Jellyfish generally cannot change colors rapidly for camouflage or communication, unlike animals such as octopuses or chameleons. Their coloration is complex, stemming from fixed biological components that interact with light. While the jellyfish does not actively control a swift color change, its appearance can be dynamic and variable.
How Jellyfish Get Their Color
A jellyfish’s inherent color results from a combination of pigments and specialized proteins fixed within its tissues. Visible color often comes from carotenoid pigments absorbed through their diet of plankton and small crustaceans. For instance, consuming large quantities of larval crustaceans can impart a pink or purple tint to the bell of translucent species like the Moon Jellyfish.
Visually dramatic effects often arise from fluorescent and bioluminescent proteins. Green Fluorescent Protein (GFP), initially discovered in the Aequorea victoria species, is a prime example of this mechanism. This protein absorbs high-energy light, typically in the blue or ultraviolet spectrum, and then re-emits it as a lower-energy green light, causing the jellyfish to glow under certain conditions.
Bioluminescence is a separate process where light is chemically generated by the organism itself, requiring no external light source. This reaction involves a light-emitting molecule, luciferin, which is oxidized by an enzyme called luciferase, or in some cases, by calcium-activated photoproteins like aequorin. These reactions produce light, often a blue or blue-green color, which is a fixed biological trait rather than a controllable color palette.
Distinguishing Active Change from Dynamic Display
Rapid color shifting requires specialized, muscle-controlled organs that jellyfish lack. Cephalopods, such as squid and cuttlefish, utilize complex skin organs called chromatophores, iridophores, and leucophores to instantly expand or contract pigment sacs and reflect light. Jellyfish lack this sophisticated cellular machinery, meaning they cannot voluntarily change their body’s base color.
The visual display of a jellyfish can appear dynamic due to passive mechanisms involving movement and light interaction. The rhythmic pulsing of the bell, a common form of locomotion in scyphozoan jellyfish, constantly changes the angle at which light reflects off their translucent bodies. This motion creates a flashing or shimmering effect that can be mistaken for an active color change.
Ctenophores, commonly known as comb jellies, provide a striking example of this passive display. These organisms use eight rows of fused cilia, called comb rows, to propel themselves. As these rows beat, they cause light to diffract, splitting the ambient light into a shimmering, moving rainbow spectrum. This iridescent effect is purely an optical phenomenon caused by the physical movement of the cilia, not a physiological color shift. Some deep-sea jellyfish employ bioluminescence as a “burglar alarm” defense, where a flash of light attracts a larger predator, creating a rapid, controlled light display rather than a shift in body color.
External Factors Affecting Color Appearance
A jellyfish’s appearance can undergo slow, long-term shifts influenced by external environmental factors. The accumulation of dietary pigments is a primary influence, as the color of ingested prey slowly integrates into the organism’s tissues over time. This means populations feeding heavily on one type of pigmented plankton may appear different from another population in a separate location.
A jellyfish’s age can also affect its visible color due to the concentration of proteins or pigments. Some species exhibit a distinct color change as they mature; for instance, the Purple Jellyfish is often a lighter pink shade when young before developing a deeper purple hue later in life. These shifts are physiological changes occurring over the lifespan, not rapid, intentional color adjustments.
Light conditions in the water column dictate how a jellyfish’s proteins are perceived by an observer. Fluorescent proteins require light of a specific wavelength to become excited and emit their color. In the deep ocean, where only blue light penetrates, species are often pigmented red or orange. Since red light is absorbed quickly by water, these colors appear black in the darkness, providing an effective form of camouflage.