The exchange of larvae and adult organisms among MPAs is the fundamental biological rationale for MPA networks. To function as an effective network, the MPAs should be spaced to facilitate the connectivity between one another. Spacing of individual MPAs within the network is critical to maximize recruitment outside the MPAs. The design of the network of MPAs should: (1) accommodate the long distance dispersal of larvae; (2) capture the biogeographic range of variation in habitats and species.
Spacing and Larval Dispersal
Movement out of, into and between MPAs by adults, juveniles, larvae, eggs, or spores of marine organisms depends on their dispersal distance, and guides spacing aspects of MPA network design. In general, the lower the effective larval dispersal of a species, the closer the MPAs will have to be to provide benefits to unprotected areas. MPAs that are more closely spaced are more likely to be ecologically connected and serve to protect a greater number of species through movement of young and increased recruitment from other MPAs. Therefore, MPAs should be spaced appropriately to capture the broadest range of dispersal distances as possible.
Spacing and Habitat
MPA spacing is habitat dependent. Habitat distribution patterns should influence where the MPAs are placed and how they are spaced. Within an MPA network, what matters is not spacing to the next MPA, but spacing to the next MPA that offers suitable habitat for the target species (or range of target species). Based on the habitat distribution or larval dispersal of the target species, spacing between MPAs can be established.
In general, the following spacing guidelines are recommended:
- To facilitate dispersal and promote connectivity between MPAs, MPAs should be placed appropriately to capture the middle range of dispersal distances. It is recommended that MPAs should be placed within 10 - 20 km of one another to capture effective connectivity.
- MPAs should be spaced to capture the biogeographic range of variation in habitat and species.
- Variable spacing is better than fixed spacing when there are several small reserves rather than a few large reserves (as long as they are within this 10-20km range).1,2