A glowing jellyfish

A glowing jellyfish © olgalngs/Shutterstock.com

Bioluminescence: light in the dark

Lanternfish are one of many animals that light up the ocean with their glowing bodies.

Watch fish expert Ollie Crimmen explain more about these deep-sea dwellers.

Lanternfishes have light-producing organs on their bodies that are called photophores.

This light is created by a chemical reaction, and it is one example of a phenomenon called bioluminescence. 

 

What is bioluminescence?

Bioluminescent organisms produce and radiate light. There are thousands of bioluminescent animals, including species of fishes, squid, shrimps and jellyfish.

The light these creatures emit is created inside their bodies, meaning they are able to glow and glitter in complete darkness.

Some of the planet's bioluminescent animals live in the deep ocean (although not all of them). Many exist in the twilight zone, the part of the ocean from 500 to 1,000 metres deep, which is always dark in its lower margin.

In this environment, the light some animals can create for themselves is fundamental to survival. It is thought that up to 90% of life in the twilight zone creates light in some form.

A comb jellyfish

Most organisms that live in the twilight zone can produce light © Orin Zebest, licensed under CC-BY-2.0

 

How does bioluminescence work?

Bioluminescence has evolved independently many times during the history of life on Earth, which means many different species developed the ability to produce light separately.

The light that living creatures can produce is created by a chemical reaction. For this reaction to happen a plant or animal must carry a molecule called luciferin, plus one of two enzymes called luciferase and photoprotein.

When luciferin chemically reacts with oxygen, it releases energy in the form of light. Different animals and plants contain different types of luciferin.

The most common light produced in the ocean is green and blue, as these wavelengths travel further through water. Some fish can also create red light, though is much rarer, and on land fireflies glow yellow.

Bioluminescence in the waves

Tiny creatures and bacteria can make the ocean glitter with light © Kris Williams, licensed under CC BY-NC-ND 2.0

 

Tiny living lightbulbs

As well as animals, many miniscule plant-like species and fungi can also create bioluminescence. About 75 species of fungi are capable of giving off an eerie, green light, possibly to attract insects which will help to spread their spores. Most of these species live in tropical rainforests.

Dinoflagellates make light shows on the surface of the ocean. These tiny, single-celled organisms get their energy from sunlight, like plants do. When disturbed, these gatherings of microbes create beautiful light patterns in oceans all over the world.

Bacteria can shine both on land and underwater. They can live independently in seawater or sand, or inside a bigger organism. For instance, bobtail squid host bioluminescent bacteria (Vibrio fischeri) in their underbellies.

The bacteria get food from the squid's body and in return emit blue light, which can appear to travel in waves along the squid's body, helping with camouflage.

What is bioluminescence for?

Animals can often control when they produce light, and they make use of it in many different ways. Even in one organism bioluminescence can have multiple uses.

In the deep sea, light is used to attract prey or a mate, to frighten away predators, to observe surroundings, or - like the bobtail squid and the lanternfish - for camouflage and protection.

Some fungi emit light permanently, even in daylight. But many animals use bioluminescence in short bursts. Fireflies flash brightly to attract mates, whereas jellyfish do the same thing to startle predators.

Some beetles use light to make themselves look a little larger, and anglerfish use a light organ to entice their prey.

Dive in

Our oceans are changing. Find out why we're protecting life underwater.