Crises such as water quality, pollution, climate change, overfishing, biodiversity, energy, waste, and carbon sequestration mean that legislation protecting the marine environment is under intense pressure to be effective and to demonstrate positive results in a vast array of public and private spheres. Thus far, scholarship of EU marine environmental law has been focused primarily on (i) interaction with international agreements (ii) spatial/jurisdictional studies (iii) analysis of new laws, plans and programmes (iv) principles (e.g. good environmental status, precautionary approach, polluter pays) (v) CJEU case analysis (vi) enforcement (vii) specific issues (plastics, litter…). However, over the years the mass constituted by the EU marine environment acquis has grown ever-larger, leading to risks of poor coordination, over-regulation in some areas and lack of regulation in others. By triangulating complementary investigatory methodologies, this study teases out systemic, diachronic and legilinguistic interlinkages—within and across key instruments as well as EU institutions, bodies and agencies. Our results provide avenues for policymakers nationally and at EU level to improve the legibility and coherence of marine environmental regulation—to the benefit of citizens and the wider body of stakeholders, and, ultimately, to benefit the marine world.