Why is Light so Important to Corals?

Corals get energy through photosynthesis as well as by capturing prey with their polyps. Light is crucial to all photosynthetic corals as photosynthesis is the primary way that corals derive their energy. We can think of photosynthesis as the corals 3 meals a day and the food they grab with their polyps as their supplemental vitamins that give their growth and health an added edge.  The energy corals get from light is created by photosynthetic algae which reside in the corals tissue and are called zooxanthellae or Zoox for short.  A good portion of the corals energy goes into building a skeleton which the tissue and Zoox live on and within.  As this skeleton grows, it helps the corals not only reach upwards towards the light, but also allows them to compete with each other for the available light similar to how trees grow in a forest.

How Many Hours of Daylight do Captive Corals Need?

If we use the natural world as a model for daylight length for our corals in captivity, then one can pretty quickly come to the conclusion that these conditions vary greatly in the worlds oceans.  The roughly 400 species of coral that are in the worlds’ oceans reside in many different micro habitats and thus are subject to different lighting based on their latitude, depth, and the water quality that they live in. So, how do we determine what effects light duration has on our tanks?  The easy way is to assume mother nature has finely tuned our oceans over millions of years to provide corals with their ideal growth conditions.  Given this a light duration of say, 9-13 hours would seem to be a good rule of thumb with certain considerations for the type of lighting one is using as well as what type of habitat the corals we keep have come from.

How to Control Day Length Over Your Tank.

In the 14 or so years that I have been keeping corals, the equipment that we use to control these fragile environments has become automated more and more every year.  Back in the 90’s folks pretty much relied on analog timers or surge strips with timers to control when lighting came on and went off.  Today these same methods are still used by many for a no frills way of simplifying the turning of lights ON and OFF.  In the last few years however, a good percentage of reef hobbyists have switched to using controllers such as those made by Neptune Systems and Digital Aquatics to control not only their lighting, but many other tasks for their reef tanks. These timers allow the synchronizing of your light cycles to the same day by day conditions that would be found at a given latitude on a reef.  More simply, they also offer the ability to just turn the lights on and off at certain times of the day or night.

As we see, there are many variables that can affect coral growth even within the one parameter of lighting.  As most reef keepers know, these variables have to be dialed in slowly on your tank so as to make sure you have adequate lighting for all the inhabitants without scorching them or depriving them of light.  This fine balance is best achieved through close observation of your corals and by changing only one variable at a time.

How many hours of daylight and night do you use on your tank?

What have you observed as you change the daylight?

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