Coral Reefs as Resources

The US Geological Survey expends a lot of time and manpower on resource estimation: energy, minerals, biological (in several ways). The following question came at me sideways, and caused me to really think.

Q: 
What are some resources that coral reefs provide?
What are some topographical features around coral reefs?
- Maya R

A.
The main resources that coral reefs provide - that most people talk about at least - is biodiversity. This is a hard thing to quantify or explain, but if reefs all die from acidification and heat related to climate change, then much of the food-chain in the oceans would be severely disrupted. Some new drugs have already been derived from unique reef species, so that is another potential future resource. I believe that there are some entities that have mined reefs for the calcium carbonate that they contain, but this is like the Spaniards four centuries ago melting down precious Aztec and Incan gold artifacts. Trying to capture a "resource" this way destroys 95% of its value.

Coral can only grow where there is light, so this generally means the fringe waters of islands and coastlines, and only in tropical latitudes. In the Pacific, this often means that there are reef rings around volcanic islands or below-the-surface guyots. As the original core rocks of the volcanic island weather and crumble down, this generally means that the remaining topographic feature is an atoll: a coral ring with a shallow lagoon inside. There is very little topographic relief above the water line. The topographic fall-off of an island reef system tends to be steep, however. I've Scuba-dived some of these and the reef "wall" looks like it just goes straight down into the black depths. There are also reef systems on continental margins, and the Great Barrier Reefs of Australia and Belize are examples. Bathymetry tends to follow this characterization as one moves outward: the continental margin, then shallow water, then a reef system, than a steep fall-off to the continental shelves or in some cases the oceanic abyssal plain.

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