There is accelerating momentum and opportunity for designating very large marine protected areas. A very large percentage of MPAs are tiny - nearly 50% are smaller than 10 sq km. Both small and large MPAs can export adult or larvae marine species and be useful for human fisheries (by supplementing populations in surrounding areas), but MPAs are less useful for biodiversity if the animals they export suffer significant fishing mortality. MPAs that can reduce mortality and protect critical life history phases where they occur are much more effective than those that do not.
Research suggests large MPAs are much more cost-effective to implement and manage compared to smaller MPAs (McCrea-Stroub et al 2010), and in general larger areas will provide better protection from activities that occur outside the MPA. However, it is important to note that small and well managed MPAs can still achieve important conservation benefits. A growing number of large MPAs cover the oceans of many countries and high seas areas protecting diverse pelagic ecosystems, offshore seamounts, and ocean trenches, including the recently designated St Helena Marine Protected Zone in the UK and Rapa Nui Rahui Marine Protected Area.
BOLD - designated and implemented
* Officially designated, but not yet implemented
**Establishment of the MPA was ruled illegal by a UN tribunal in March 2015. Status uncertain.