Close-up of coral fluorescence in a reef lab
This video shows various scleractinian corals under narrow-bandwidth blue light, which excites the fluorescent proteins in the epidermis of the animals. Fluorescence is a phenomenon where an object absorbs light of a particular wavelength (colour), and emits it at another wavelength (colour). It is still not clear why corals produce fluorescent proteins, but it seems to protect them from harmful UV-radiation and excess (sun)light.
Using time-lapse, the contractile and expansion behaviour of coral polyps is also visualized in this video.