Jellyfish glow in the dark thanks to bioluminescence produced by specialized cells called photocytes. This bioluminescence helps them survive by attracting their prey, defending against predators, and communicating with other individuals of the same species.
The bioluminescence of jellyfish comes from chemical reactions carried out by specialized cells located in their bodies. Some jellyfish directly produce light thanks to a protein called aequorin, which can emit a flash of light when it comes into contact with calcium. Others release a luminescent substance through an enzyme known as luciferase, reacting with a molecule called luciferin. This bluish or greenish light allows them to effectively survive in the dark ocean depths.
The bioluminescence of jellyfish relies on a chemical reaction between a specific protein called luciferin and an enzyme, luciferase. When these two substances meet in the presence of oxygen, it triggers a special chemical reaction that releases energy in the form of light. It is efficient because the process generates very little heat, which is referred to as "cold" light. Some jellyfish also possess a specific protein, green fluorescent protein (GFP), which absorbs the light emitted by the chemical reaction and re-emits it in a different color, usually a bright green. In fact, this specific molecule, originally extracted from a jellyfish, is now widely used by scientists to observe cells under a microscope!
Jellyfish use their light for several very concrete reasons in their underwater daily life. First, in terms of survival, producing a glow allows them to defend themselves against predators. A sudden burst of light can surprise or temporarily blind a potential predator, giving the jellyfish time to escape. Some jellyfish even release glowing pieces that serve as decoys: the attacker focuses on the shiny fragment while the jellyfish discreetly slips away elsewhere.
For reproduction, light also plays a role. It helps attract partners during the breeding season, facilitating encounters and allowing jellyfish to gather during nocturnal mating events. Through this bioluminescence, jellyfish increase their chances of meeting, improve their reproductive success, and pass these astonishing luminous abilities on to future generations.
In jellyfish, light is a very useful tool for escaping from certain predators or, conversely, for better attracting their prey. Some jellyfish suddenly create flashes of light when they feel threatened, in order to surprise or dazzle their aggressor. This moment of confusion then offers them a valuable chance to get away quickly. Other species play a slightly different trick: they attract curious or naive small prey with their soft and fascinating glow, which approach recklessly only to end up in their tentacles. In any case, bioluminescence is a true survival strategy for them, as cunning as it is effective.
Not all jellyfish are bioluminescent: only certain species that primarily inhabit deep waters use this light-emitting ability to communicate and survive in dark environments.
The bioluminescence of jellyfish produces a cold light: unlike traditional artificial lighting, their light generates almost no heat, thus preventing them from wasting precious vital energy.
Bioluminescence in jellyfish sometimes serves as a light alarm: when a jellyfish is attacked, it emits light to attract a larger predator that might chase away the initial aggressor.
Scientists are studying bioluminescent jellyfish in the hope of applying their knowledge to medicine, particularly in the development of new diagnostic tools to detect certain types of cancer or to observe brain function.
Blue or green light travels better through seawater, allowing for the effective attraction of prey or the deterrence of predators, even in dark and deep environments.
No, most jellyfish only glow when they are disturbed, threatened, or actively hunting. The emitted light is usually temporary and corresponds to a specific reaction.
In certain regions and conditions (dark night, low light pollution, significant proliferation), it is indeed possible to observe this phenomenon near the surface of the oceans.
Yes, the bioluminescence of jellyfish is already being studied in medical biotechnology to visualize cellular processes, develop biological markers, and create innovative diagnostic tools.
No, not all jellyfish are bioluminescent. Only certain species have specialized cells capable of producing light.
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