In the sea, the mesophotic zone is the twilight zone in the water column where only the blue wavelength of light penetrates. Located at a depth of 40 to 180 m according to the regions of the world, it harbours deep-water reef-building corals, from the poles to the equator. The study of those largely unknown species is being stepped up. Indeed, some of them could be re-implanted on the surface in damaged reef areas. Monaco Explorations have already devoted several missions to them.