It’s pretty well known that light has a direct correlation with the health of aquatic animals, including fish, shrimp, and snails.
But how does it affect corals? Will they grow differently when exposed to different light intensities and colors?
Since I asked myself this question quite often a few years ago, I decided to devote an entire article to this topic.
So, without further delay, let’s get started.
Does Light Affect Coral Growth?
Yes, light affects coral growth by enhancing calcification and providing nutrients through photosynthesis by zooxanthellae, but it needs to be controlled to avoid disruption of natural biological processes.
Corals look like plants. But the organisms are actually animals consisting of hundreds, possibly even thousands of soft-bodied coral polyps.
You can’t tell because these polyps are clumped together.[1] The limestone exoskeleton contributes to the wrong perception amateur aquarist have of corals.
They create the skeleton using calcium carbonate in a process called calcification.[2] But why does light matter to these creatures?
Ariel A Roth, Paul Y. Yahiku, Walter W. Cox, Venus E. Clausen, and Conrad D. Clausen (the University of Hawaii Press) revealed in a paper that light enhances calcification.[3]
But why? What kind of relationship does light have with Corals? Consider the following:
1. Zooxanthellae Need Light For Coral Symbiosis
Corals have a symbiotic relationship with zooxanthellae, the microorganisms found in a coral’s tissue.
Zooxanthellae are photosynthetic. They use light to provide the nutrients corals use for calcification.
The intensity and quantity of light do not matter as much as people assume where growth is concerned.
Miriam Schutter, Ronald Osinga, Max Janse, Johan A.J. Verreth, Rosa M. van der Ven, and Rene H. Wijffels performed a study that exposed corals to different light intensities and photoperiods.[4]
Their paper, published in the Cambridge University Press, revealed that an increase in the photoperiod (duration of exposure) and intensity did not change coral growth.
Therefore, you can’t necessarily boost zooxanthellae photosynthesis rates and coral growth by giving your reef tank more light.
In fact, the paper observed bleaching and death in corals exposed to too much light.
2. Creating A Day/Night Cycle Is Crucial For Corals
Light’s influence on a coral’s growth is most evident in coral reef formations on the coast.
The Florida Reef Tract (360 linear miles), the third largest of its kind in the world, is under threat because it borders densely populated urban centers.[5]
Urban centers are significant sources of light pollution. The light scatters through the atmosphere, invading terrestrial ecosystems and changing their natural light/dark cycles. This is especially true for corals in shallow waters.
Because sunshine and moonlight govern their biological processes, artificial light at night can disrupt coral reproduction, reducing their growth rate.
A paper published in Communications Biology (Tirza Doniger, Oren Levy, Yael Rosenberg) has predicted a global reef decline in the future.[6]
That will be due to light pollution that prevents corals from performing their natural cyclic behaviors.
3. Light Has A Direct Impact On The Coral’s Color
The light intensity and duration can influence a coral’s color.
As you probably know, intense sunlight kills corals in the wild because it forces the creatures to eject their zooxanthellae.
This sounds like an irrational response because corals cannot survive without zooxanthellae.
However, it makes more sense once you understand that zooxanthellae respond to intense light by generating superoxide radicals, which are toxic to corals.
The corals have no choice but to reduce their zooxanthellae population. This makes the corals lighter in color.
Corals at lower depths of the ocean are darker because they have denser zooxanthellae populations.
Those allow them to maintain optimal photosynthesis rates even when the water compromises their access to light by absorbing spectrums with longer wavelengths.
What Is The Best Light For Coral Growth?
Corals in the wild use the sun to photosynthesize.
Therefore, you wouldn’t be wrong in identifying the sun’s white light as the best light for coral growth.
Experts define PAR (Photosynthetically Active Radiation) as light whose wavelength ranges between 400 and 700nm.[7]
Sunlight ticks that box because it has all the colors, including:
- Violet (400 – 430nm)
- Blue (431 – 480nm)
- Green (511-530nm)
- Yellow (571 – 580nm)
- Orange (581- 600nm)
- Red (601 – 700nm)
A daylight bulb is more than adequate for your reef tank because it mimics the sun.
However, if you can only select one color, blue stands out because of its penetrative power.
The color is visible at depths exceeding 100m. Red, on the other hand, will disappear after 5m.
Blue has more energy. It can stimulate photosynthesis more efficiently than red, orange, yellow, and green.
But, from what I have seen, many aquarists use full spectrum LEDs as opposed to prioritizing one color.
Do All Corals Respond To Light The Same?
A coral’s response to different intensities and photoperiods will vary depending on the type and species of coral.
A study in ‘Estuarine, Coastal, and Shelf Science’ exposed Acropora millepora, Platygyra sinensis, and Pocillopora damicornis to different light intensities and photoperiods.[8]
Platygyra sinensis performed surprisingly well under every light intensity level it encountered. Or, at the very least, the coral survived.
However, the survival rates fell (20 to 80 percent) in the other two coral species once light intensity levels deviated from the ambient light conditions.
On the other hand, both Platygyra sinensis and Acropora millepora survived under every photoperiod level. Interestingly, the coral growth remained largely unchanged.
The only significant discovery was Platygyra sinensis’ tolerance for various light intensities and photoperiods.
The species is just as important to a coral’s response to the color. For instance, one study found that Stylophora pistillata thrived under LEDs that emphasized blue.[9]
Additionally, the species maximized its growth under a balanced LED spectrum that increased the red and reduced the blue light even though the irradiance was low.
Pocillopora damicornis did not fair that well under similar conditions.
All LED treatments produced negative growth rates, and eventually, the researchers observed tissue necrosis. They blamed this outcome partially on the limited water flow rate.
Montipora aequituberculata was the most impressive of the bunch, manifesting the highest growth rate at low irradiance. Porites cylindrica showed no growth even at the highest irradiance.
Experienced retailers won’t stop selling you corals. They will also recommend a suitable lighting system and schedule based on the coral species.
In the absence of such guidance, you can rely on online aquarium communities whose members are quite eager to share their knowledge.
For now, here are some corals I know that require low or high light intensities:
Corals that require high light:
- Staghorn coral (Acropora sp.)
- Thin finger coral (Montipora digitata)
- Bird’s nest coral (Seriatopora hystrix)
- Cauliflower coral (Pocillopora damicornis)
- Cat’s paw coral (Stylophora pistillata)
Corals that require moderate to low light:
- Plate coral (Fungia sp.)
- Lobed brain coral (Lobophyllia hemprichii)
- Leather coral (Sarcophyton sp.)
- Sun coral (Tubastraea sp.)
- Sunflower coral (Dendrophyllia sp.)
Can You Grow Corals With LED Lighting?
Yes, you can. LEDs are the most efficient option on the market.
First, they don’t waste power by overheating. LEDs don’t have a reputation for ruining a tank’s balance by making the water hot.
Secondly, you can adjust their brightness. This adds flexibility to your lighting schedule.
Rather than switching the lights on and off at the beginning and end of the day, you can gradually ramp up and down, giving the fish a chance to adjust to the changes in their environment.
Third, LEDs put all the colors at your fingertips. You can alter the spectrum to fit your coral type’s needs.
How Many Light Hours Do Corals Need?
As a general rule of thumb, corals need 8 to 12 hours of light.
If you’re determined to keep the lights on at night despite the potential side effects, use blue and red. These colors are less likely to disturb the fish.
However, it is better to leave the lights off during the night. Corals need at least six hours of darkness for proper calcification.
What Is The Easiest Way To Light A Coral Tank?
Without a doubt, the easiest way to do all of the above is with an automatic LED lighting device, which takes care of everything for you.
Without one, you may forget to turn the light on and off, potentially exposing your corals to inadequate amounts of light.
To overcome this, I personally use the Hygger 24/7 Lighting Aquarium Light (link to Amazon).
I chose it because it is very cheap and economical in electricity consumption. It is set to the following schedule by default, but you can play with it if you like:
| 8 am – 6 pm | White color |
| 6 pm – 10:50 pm | Blue color (imitating the moonlight) |
| 10:50 pm – 6 am | Lights are off |
| 6 am – 8 am | Orange color (imitating the sunrise) |
| 8 am – 6 pm | White color again, and so on |
Pro Tip: Feeling uncertain about how to light your coral tank? Don’t worry, I’ve got you covered with my ultimate guide on the topic.
Conclusions
If you’re in a hurry, here’s a quick rundown of the key points mentioned above:
- Light affects coral growth by enhancing calcification through the symbiotic relationship with zooxanthellae, which require light for nutrient production.
- A day/night cycle is essential for corals, and artificial light at night or light pollution can disrupt reproduction and reduce growth, potentially leading to global reef decline.
- Light influences coral color through intensity and duration, and deeper corals are darker due to denser zooxanthellae populations.
- Sunlight’s white light with all colors in the PAR range is best for coral growth, with blue light being the most efficient for photosynthesis compared to red, orange, yellow, and green.
- Coral species have varying tolerance levels for light intensities and photoperiods, and their response to different lighting conditions will differ.
References
- https://www.anthropocenemagazine.org/2019/10/light-pollution-coral-reefs/
- https://link.springer.com/referenceworkentry/10.1007/978-90-481-2639-2_10
- https://scholarspace.manoa.hawaii.edu/server/api/core/bitstreams/7d267d61-4904-44f5-9188-3987124f692a/content
- https://www.cambridge.org/core/journals/journal-of-the-marine-biological-association-of-the-united-kingdom/article/abs/light-intensity-photoperiod-duration-daily-light-flux-and-coral-growth-of-galaxea-fascicularis-in-an-aquarium-setting-a-matter-of-photons/CC641AF80B0994F8940155BDFC7EBC99
- https://www.darksky.org/artificial-light-impacting-coral-reef-species/
- https://www.nature.com/articles/s42003-019-0548-6
- https://www.researchgate.net/publication/266422526_The_role_of_light_in_coral_physiology_and_its_implications_for_coral_husbandry
- https://www.sciencedirect.com/science/article/pii/S0272771419304652
- https://reefs.com/magazine/coral-growth-under-light-emitting-diode-and-light-emitting-plasma-a-cross-family-comparison/