This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Between 200 and 1,000 meters down, in what oceanographers call the twilight zone, light from the surface is fading out and darkness is closing in. NOAA states that 80 percent of the animals living at that depth are bioluminescent, meaning they generate their own light through a chemical reaction inside their bodies. That is not a rare adaptation restricted to a few strange fish. It is closer to the default condition of life at this depth, uncommon on land and yet ordinary here. NOAA notes the exact purpose is not always clear, but documents bioluminescence being put to work for finding food, for reproduction and for defense, a single trait doing several different jobs depending on the species carrying it. The scale of the number is worth pausing on: at a depth where a human eye finds almost nothing but blackness, the overwhelming majority of the animals sharing that water are quietly generating their own light, all the time, for reasons science is still working out. It reframes what an unlit ocean actually looks like from the inside. To a human observer sinking through it with no equipment, the twilight zone reads as darkness. To the animals living there, by NOAA's own figure, it is anything but dark.