<p>The Agreement on the Conservation and Sustainable Use of Marine Biological Diversity of Areas Beyond National Jurisdiction (BBNJ Agreement) marks a significant milestone in global ocean governance, aiming to coordinate the diverse institutions involved in marine biodiversity governance. However, little is known about the structure of maritime biodiversity regime complex – does it remain fragmented, or has it already developed forms of coordination over time? This study extends the concept of institutional deference to analyze the structural features of the existing marine biodiversity regime complex and assess the implications for the BBNJ Agreement as it enters this institutional landscape. Drawing on nearly 2,000 official documents from 32 international organizations (IOs) spanning four decades, we map institutional deference patterns using social network analysis to reveal the structure of the marine biodiversity regime complex. We find a polycentric but coordinated architecture, with global institutions such as FAO, IMO, and UNCLOS functioning as central hubs. This structure suggests that effective governance can emerge without a single overarching authority, relying instead on coordination among differentiated institutions. We propose that international ocean management is best advanced through mini-lateral mechanisms linking key “boundary centers” rather than through a comprehensive meta-organization. Furthermore, adaptive management depends on dynamically identifying institutional stakeholders through observed deference patterns, rather than formal hierarchies. This study offers a new lens to understand how the BBNJ Agreement might foster resilient and responsive governance in areas beyond national jurisdiction in the future.</p>