How Coral Fluorescence Works

Coral fluorescence is a common phenomenon among corals and other marine animals. Fluorescen occurs only when the target is stimulated by a certain type of light. A coral may appear to glow in shades of green, red or blue under certain light wavelengths. Corals fluorescen when certain pigments within them respond to short wavelength light, such as blue light, emitting light of shorter wavelengths, such as green, red, or yellow. Corals produce proteins that fluorescen (FPs), while hosting symbionts known as zooxanthellae. FPs are utilized to re-emit light.

Fluorescence is the process by which energy is absorbed by a substance at one wavelength, and then released at a shorter wavelength.  Absorption occurs when a photon (light particle) excites an electron causing it to move from a stable state (ground state) to a higher state (unstable state). Excited electrons tend to regain its stable state. In order to do that, they have to emit a photon of light, losing some energy in the process. The light emitted is usually perceived at lower wavelengths, which is perceived as color.

Fluorescence is short lived. Once the source of excitation is absent, fluorescence tends to decay in a fraction of a second. The ratio of emitted photons to photons absorbed by a pigment is called the Fluorescence Quantum Yield. The higher the fluorescence quantum yield, the more efficiently the pigment becomes at absorbing fluorescence light. Quantum yields may vary significantly, and could be due to a variety of factors, including concentration, purity, maturation conditions and protein source.

Some of the fluorescent pigments in corals stem from the green fluorescent protein (GFP) found in a number of marine animals. Green is the most common fluorescence color, although, fluorescence may reveal other colors in the red, orange and yellow spectrum. Corals produce a variety of fluorescent proteins (FPs), including some that do not emit fluorescence in the visible spectrum known as pocilloporins (GFP-like proteins). FPs contribute to the diversity of colors seen in corals. Fluorescent protein, including cyan (CyFP), green (GPF), yellow (YFP) and red (RFP) are thought to play a role in the protection of corals from sunlight radiation.

In 2008 Martin Chalfie, Osamu Shimomura and Roger Y. Tsien were awarded the Nobel Prize in chemistry for their discovery and development of the green fluorescent protein (GFP). While studying a glowing jellyfish in the early 1960´s, Osamu Shimomura isolated a bioluminescent protein giving off blue light. He found in later studies that a second jellyfish re-emitted green light when absorbing blue light. The ability to process blue light into green light was found to be integral to the basic structure of the jellyfish without the need of additional factors. Martin Chalfie proved the value of GFP in various biological processes. Roger Y. Tsien made research that led to the understanding of how GFP fluorescence works.

Fluorescent proteins, such as GFP and GFP-like fluorescent proteins from Anthozoa species. have allowed the direct genetic encoding of fluorescence, permitting their utilization in molecular and cell biology. GFP from the jellyfish and similar proteins from diverse marine animals are utilized as genetically fluorescent labels. In present days, laboratories have focused their research efforts in the identification and development of fluorescent proteins with unusual characteristics and enriched properties as a means to gain insights into the structural organization and dynamic processes inside cells and organisms.

The phenomenon of coral fluorescence is an experience worth seeing.  Through fluorescence, aquarists around the world are able to discover life forms they didn´t know existed. To experience fluorescence in aquaria, or coral reefs, equipment, such as a source of light and an excitation filter to block all colors except blue light are needed. There are a number of hypothesis developed regarding the function of FPs in corals. Some of the most general hypothesis state that FPs may provide photoprotection. Marine biologists say they may allow the process of photosynthesis in the absence of light.