I had the pleasure a little while ago of seeing some photos of coral reefs up close and personal at the Radcliffe Institute at Harvard. It was a pleasure to see the photos, but what is in the photos is not very uplifting. They are pictures taken by photojournalist David Arnold in the same spot as several underwater photographers took as early as 1970. It is called Double Exposure and really highlights how things have changed in the last decades. The website is really worth looking at: http://www.doublexposure.net/about-us/.  Here is an example:

The left is 1980 and the right is 2011 in South Carysfort Reef in South Florida. It is really worth going to the website to see all the images and move the center line so you can see the entirety of both pictures and how it has changed.