Bioluminescence
in the deep ocean

Bioluminescence is light produced by living organisms. It is extremely common in the oceans and occurs in all oceans at all depths. Many deep-sea creatures are bioluminescent.

The light is produced by symbiotic bacteria within light-emitting cells called photophores. It is produced by a chemical reaction when a substance called a luciferin is oxidized. When the light is released, the luciferin becomes inactive until it is replaced by the animal. Some animals can make luciferin themselves, or it may be synthesised by symbiotic bacteria inside the photophore.

The photophores, or light-emitting cells, range from simple clusters of cells to complex organs surrounded by reflectors, lenses, colour filters and muscles. The most common coloured light produced by marine organisms is blue. This is also the colour that penetrates furthest through water.

Deep-sea fish with bioluminescence

In the dark of the ocean, bioluminescence can help organisms to survive. Several deep-sea fish, such as anglerfish and viperfish, use bioluminescence as a lure to attract prey. The dangling appendage that extends from the head of the anglerfish has a light organ at the end which attracts small animals to within striking distance.

Other fish, such as lanternfish (myctophids), have light organs on their sides and bellies. Lights on the underside of a fish such as a lanternfish or bristlemouth break up the silhouette of the fish's body. This makes the fish harder to see from below, and helps protect it from predators. Light organs also help fish to recognise mates. Each species of
lanternfish has a distinct pattern of lights.

Squid with bioluminescence

Bioluminescence is common among squid. It is estimated that two-thirds of all squid genera include bioluminescent species. Light organs, or photophores, can be found nearly anywhere on the body of a squid. The most common places are the eye (ocular photophores), mantle, head and arms, internal organs (visceral photophores), funnel, and
tentacles.

Images
Image 01
Lightfish, also called bristlemouths, are common small bioluminescent fish in the mesopelagic. They have light organs on their bellies which help hide their outlines.

Lightfish
Cyclothone species.

Courtesy of DeepSeaPhotography.Com
Image 02
Lightfish/bristlemouth, Ross Sea
Gonostoma species

Photograph by Peter Marriott
Courtesy of NIWA
Image 03
Lanternfish, Ross Sea
Gymnoscopelus brauer

Photograph by Peter Marriott
Courtesy of NIWA
Image 04
The dragonfish has a fishing rod, or lure, with a light at the end hanging from its chin.

Dragonfish, Ross Sea
species unknown

Photography by Peter MacMillan
Courtesy of NIWA
Image 05
Lanternfish
Lampanyctodes hectoris

Digital reconstruction
Courtesy of DeepSeaPhotography.Com
Image 06
The black anglerfish, or sea devil, has a glowing lure and can catch prey larger than itself.

Black anglerfish
Melanocetus johnsonii

Digital reconstruction
Courtesy of DeepSeaPhotography.Com
Image 07
Antarctic anglerfish

Anglerfish

Photograph by Andrew Stewart/Michelle Freeborne
Image 08
The vampire squid lives in very deep waters around the world. This small squid has glowing tips on its tentacles.

Vampire squid
Vampyroteuthis infernalis

Courtesy of Steve Haddock, DeepSeaPhotography.Com
Image 09
The eyelid of the colossal squid is pulled back to show part of the light organ (photophore) at the rear of the eyeball. The eye is turned forward.
Image 10
The light organ can be seen at the rear of the left eyeball of the colossal squid. The specimen has been lifted out of the preservative and placed in the display tank.
Image 11
A top-down view of a googly-eyed glass squid, a close relative of the colossal squid. The stalked eyes have light organs, just like the colossal squid.

Courtesy of DeepSeaPhotography.Com

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