No, coral reefs aren’t really made from sugar, spice, and everything nice. In fact, they’re made from the calcium carbonate that is secreted by corals, which are marine invertebrates. Coral reefs are actually just made up of tons of tiny animals and live off of very few nutrients. Most coral reefs are composed of stony corals, which consist of polyp clusters, which are in the same group of animals as sea anemones and even jellyfish. So basically, coral reefs are comprised of exoskeletons!