Coral and Reefs
Coral reefs are large underwater structures made up of the skeletons of reef-building corals, tiny polyps that create hard exteriors. These corals build up in colonies, usually on older coral, but also on rocks and other hard surfaces.
These reefs take up less than one percent of the land area underwater (about half the size of France), but help support over twenty-five percent of known marine life. The reefs are also known as the 'rain-forests of the sea' because of the diverse amounts and kinds of life present.
Coral Bleaching and Ocean Acidification
Coral is highly sensitive to temperature change. When the water warms significantly, corals expel the algae that lives in them. This phenomenon is called coral bleaching, as the algae is what gives coral it's color. I found an article on Upworthy that shows amazing shots of coral before and after a 2 degree change in water temperature. The time-lapse gifs are especially powerful.
Ocean acidification is a process that happens when seawater absorbs CO2. Normally the ocean absorbs about 30% of released CO2. The more that gets released into the atmosphere, the more gets absorbed by the ocean. The additional acidity in the water inhibits coral's ability to produce their protective shells.
3D Printed Reefs
Coral farming is the process of cultivating coral in nurseries. To better study the challenges faced by coral, some groups have begun using 3D printed coral reefs as underwater nurseries. Baby corals can attach themselves to the artificial reefs and grow from there. Corals can also be cultivated by attaching a splinter of coral from another reef to the 3D printed one. Scientists can then study the coral that grow there. The reason for using an artificial reef is that it takes a very long time to grow even a small reef.
While the created reefs don't solve the immediate challenges that the corals face, people are researching alternative ways to utilize the underwater models. Proposals include using them as something like starter-homes for reefs in more suitable areas, letting reef inhabitants use them as temporary shelters, or regenerating existing reefs.