A protected area is defined by the Convention on Biological Diversity as "a geographically de-fined area, which is designated or regulated and managed to achieve specific conservation objectives".
Protected areas may be marine sanctuaries meant to protect biodiversity while serving other non-conflicting uses, or they may be areas set up to restrict or prohibit a particular activity, such as fishing or ship traffic, because the ecosystem is deemed to be particularly sensitive to that activity. Regulations depend on what are seen as the major threats to biodiversity and what the public will support or tolerate two criteria that may be in conflict with each other.
In multiple-use areas, exploitation of resources may be allowed within sanctuary boundaries; the challenge is to make sure the exploitation is restricted to sustainable levels. Large areas are usually preferable for multiple-use reserves, but their size makes enforcement difficult. Even in those rare areas with total, park-like protection, the effects of visitors must be mini-mised if protection is to work. Multiple-use marine protected areas are often seen as a vehicle for establishing effective integrated and adaptive management programmes.
Large areas are usually preferable for multiple-use reserves, but the large size makes en-forcement difficult. In order to be effective, people, especially potential encroachers, must be convinced that there is good reason to obey the restrictions. Therefore, education and raising awareness are the important parts of a protected area programme.
No-fishing areas are still astoundingly rare in the marine environment, are set aside to protect important spawning grounds or to provide a refuge area for species that are heavily fished in surrounding waters. Here, they have an opportunity to replenish their numbers and grow to a larger size, which benefits the fishery outside as well as the fish.
Despite the popularity of protected area approach in the national and international conservation community, these areas are not always defined and protected in a way that maximises benefits to the ecosystem. For instance, protected areas are often defined first by shoreline features or boundaries, then by bottom topography, and rarely by water circulation patterns. Yet, water circulation is probably the most important to pelagic communities and is critical to benthic communities as well.
Ten generally supported guidelines can be listed to guide the establishment or re-planning of protected areas that will have biodiversity conservation as their central or major purpose: