MPAs are one of many management or conservation tools that must be used in conjunction with other strategies. The answer to the question "Do MPAs work?" depends on the goal of the MPA. The goal of MPAs can range from the protection of ecosystem biodiversity to enhancement of a specific fishery or the protection of a particular species (e.g., red sea urchins or northern bottlenosed whales). The merit of a specific MPA or network of MPAs must be judged on the success to which it achieves its set goal. In general, many fisheries reserves are designed to have regional effects, whereas many biodiversity reserves focus on protecting species within a defined area. Potential goals that have been suggested for MPAs include:

	Enhancement of local fisheries. Reduction of localized fishing pressure tends to have a dramatic effect on the numbers and size of exploited fish. Larval fish originating from elsewhere in the marine ecosystem are thought to supply MPAs with fish.
	Enhancement of regional fisheries. The operative theory is that larvae produced by mature fishes breeding within MPAs will disperse outside the MPA and enhance local stocks. Few scientific studies have examined the impact of an MPA on surrounding "fished" areas.
	Local enhancement or protection of species richness. The protection afforded by MPAs often affect numerous complicated ecological processes and the results on species richness can be variable. In some cases, protection from physical disturbance like trawling or protection from harvest can increase species richness. In other cases, the composition of the community will be altered, but actual species richness will not change.
	Regional enhancement of biodiversity. The objectives of the MPAs are to be able to export local effects (larvae, invertebrates, fish, etc.) into unprotected areas. More research is necessary to better understand if this objective is realistic.

   While there is general consensus that MPAs enhance biodiversity within their boundaries, there is on-going debate as to their merits for enhancing biodiversity and sustaining fisheries outside of their boundaries. Scientific investigations of MPAs as fisheries management tools vary in their findings. Examples of scientific literature concerning this debate can be found at the federal MPA library reference list at http://mpa.gov/mpaservices/library/referencelist.html