A recent UN study highlights the world should safeguard coral reefs with networks of small no-fishing zones to confront threats such as climate change, and shift from favoring single, big protected areas.
The UN University Institute for Water, Environment and Health describe how smaller effective networks of MPAs may be more effective in conservation than large areas - the dominant approach.
Fish and larvae of marine creatures can swim or be carried large distances, even from large protected areas. It is often best to set up a network of small no-fishing zones covering the most vulnerable reefs (or other important habitats or breeding grounds) with catches allowed in between. Closing big zones can be excessive for conservation and alienate fishermen who then ignore bans.
While the research relates to reefs, the lessons are clear irrespective of the habitat to be protected. We must take an ecosystems approach to protection of marine habitats, that takes into account the ecology of the features under protection, and critically, the activities of humans in the system.