Coral Coloration and What Variables Affect Their Color

Coral coloration is such a big issue to anyone in the marine reef aquarium hobby. We want the brightest and most vibrant colors associated with our corals. One of the main reasons for the desirable coloration of our colors, apart from the aesthetically pleasing look, is the fact that for the most part coral health is employed to categorize the over all health of the particular coral as well as being a good indicator of lighting and water parameter conditions, both good and bad.

As for determining color of corals it is safe to assume that their is more than one underlying factor responsible for the overall color of our corals. Words like, UV rays, kelvin, light spectrum, light intensity, dissolved organics, excessive nutrient concentration and supplement addition such as iodine are all viable components in the overall color representation provided to us by our corals.

Corals react to various stimuli and environmental conditions that they encounter, mainly through the use of specialized cells and pigments. Zooxanthellae are brownish/green dinoflagellates containing chlorophyll that provide corals beneficial nutrients through the process of photosynthesis. Zooxanthellae are also known as specialized light sensitive cells and can increase or decrease based on available light intensities. Zooxanthellae combined with primary and auxiliary pigments are what gives coral their color. In addition to the pigments giving the corals tissue it vibrant colors, these pigments are essential to the protection of the corals delicate tissue from harmful and damaging UV rays of the sun and artificial light sources associated with the lights above our aquariums.

If a coral receives too much light, two things can happen. Zooxanthellae will be expelled, or chlorophyll production will be reduced. These alterations can mean the difference between life and death of the coral. Too much light means an overabundance of oxygen(super oxide radicals) that zooxanthellae must work harder at to photosynthesize the intense light thus creating higher levels of oxygen in the corals tissue that can be toxic at high concentrations.

At the other end of the spectrum a coral or clam can receive light that is to low, therefore the population of zooxanthellae will need to increase along with available chlorophyll in efforts to capture more light .

So in essence chlorophyll and zooxanthellae are responsible to the coloration of symbiotic corals depending on the amount of these in the particular coral at a given time. Golden yellow to brown colors associated with zooxanthellae will either cause the coral to be darker or lighter in color based on available light. If the wrong light parameters are not met, then bleaching will occur causing the coral to, often times, become white as is evident by the corals expelling of its beneficial zooxanthellae. In time if these conditions are not rectified, the coral will die!

The different kelvin(light spectrum) or colors of the bulb has a profound effect on the color of the coral as well. The lower kelvin bulbs in the 6800k range will cast a warmer yellowish red color while the water with a bulb color that is cooler in temperature and say 20000k will be viewed as a crisp blueish white glow. Actinic lighting which comes across as a purple/blue hue can cause certain corals and fish to glow and fluoresce that would not be otherwise evident under daylight spectrum lighting in the 10000k spectrum and less. This may not be a favorably acceptable bulb coloration to some aquarists due to the bluer water coloration evident in deeper reef areas of our oceans. The bulb color definitely can alter the color of coral from one tank to another, thus, a coral that looks one color in one persons tank can look very different if the same coral is viewed under a different light bulb scheme.

Ultra-violet radiation can be of significant importance to a corals health and growth, but it can also harm and even kill a coral due to the intensity of the UV-A and UV-B waves provided by the sun and also metal halide lighting especially. Protective primary and auxiliary pigments are found on many corals, such as Acropora, Pocillipora and Zoanthids. Due to their often times residing out of water at low tide, these corals must rely on acceptable means of protection while exposed to the extreme heat, suns rays and possibility of drying out. Forming a mucus, excreting water periodically and development of protective pigments often blue, pink and purple in color are ways that coral can thrive in these extreme conditions.

These protective pigments are responsible for giving a coral a different appearance than would otherwise be evident. A coral that has lost its protective pigments due to shipping or subdued lighting, will look noticeably different than if it were maintained under optional conditions. Often times these bright colors can adjust to lower UV wave lengths and conditions in a captive environment, though may seem different that if they were seen in the wild or other intense light scenarios.

The maintenance of a clean tank meaning clean protective glass shield and tank cover from algae or salt creep can ultimately alter the light intensity and colors of your live stock in your tank. A religious regimen of proper and thorough cleaning weekly can help you to capture the full, vibrant beauty that can be evident in your tank. The reduction of excess nutrients, toxins, tannins and yellowing agents such as "Glebstoff" can also play a major role in the actual color of your coral. Proper and efficient skimming and carbon dosing combined with weekly water changes, ideal feeding schedule and bioload will help to ensure that your tank will be crystal clear and pristine and afford your corals and clams of really exemplifying their true beauty and glamor for you to enjoy time and time again.