Marine Protected Areas are established with one of three objectives in mind.
To conserve natural heritage: The goals are to protect and restore the biodiversity within the ecosystems of an area. Some of examples include most national marine sanctuaries and national wildlife refuges.
To conserve cultural heritage: This would include providing protection to historical artifacts, such as a shipwreck. This may include some of the national marine sanctuaries, national and state parks and historic monuments.
Sustainable Production: The area would be managed in a way that supports the extraction of living resources (like fish, shellfish, plants, etc) that depend on the protected areas habitat for feeding, mating, spawning, etc. Examples might include some wildlife refuges, and certain fishing areas. (http://marineprotectedareas.noaa.gov)
Allows ecosystems to recover and reestablish after natural or human impacts
Fostering healthy marine ecosystems can lead to increased seafood production, good water quality, and coastal protection from events like hurricanes
Supports fisheries inside and outside of the MPA as species move in and out of the area
Protects significant habitats
Creates opportunities for education and research
Provides potential for recreation and tourism to grow
Protects areas that have cultural significance so that they can be enjoyed by future generations