The optimal size of a coral reef MPA is designed around a strictly protected zone or core, or a collection of such zones, each of which encompasses sufficient target coral area to be self-replenishing for all species.

• This focus on replenishment is particularly important when preserving biological diversity is the principal management objective. It may seem less important for other objectives, such as maintaining the area's value for recreation, tourism, research, education, and spawning of specific fishes.

• However, coral bleaching has shown us that replenishment is an equally important consideration for reef survival, regardless of the management objective. Bleaching events cannot be hindered by MPA zones, boundaries, regulations, or management efforts unless these are designed specifically to meet the requirements for reef survival.

Determining the critical minimum size at which coral reef communities may be self-replenishing is still very imprecise science. However, the following guidelines are strongly recommended:

• A core area of about 450 ha should be designated until studies indicate otherwise.

• The core should be selected so that it encompasses as diverse as possible a range of reef habitats.

• A single reef is preferable, but a cluster of small reefs will probably be equally effective when these are managed as an integrated unit.

The design team should choose carefully from the many objectives for protecting coral reefs. Among others, these include providing for recreational activities, contributing to fisheries, preserving biological diversity, protecting endangered species or the breeding stock of other valuable species.

• Primary importance should be given to resilience and the subsidiary objectives involved in protecting reefs for resilience.

• Objectives are the basis of design, so take care to define and obtain wide consensus on these and to include resilience among them.