Most of us have seen footage of flickering, glowing deep sea creatures. But a new study shows that fully 75% of the ocean's creatures bioluminesce, which means that the depths of the ocean may not be nearly as dark as we might have thought. And in some categories, like jellyfish and jellyfish-like creatures (siphonophores), up to 99% of the species is able to glow.
Many of these creatures give off only a faint glow. So faint, in fact, that until recently, cameras were not able to capture it. However, the glow is bright enough for the creatures' purposes - and for those of their predators, as well.
Earlier studies were no doubt also thrown off by the fact that many of these creatures can and do turn their bioluminescence on and off at will. Light attracts food, but it also attracts predators.
And it's expensive to produce, to boot. A deep sea creature needs to preserve its energy, given how difficult it must be to make a living in the depths.