A close up profile of an adult anglerfish female from the Linophryne family collected in the northern region of the Gulf of Mexico. © 2016 DEEPEND/ Dante Fenolio
Descend two hundred meters (about 656 feet) below the surface and the ocean is reduced to total darkness. Creatures that live beyond the Twilight Zone spend their lives almost entirely in a near-limitless black expanse, save for a group of luminous fishes, invertebrates and bacteria that have evolved a special adaptation: bioluminescence.
Bioluminescence is the predominant source of light in the largest fraction of the habitable volume of the earth—the deep ocean. It’s thought that 90 percent of open ocean organisms produce light of some kind, and that this ability that has evolved many times. It serves a few predictable purposes, like possibly signaling to members of the same species or illuminating prey, along with some capricious ones like the ability to eject luminescent body parts in order to distract a predator.