Do you now or have you ever eaten fish ?
Protecting the resource that provides us with vast amounts of food and entertainment is important.
Here's a census of marine life - very interesting resource.
Consider the cost if "someone else" fails to do a good job on this one. Consider the immense value of these services to humankind and take a look at the map. "Precious little" would be an understatement; learn more about this issue and do something today.
The best I can come up with as a guerilla idea is creating stencils like those used in towns including San Francisco. A freshwater example from Wikipedia is shown here at left. A group might then use chalk instead of spraypaint with the stencils to prompt municipal interest, draw media attention, and increase awareness, hopefully facilitating a dialog that results in municipalities deciding to replace the chalk with spraypaint. Maybe even adding local awareness campaigns about dumping chemicals down drains, increasing awareness about recycling services already offered for hazardous substances ranging from oils to antifreeze. Our freshwater resource here in Chicago seems just as important as the marine ecosystems discussed in the links to the MPAs. Although our systems filter out much of what we put in, increasing awareness about WHY not to pollute our water system and the costs of action vs. inaction seems like an idea frought with possibility...