--- title: "Deep-Sea Bioluminescence: Why Most Deep Animals Glow" url: https://thesea.org/deep-sea-bioluminescence/ date: 2026-11-13 modified: 2026-11-13 lang: en author: "Blane Perun" description: "TheSea.Org▸Bioluminescence▸Deep-Sea Bioluminescence Bioluminescence in the Deep Sea — Why Three-Quarters of Deep Animals Glow Bioluminescence & Plankton By Blane Perun November 13, 2026 10 min read Why is bioluminescence so..." categories: - "Coral Reef" word_count: 1943 --- # Deep-Sea Bioluminescence: Why Most Deep Animals Glow [TheSea.Org](/)▸[Bioluminescence](/bioluminescence/)▸Deep-Sea Bioluminescence # Bioluminescence in the Deep Sea — Why Three-Quarters of Deep Animals Glow Bioluminescence & Plankton By [Blane Perun](/about-blane-perun/) November 13, 2026 10 min read Why is bioluminescence so common in the deep sea? Below about 1,000 metres no sunlight reaches, and from 200 metres down it is only a dim blue glow, so light made by animals becomes one of the most useful tools there is. A survey off California found that **about 76% of animals observed in the open water column** could make light. Deep-sea animals use it to **hide their silhouettes, lure prey, find mates and startle or expose predators**. Quick facts Share that glowAbout three-quarters of water-column animals Twilight zoneAbout 200–1,000 m Midnight zoneBelow about 1,000 m Usual colourBlue to blue-green Rare colourRed (some dragonfish) Common light moleculeCoelenterazine Main usesCamouflage, hunting, signalling, defence Independent originsDozens across the tree of life On land, glowing animals are a novelty: fireflies, a few fungi, some worms. In the deep ocean the rule is reversed. Most of the animals drifting and swimming in the dark water below the sunlit surface layer can make their own light, and many of them have several different ways of doing it. Bioluminescence there is not a curiosity; it is the main language of the largest habitat on Earth. This page explains why light is so common in the deep sea, how animals use it, and what the most famous glowing deep-sea animals actually do with their light. For the basics of how marine light is made, start with our [bioluminescence](/bioluminescence/) guide. How much of the deep sea glows? The best modern estimate comes from Séverine Martini and Steven Haddock at the Monterey Bay Aquarium Research Institute (MBARI), who went through years of remotely operated vehicle (ROV) video from the surface to nearly 4,000 metres. They classified every animal seen in the water column by whether its group is known to be bioluminescent. Their 2017 study concluded that about three-quarters of the animals observed, roughly 76%, were capable of producing light. The proportion was fairly consistent from the surface down to great depth, though the types of animals doing the glowing changed. Jellyfish, siphonophores, comb jellies, worms, crustaceans, squid and fish all contributed. That figure applies to animals in the open water. On the deep seafloor, bioluminescence is less common, though still widespread among some groups, such as sea pens, brittle stars and some corals. The open water of the deep sea is the most luminous environment on the planet simply because there is nothing else to see by. ![Dragonfish with a glowing chin barbel in the midnight zone, an example of deep-sea bioluminescence](https://thesea.org/wp-content/uploads/deep-sea-bioluminescence-1-thesea-org-by-blane-perun.webp)Dragonfish with a glowing chin barbel in the midnight zone, an example of deep-sea bioluminescence Twilight zone and midnight zone Sunlight fades quickly in seawater. Red light is absorbed in the first few metres and by about 200 metres only a faint blue glow remains. This dim layer, from roughly 200 to 1,000 metres, is called the twilight or mesopelagic zone. Below 1,000 metres, in the midnight or bathypelagic zone, no sunlight that animals can use reaches at all. The two zones favour different uses of light. In the twilight zone, animals still have to worry about being seen as dark silhouettes against the faint light from above, so camouflage by counter-illumination is common. In the midnight zone there is no background light, so bioluminescence is mostly used for hunting, signalling and defence. Many animals move between the zones every day: the daily vertical migration of lanternfish, krill and other plankton from the depths to the surface at night is the largest animal migration on Earth by mass. | Use of light | How it works | Example | | ------------ | ------------ | ------- | | Counter-illumination | Belly lights match faint light from above to erase the silhouette | Hatchetfish, lanternfish, many squid | | Lure | A glowing bait draws prey within reach | Anglerfish, some dragonfish | | Searchlight | Light used to see prey | Dragonfish (red light), flashlight fish | | Mate signals | Species-specific photophore patterns or flashes | Lanternfish, ostracods | | Startle and escape | Sudden flashes or glowing clouds confuse predators | Vampire squid, deep-sea shrimp | | Burglar alarm | Light attracts a bigger predator to the attacker | Atolla jellyfish | Hiding with light: counter-illumination It sounds backwards to hide by glowing, but it works. In the twilight zone, a predator looking upward sees the faint light from the surface, and any animal above it shows up as a dark shape. Many fish, squid and shrimp solve this with rows of light organs, called photophores, along their bellies. They adjust the intensity and colour of the light to match what is coming from above, so their silhouette disappears. Hatchetfish, with their thin silver bodies and downward-pointing photophores, are a classic example. Lanternfish, the most abundant vertebrates in the deep sea, also carry belly photophores, and the arrangement of their lights differs between species, which probably helps them recognise one another. Some [lantern sharks](/lantern-shark/) use counter-illumination too. Hunting with light: lures and red searchlights In the midnight zone, a glowing spot is one of the few things that can attract attention, and predators exploit that. The female deep-sea anglerfish carries a modified fin spine tipped with a glowing lure, the esca, which in many species is lit by symbiotic bacteria; small animals that approach the light are snapped up. See our [deep-sea anglerfish](/deep-sea-anglerfish/) and [triplewart seadevil](/triplewart-seadevil/) pages. Many dragonfish have a glowing barbel hanging from the chin that probably serves the same purpose. A few dragonfish go further. Most deep-sea animals cannot see red light, because there is no red light at depth and their eyes have lost sensitivity to it. Dragonfish such as the stoplight loosejaw (*Malacosteus*) produce red light from organs below their eyes and can see it, thanks in part to a pigment derived from chlorophyll that they apparently obtain through their diet. In effect, they hunt with a private searchlight that their prey cannot see. ~76%Water-column animals able to glow (MBARI survey) 1,000 mRoughly where usable sunlight ends BlueMost common deep-sea light colour ![Deep-sea shrimp spewing a glowing blue cloud, a defense using deep-sea bioluminescence](https://thesea.org/wp-content/uploads/deep-sea-bioluminescence-2-thesea-org-by-blane-perun.webp)Deep-sea shrimp spewing a glowing blue cloud, a defense using deep-sea bioluminescence Defending with light: flashes, clouds and burglar alarms Defence may be the most common use of all. Many animals flash brightly when touched, which can startle an attacker for long enough to escape. Some shrimp and squid squirt glowing fluid instead of dark ink, leaving a predator lunging at a bright cloud while the prey slips away in the darkness. The vampire squid releases a sticky cloud of glowing particles from its arm tips. Some worms and jellies shed glowing body parts that keep shining as decoys. The most elegant idea is the burglar alarm. When the deep-sea jellyfish *Atolla* is grabbed, it produces a spinning, pinwheel display of blue light that can be seen from a distance. The theory is that the display attracts larger predators that may attack whatever is attacking the jellyfish. Edith Widder used an electronic lure that imitated this display, called the e-jelly, along with a camera system designed to avoid bright lights, and in 2012 that approach helped capture some of the first video of a giant squid in its natural habitat. Glowing deep-sea jellyfish Gelatinous animals are among the brightest light makers in the deep. Many deep-sea jellyfish, such as *Atolla* and the helmet jellyfish *Periphylla*, glow when disturbed, and comb jellies can produce flashes of light along their bodies. Siphonophores, including the giant *Praya dubia*, carry luminous cells along their great length. These animals are fragile and were long underestimated because they fall apart in trawl nets; ROVs and submersibles revealed how common and luminous they really are. Our [bioluminescent jellyfish](/bioluminescent-jellyfish/) and [giant siphonophore](/giant-siphonophore/) pages cover them in more detail. How the light is made Almost all bioluminescence comes from a reaction in which an enzyme (luciferase) or a photoprotein oxidises a light-emitting molecule (luciferin). Remarkably, many unrelated deep-sea animals use the same luciferin, coelenterazine, including jellyfish, comb jellies, many crustaceans, squid and fish. Some make it themselves; many probably get it from their food. Others use bacterial symbionts, and a few, such as some krill and dinoflagellates, use quite different chemistry. Bioluminescence has evolved independently dozens of times, with a 2021 review by Emily Lau and Todd Oakley counting at least 94 separate origins across the tree of life, the large majority of them in the sea. Light organs have been built from modified skin glands, from muscle, from eye tissue and from pockets that house bacteria. Many animals add reflectors made of stacked crystals behind their photophores, pigment screens around them and colour filters in front, so the light can be aimed, shaped and tuned to match the background. Some can even change the intensity of their belly lights within seconds as they swim up and down, keeping their camouflage matched to the changing light above them. For a closer look at the bacteria that light some of these organs, see [bioluminescent bacteria](/bioluminescent-bacteria/). That repeated evolution is a strong sign of how useful light is in the dark ocean. Most deep-sea light is blue, because blue travels furthest in seawater and most deep-sea eyes are tuned to it. My take: the biggest light show we rarely see I have done many night dives over the years, from the Caribbean to the Pacific, and even in shallow water, a night dive shows how much of the sea runs on its own light: waving a hand through the water can trigger sparks from plankton. But that is the faint edge of a much bigger display. The deep sea is the largest living space on Earth, and most of its residents are signalling, hiding and hunting with light we almost never get to see in person. Nearly everything we know comes from submersibles, ROVs and cameras designed to watch without scaring the animals away. If you want to get closer to deep-sea light without a submersible, the best options I would recommend are public aquariums with dedicated deep-sea and jellyfish exhibits, and the excellent ROV video archives that research institutes such as MBARI make freely available. Our [deep-sea creatures](/deep-sea-creatures/) guide is a good next step. ![Anglerfish with a glowing lure in the dark, the best-known deep-sea bioluminescence](https://thesea.org/wp-content/uploads/deep-sea-bioluminescence-3-thesea-org-by-blane-perun.webp)Anglerfish with a glowing lure in the dark, the best-known deep-sea bioluminescence Frequently asked questions What percentage of deep-sea animals are bioluminescent? About 76% of animals observed in the water column off California, according to a 2017 MBARI study. Why do deep-sea animals glow? To camouflage themselves, attract prey, find mates and startle or escape predators in the dark. Why is deep-sea bioluminescence mostly blue? Blue light travels furthest in seawater, and most deep-sea eyes are most sensitive to it. Which deep-sea animal makes red light? Some dragonfish, such as the stoplight loosejaw, which can also see red light. Do deep-sea jellyfish glow? Many do, including *Atolla*, whose pinwheel display may act as a burglar alarm. Is the deep sea completely dark? Below about 1,000 m there is no sunlight, but animal light flashes and glows throughout. Sources & further reading - Martini, S. & Haddock, S.H.D. (2017). Quantification of bioluminescence from the surface to the deep sea demonstrates its predominance as an ecological trait. *Scientific Reports* 7: 45750. - Haddock, S.H.D., Moline, M.A. & Case, J.F. (2010). Bioluminescence in the sea. *Annual Review of Marine Science* 2: 443–493. - Lau, E.S. & Oakley, T.H. (2021). Up to 100 independent origins of bioluminescence across the tree of life. *Biological Reviews*. - Widder, E.A. (2010). Bioluminescence in the ocean: origins of biological, chemical, and ecological diversity. *Science* 328: 704–708. - MBARI: Bioluminescence research and video archive. Continue reading More about ocean light [Deep SeaDeep-Sea CreaturesLife in the dark ocean. ](/deep-sea-creatures/) [Deep SeaDeep-Sea AnglerfishThe glowing lure. ](/deep-sea-anglerfish/) [BioluminescenceBioluminescent BacteriaLight organs and milky seas. ](/bioluminescent-bacteria/) BP Last updated November 13, 2026 Written by Blane Perun Blane Perun has been exploring Earth’s oceans and marine life for over 25 years. Founder of TheSea.Org in 1999, underwater photographer, coral aquaculture pioneer, and explorer of 80+ countries. [About Blane Perun →](/about-blane-perun/) [More on bioluminescence →](/bioluminescence/)