From an ecological perspective, transboundary corridors like MOCOR are far superior to isolated MPAs, Verónica Relaño, a postdoctoral fellow at Spain’s University of Santiago de Compostela whose work focuses on marine protection effectiveness, told Mongabay in an email. Relaño is also the oceans director at the Germany-based NGO Onewater.

“Marine life — especially migratory species, larvae, and pelagic fish — does not adhere to EEZ [Exclusive Economic Zone] boundaries,” Relaño said. “Isolated MPAs often end up functioning as ecological islands and industrial fleets simply wait at the edges to ‘fish the line’. A corridor design connects critical habitats and protects entire migration routes.”

But large-scale designs can make governance challenging, according to Relaño, who codeveloped an index identifying “paper parks” by measuring the gap between a site’s formal protection status and on-the-ground enforcement. Relaño said that while well-protected MPAs can halt extraction and allow depleted populations of fish and other marine species to bounce back to healthy levels, paper parks lacking adequate management and enforcement often permit fishing fleets to continue extraction. Because these ineffective protected areas still count toward global 30×30 targets, nations might prioritize quantity over quality, she said.

“The greatest risk in a corridor design is the ‘weakest link’ scenario. If one country in the network lacks the monitoring or managing capacity or the political drive to enforce its boundaries, illegal and distant-water fleets will concentrate their extraction in that specific zone, undermining the integrity of the entire corridor,” Relaño said.