Coral Reefs: A Reef Resilience Toolkit Module

Shape Matters

There are two components of shape to consider in the design of an MPA:

The shape of an MPA is a critical factor in effetive delineation and enforcement. MPAs with regular shapes, like the MPA example on the left, can be delineated by lines of latitude and longitude and are more easily enfoceable. MPAs of irregular shapes, like that on the right, are not easily identifiable or enforced and should be avoided. Images courtesy The Nature Conservancy

1. Shape and edge effects
2. Enforceability of regularly shaped boundaries with clear landmarks or coordinates

Shape and Edge Effects

In the design of an MPA, it is important to consider the ratio of edge habitat versus core interior habitat, as the edges (or perimeter boundary line) of MPAs are often extensively fished, and therefore do not offer the same refuge to fish species as the interior protected areas do. Juvenile and adult spillover from the MPA is edge-dependent, and as the amount of edge of an MPA increases, faster export is expected, relative to the total protected area.

• When designing shape for biodiversity conservation, it is important to minimize edge habitat and maximize interior protected area.
• When designing shape for fisheries management, it is important to consider the type and spatial extent of the habitat bordering the reserve, since this will influence emigration (i.e. continuous habitat inside and outside the reserve will enhance the effects of spillover, or export of fish).

Shape and Enforceability

The shape of an MPA is also a critical factor in effective delineation and enforcement. A shape that allows for clear marking of boundaries for both resource users and enforcement personnel may increase effectiveness. MPAs with boundaries that conform to natural habitat edges offer fuller protection than MPAs with boundaries that cross reef habitat types and zones. However, the ease of compliance and enforcement capabilities need to be taken into account.

• MPAs should be contiguous, compact and easily delineated.
• Consider obvious, easy GPS reference points, such as landmarks and distinct habitat types.
• Regular MPA shapes of squares or rectangles are preferable because they can be delineated by lines of latitude and longitude, and therefore more easily identified by user groups.