If you have ever watched the ocean at night in Cape Town, you might have noticed the waves glowing blue. This blue light is being produced by lots of tiny algae called dinoflagellates in a process called bioluminescence (the ability of living things to produce light).
How does it work?
Bioluminescence is the result of a chemical reaction. When a protein called luciferin reacts with oxygen, light is released. Another protein called luciferase helps the chemical reaction work. In many animals, this chemical reaction happens inside a structure called a photophore.
Scientists think that bioluminescence evolved from photosynthesis. Photosynthesis is the process that plants use to make food from sunlight, carbon dioxide and water.
Bioluminescence is used by both predators (animals which eat other animals) and prey (animals which are eaten by predators).
How is bioluminescence used to escape from predators?
Some squid species release a sticky bioluminescent substance into the water when they are threatened by a predator. This has two effects. Firstly, the glowing substance startles the predator, giving the squid time to escape. Secondly, the bioluminescent substance sticks to the predator. This attracts nearby fish which come and eat the predator.
How is bioluminescence used for camouflage?
Many aquatic animals have lots of photophores on their underside. This means these animals can release light from underneath their body. Animals can make their photophores release light which is the same colour as the light coming from the surface of the ocean. This makes the animal blend in with its surroundings when looked at from below. This method of camouflage is called counterillumination.
How is bioluminescence used to catch prey?
The anglerfish is a fish which lives deep in the ocean where there is no sunlight. This makes it hard to find prey to eat. To solve this problem, the anglerfish uses bioluminescence to attract nearby fish to eat. To do this, the anglerfish dangles a glowing sac of bioluminescent bacteria above its mouth. This bioluminescent lure attracts nearby animals into the mouth of the anglerfish.
The cookiecutter shark has found a way to use counterillumination and a lure together. Like many other marine animals, the cookiecutter shark has lots of photophores on its underside to camouflage it from below. However, there is a small patch on the shark’s underside which has no photophores. This means that most of the cookiecutter shark’s body is camouflaged from below, except for this small dark patch where there are no photophores. Nearby animals which see this small dark patch might think that it is a small fish for them to eat, when in fact it is a shark! This attracts these animals to the cookiecutter shark, which surprises them and eats them.
Is bioluminescence only seen in the oceans?
Some animals on land, such as fireflies, bioluminesce. However, bioluminescence is much more common in the oceans than on land. Bioluminescence is one of nature’s most beautiful inventions and is used by animals in lots of clever ways.