How do Jellyfish use Bioluminescence? What is its importance in Jellyfish?

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A jellyfish is not a true fish. It is an invertebrate. It’s called jellyfish because it is made up of a jelly-like substance.

The various species of jellyfish live in coastal waters alone or in large numbers. They can be either floating with water currents or waves or swimming freely at deep oceans where sunlight couldn’t even penetrate.

They are soft animals that can produce glowing light from their body which is actually due to the chemical reaction that is happening metabolically within their cells and tissues. This type of light is also termed bioluminescence.

Bioluminescence in jellyfishes is used by them for self-defense purposes, attract and lure their prey, camouflage to confuse their predators, and also as a way to release their excessive chemical energy in the form of light and heat.

In water, when touched by predators that start to suddenly glow thus fearing them and letting them move away. With their light, they also mimic those of the small planktons thus confusing their predator.

Here in this post, we’ll know more about the bioluminescence property and its use in jellyfishes elaborately. So, just keep reading…

Glowing Jellyfish due to Bioluminescence
Glowing Jellyfish due to Bioluminescence

What exactly is Bioluminescence?

Bioluminescence is the phenomenon of the emission of bright glowing light from the body of biological organisms due to the various chemical metabolic reactions happening inside the cells. This type of property is very popular amongst marine organisms.

Bioluminescence is a “cold light”, meaning that less than 20% of the light generates thermal radiation or heat.

The oxidation reaction is widely seen during the process of emission of biological light. Bioluminescence generally involves a light-emitting molecule luciferin and an enzyme luciferase respectively.

Bioluminescence occurs only when the enzyme luciferase catalyzes the oxidation of the luciferin molecule.

In some species, the luciferase requires other molecules like calcium or magnesium ions, and sometimes also the energy-carrying molecule Adenosine triphosphate (ATP) to cause bioluminescence.

One of the most popular bioluminescent organisms that we are talking about here in this post is the jellyfish. Not only jellyfish, but comb jellies produce bright flashes to confuse a predator as well.

Apart from the jellyfishes, other colonial hydrozoans can also produce a chain of bright glowing light or release thousands of glowing particles into the water. These glowing particles mimic small plankton to confuse their predators.

Some of the most common functions of bioluminescence in the oceans are for defense against predators or to find or attract prey.

In the deep ocean, where sunlight is dim or absent, more than 90% of the marine animals are bioluminescent.


What causes Jellyfish to glow? How does bioluminescence in jellyfish work?

Not all jellyfishes glow. It has been estimated that only about 50% of the total jellyfish species are bioluminescent in nature. Some of these remain in the deep darker parts of the ocean water zone.

Jellyfishes are bioluminescent and they produce light by a chemical reaction happening within their bodies. Their body contains the light-emitting molecule luciferin and an enzyme luciferase along with other essential co-factors.

The oxygen in the body of the jellyfish plays a key role here. The molecule luciferin acts as the substrate whereas the luciferase acts as an enzyme.

In biochemistry, the substrate is a molecule upon which an enzyme acts. Therefore, the enzyme luciferase accelerates the chemical reactions involving the substrate luciferin.

As a result, luciferase reacts with oxygen in the presence of enzyme luciferase causing an oxidation chemical reaction. This results in the formation of oxyluciferin which is a byproduct along with light from the body of the jellyfish.

In some hydrozoan jellyfish species like the Aequorea victoria, uses the photoprotein Aequorin as an enzyme instead of luciferase.

Aequorin by itself generates blue light. Aequorin protein needs calcium ions as cofactors as these are only the calcium-activated photoproteins.

Therefore in Aequorea victoria like species, luciferase reacts with oxygen in the presence of the enzyme Aequorin along with the cofactor Calcium to form oxyluciferin by an oxidation reaction. Later on, oxyluciferin recombines with aequorin to produce bright blue light.

In some cases, Aequorea victoria also produces a bit of green light. It’s because some of the blue light released by Aequorin in contact with calcium ions is absorbed by a green fluorescent protein, which in turn releases green light in a process called resonant energy transfer.

That’s what causes Jellyfish to glow and the bioluminescence to happen.


How do Jellyfish use Bioluminescence? – (Uses of Bioluminescence in Jellyfish)

1. For self-defense against predators

Yes, one of the most prominent uses of bioluminescence in jellyfish is for self-defense purposes against their predators.

Jellyfish such as Comb Jellies protect themselves by giving off a bright bioluminescent glow that scares and often confuses any predators that might come their way.

Some species of Siphonophores that include many true jellyfishes can release thousands of bright glowing particles into the water as a mimic of small plankton to confuse their predators.

It has also been seen that many species can also shine when they detect a predator, possibly making the predator itself more vulnerable by attracting the attention of predators from higher trophic levels.

It has also been examined that the bioluminescence in jellyfishes is used predominantly as a form of communication between individuals, and can be used for defense, offense, and intraspecific communication as well. The mechanism of intraspecific communication is still not so cleared due to the lack of proper evidence.

The light produced by Comb jellies, for example, can be used to both confuse and attract predators.

2. To lure and attract their prey

In the deep sea oceans, more commonly you will find that the glow due to bioluminescence lures and attracts prey by mimicking some other forms.

Some jellyfishes can brightly glow and release various glowing substances in the surrounding water that mimics other phytoplanktons or zooplanktons. These attract prey thinking there’s food for them thus, helping the jellyfishes to feed easily on these fooled prey.

In simple terms, bioluminescence can act as a torch that functions as a glowing lure for the prey to attract them to within striking distance.

Some species have also been recorded to suddenly flash a bright light to startle and shock their prey as soon as they have touched the jellyfish, thus making it easy to hold on and feed their prey.

3. They can exclusively camouflage in deep water

Bioluminescence helps the organism blend with its surroundings and camouflage to confuse both its prey and the predators.

Camouflage in jellyfishes better hides the organism and mimics it due to a specific combination of coloration, or illumination by making the differentiation between the organism and its surroundings hard to notice, or by disguising them as something else.

Camouflage helps them to get rid of predators and makes it super easy for them to feed on their prey.

They not only have adapted their body color to camouflage in the darkness, but also their bioluminescence has helped them to pretty much match with the surrounding in the deep-sea zones.

Some deep-sea jellyfishes and comb jellies glow with a bright red or orange color. The camouflage here is because the red color cannot be seen in dark water (deeper than 200 meters), so there’s no greater protection from black than being in the red.

Some deep-sea jellies just have dark red guts, which possibly makes the larger predators think of the jellyfish as a large animal with big eyes.

4. They release their excessive chemical energy in the form of light and heat energy

Researchers even say that jellyfish are able to release their excessive chemical energy in the form of light as a by-product. This may be a way to get rid of the excessive chemical energy which their body doesn’t need in the form of light and heat energy.

Bioluminescence is a “cold light”, meaning that less than 20% of the light generates thermal radiation or heat. That less than 20% is what is given out in the form of a little heat energy to regulate the body temperature of the jellyfish.

And, the rest of the chemical energies that have been resulted from the oxidation reaction between luciferin and oxygen in the presence of enzymes like luciferase or other photoproteins is given out as light energy.

The release of excessive chemical energy in the form of light and heat energy acts to balance the thermodynamics, temperature-dependent effects, pressure, and also in maintaining the equilibrium of the biological body.


Where do bioluminescent jellyfish live?

The bioluminescent jellyfishes live and remain in single or in a group of many throughout the water column, from the surface to the seafloor, from near the coast to the open ocean.

If you go out near the coastline, you will find many bioluminescent jellyfishes glowing with full light while floating on the upper surface of the water.

And in the deep sea, the availability of the many bioluminescent jellyfishes is extremely common and widely seen by deep water divers.

Most bioluminescent ones live throughout the ocean’s depths, but most exist in one particular twilight zone of the ocean that ranges between 660 feet (201 meters) to about 3,300 feet (1,006 meters) deep.

The bioluminescent jellyfishes can only be seen in the ocean, and no evidence of such bioluminescence has been recorded in lakes and rivers.

The magical views of bioluminescence in water are never a guarantee, but if you know where to look, you can greatly increase your odds of viewing the elusive, magical illumination of the glowing biological light.

Some of the places like the Toyama Bay, Japan; Merritt Island, Florida; Maldives Islands, etc. are well-known spots to see not only bioluminescent jellyfishes but also other bioluminescent marine creatures.

One of the most popular ones is the Aequorea victoria, which is sometimes called the crystal jellyfish, which is a bioluminescent hydrozoan jellyfish, or hydromedusa, that is found off the west coast of North America.

Another one is the Alarm jellyfish (Atolla wyvillei) that flashes an amazing light show when caught in the clutches of a predator. Like many species of mid-water animals, it is deep red in color. They can be found all over the globe in the deep ocean.

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