Here is a brief (not-exhaustive) list of possible goals that could be included in any plan for Marine Protected Areas (MPAs):
Conservation of Biodiversity:
An MPA can be set up preserve an ecosystem as a whole. Some would argue that there is intrinsic value in the protection of representative habitats. Additionally, there is the economic/practical value of the marine ecosystem services that could be preserved by MPAs. The positive impacts can be maximized by preserving a diverse array of ecosystems and species.
Protection of Individual Populations:
An MPA can be used as a refuge for depleted, rare, threatened or endangered species. These could be most effective if targeted at critical habitats or critical stages of the life cycle, such as breeding, feeding, etc.
Habitat or Population Recovery:
MPAs can be used to give time for a damaged or depleted entity to recover. By halting the damaging activity, such as trawling, dumping, etc. time is hopefully given for the impacts of the activity to wear off.
Fishery Management:
Fishery reserves can play a significant role in maintaining the long-term sustainability and profitability of a fishery. Primarily, the benefit derives from control of exploitation rates. Fishery reserves can also be deployed to protect the most vulnerable life stages of a target species, improving reproductive success and overall biomass.
Provide Scientific Knowledge:
Often, one of the difficulties of studying the impacts of anthropogenic activities is the lack of true baseline data. This problem occurs in many, diverse fields such as fish population dynamics to pollution studies. Given time, MPAs could show scientists what an "undisturbed" environment looks like, allowing for more effective study of outside areas.
Provide Educational Opportunities:
The oceans are an integral part of our planet that all educated citizens should have some understanding of. MPAs provide an opportunity for the general public to learn about the oceans themselves and human impacts thereon. This area is essential, as it provides the political will and impetus for any future efforts at protecting the oceans.
Improved Recreation and Tourism:
Areas near MPAs can benefit economically from the people that it will draw. Aesthetic improvements, auxiliary services, related attractions can all work together as the basis for non-consumptive uses of the MPA.
Environmental Benefits and Ecosystem Services:
Energy, erosion protection, filtering, nutrient cycling, remediation are all beneficial functions of marine ecosystems that can be supported by MPAs.
Cultural Heritage:
Areas of particular cultural value can also be protected by MPAs. Examples include prominent shipwrecks, archaeological sites, the locations of traditional practices, and areas of particular aesthetic beauty.