English edit by Katy Shoemaker
As previously described in the blog, we know more about space than we do our own oceans. As we begin exploring the bottom of the ocean, we realize just how much is still a mystery. Sunlight cannot reach the bottom of the ocean, so there is no photosynthesis, which is the primary energy source for most food chains. Despite this, there is plenty of life in the deep ocean, and, believe it or not, there is also lots of light! That’s right, a study published in Scientific Reports estimated that over 75% of the marine organisms living from the surface all the way down to 4000m can create light, a phenomenon called bioluminescence.
A broad variety of animals like fish, worms, jellyfish, crustaceans, squid, and octopuses can emit their own light. This can create a true underwater light show! Bioluminescence is so widespread and important, it is considered an ecological trait for marine animals. You must be wondering, why is it so important to produce light? Well, thanks to science, we can help cure a bit of that curiosity on this underexplored subject. Current research shows that organisms create their own light for a number of different reasons, including:
Defend themselves from predators
Through camouflage: the animal can obtain similar colors as those of its environment in order to hide and escape predators;
Image: A squid using bioluminescence to hide in the bottom of the ocean. It produces light that perfectly matches the color and intensity of down welling sunlight in the ocean to it hides its silhouette. This is called counterillumination. Source
By distracting the predator: some animals can expel luminescent material, creating a look-alike creature to deceive their predator while escaping
Image: This shrimp is capable of producing bioluminescence in two ways: by expelling a blue secretion from its mouth to deceive predators, as well as lighting up specific body parts like articulations, abdomen and eyes. Source
Image: Tomopteris helgolandica is a sea worm that is capable of producing yellow light, rare for luminescence. In this case, bioluminescence is emitted in the tip of the parapodes (structures that look like tiny legs) when the animal is disturbed. It is believed to distract predators. Source
To find a partner in the dark must not be easy. Some species emit light flashes to attract potential sexual partners or even, like this female glow worm, emit constant light that is only turned off once they mate.
To get food
Some fish can be attracted by small light dots emitted by predators, who capture prey as they approach. This is the tactic of the Angler Fish, pictured here.
Image: Angler fish. Source
Organisms can bioluminesce in two different ways: by associating with bioluminescent microbes or by creating the effect themselves. Light is emitted by mixing luciferin, a light producing compound, with luciferase, an enzyme that catalyzes the reaction.
Images: Juvenile octopus (above) and juvenile squid (below) in Tahiti waters.
Bioluminescence can be useful to humans as well. Scientists can use chemical compounds derived from glowing animals in medical research to illuminate cells for viewing through a microscope. These compounds can be used to differentiate cancerous cells from healthy ones. A more familiar application is the Green Fluorescent Protein (GFP) found in some jellyfish, which is widely used as a genetic marker by scientists.
The function of luminescence in ctenophores is not yet known. Each species has a unique pattern, and they emit the full color spectrum. Isn’t that amazing? Check out this video to see these fascinating creatures in action!
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