Talk:Giant Coral Tubes/@comment-70.129.119.119-20150812211132/@comment-444327-20160927125616

I can see where you're coming from since it's a source of Calcium Carbonate, but generally coral is a colony of living organisms that build structures like these out of Calcium Carbonate, which they naturally secrete, to protect themselves. Some can rely on sunlight to provide them with energy (very similarly to photosynthesis but not quite) which is why you often see coral clustered around shallow tropical seas, including on this game.

Even the Databank entry of this particular fictional species states they're shaped this way to maximise water and nutrient flow, so it's an evolutionary thing.