Marine protected areas differ if how much protection they offer, and some may in reality not offer much more protection than you get in the rest of the ocean anyway. Why does this happen? Politics.
One of the main problems with valuing ecosystem services lies in how they are valued, because there is no one set procedure for doing so. What you can end up with is a value that only reflects what you chose to place a value on.
So my lovely readers living out in the USA, just how much of the marine ecosystem in your state waters is afforded strong protection? Probably not that much.