also raise questions of global arms control, diplomatic efforts at ‘greening’ imperialism, and contemporary state practice with regard to the ‘sacred trust of civilisation’ for dependent territories, as spelled out in the United Nations Charter.