Why Include Replicate Habitat Types within MPAs?

Replication of habitat types within MPAs within a network is important for several reasons:

To provide a stepping-stone for the dispersal of marine species
To insure against catastrophic local disasters that can significantly impact an individual, small MPA
For use as reference sites during monitoring and to evaluate the effects of human influences on communities

Replication is the inclusion of multiple samples of habitat types in MPAs and networks to spread the risk of large-scale events, such as bleaching. Replication of protected resistant and resilient coral communities at multiple sites increases the probability that some reefs will survive bleaching, and helps the recovery of affected areas.

MPA networks are most effective when each habitat type is represented in more than one MPA. The goal of representation could be met by having only one MPA for each biodiversity element; however, if the habitat is destroyed in the one MPA, representation of that diversity would be compromised, as there would be nothing under protection. Replication provides a buffer against catastrophic loss of an MPA.

To spread the risk of damage or extinction by ensuring that habitat types are replicated in the network, the following guidelines are recommended:

California Central Coast MPA design includes several replicate habitats. Click image for larger version. Taken from Guide to the Central California Marine Protected Areas

At the very minimum, three replicates of habitat type should be included, but more is always better. The number of replicates of each habitat type must be a balance between ensuring representation and ensuring effective monitoring and enforcement.
For large biogeographic areas (100s–1000s km), the MPA should conserve a representative example of each bioregion.
For smaller areas (1 km–100s km), the MPA should include reef types and major reef zones, which can serve as proxies (or substitutes) for community types.

Replicate MPA sites enable the dispersal of marine species between areas. Many marine species follow a stepping stone model1, in which populations exchange larvae with adjacent populations. Replicate MPAs can be designed to accommodate dispersal patterns of species, and facilitate connectivity between the sites. Spacing considerations will also influence fulfilling the stepping stone role of MPAs.

Replication of MPAs also provides analytical power for management comparisons. With more than one MPA, reference, or control sites, can be incorporated into the monitoring program to evaluate the biological changes in and between each of the MPAs. This type of comparison facilitates adaptive management.