From Rueters: A new UN study suggests that a network of small marine protected areas may be more effective than few big MPAs.
First, what is the basic economic problem here? That is, why do we need MPAs in the first place?
What type of solution (command-and-control or incentives) would we classify marine protected areas as?
What problems arise with MPAs?
What are the goals of an MPA? Are most MPAs reaching those goals?
Read about MPA effectiveness here and here.
Here is an excellent article from Resources for the Future on the economic and social implications of MPAs.
Here is an informative site from NOAA regarding economics and MPAs.