Large, regional-scale marine protected areas (MPAs) and MPA networks face different challenges in governance systems than locally managed or community-basedMPAs. An emerging theme in large-scaleMPA management is the prevalence of governance structures that rely on institutional collaboration, presenting new challenges as agencies with differing mandates and cultures work together to implement ecosystem-based management.

We analyzed qualitative interview data to investigate multi-level social interactions and institutional responses to the surprise establishment of the Papah¯anaumoku¯akea Marine National Monument (monument) in the northwestern Hawaiian Islands (NWHI).

The governance arrangement for the monument represents a new model in US MPA management, requiring two federal agencies and the State of Hawai‘i to collaboratively manage the NWHI.

We elucidate the principal barriers to institutional cotrusteeship, characterize institutional transformations that have occurred among the partner agencies in the transition to collaborative management, and evaluate the governance arrangement for the monument as a model for MPAs.

The lessons learned from the NWHI governance arrangement are critical as large-scale MPAs requiring multiple-agency management become a prevalent feature on the global seascape.