How important are UV rays to the color of corals

[thincat]

Okay, I've been thinking about this for a while and need some input.
The question is, How much do UV rays play in the color of corals.

 

[redneckgearhead]

wouldnt uv rays kill the corals?

 

[ChizerBunoi]

I don't know about UV rays per say but I can tell you my observations based on kelvin temperature. The 6700K - 14000K are more of a daylight spectrum and don't show the colors off properly. These temperatures are very pleasing to the eye over all and are very bright.

If you keep any deeply colorful corals (zoanthids, palythoas, ricordia, etc..) then you want to add more actinics to balance it out. At 20000K, it gives you a nice look but not as nice as being able to simulate dawn and dusk with multiple bulbs.

A mh fixture will give you higher uv output compared to other lighting fixtures. This is why the daylight bulbs appears to cause the bleaching out of corals. The intensity is too strong. We also need to have a uv protected coating/glass to filter out the harmful uv rays.

The deeper the tank is, the more uv rays will be filtered out of the spectrum (through the water) as it reaches the bottom of the tank. The corals that are higher up and closer to the light will produce nicer colors compared to the bottom of the tank. They will brighten up as a protection from the uv rays striking them. Look at a shallow reef in the ocean compared to the deeper end of things.

Zoanthid corals are known to produce nicer color pigments as a protection against these uv rays.

So going back to kelvin temperature, the higher intensity daylight temperatures (simulate afternoon time) will appear to bleach out the corals. But when you view it under an actinic light (higher in the spectrum with more colors), it is more colorful.

Okay, I am rambling on and don't even think I'm answering your question or am on topic. I thought I take a stab at this but am probably totally off.

 

[Innovator]

Chizer has the general scope. Kelvin is merely the temperature (color) scale of light in degrees. The higher the K temperature rating the bluer the bulb appearance and the greater depth of color conformity. The actual usable energy for photosynthesizing is PAR (Photosynthetically Active Radiation), thus once the saturation of usable light has exceeded its threshold the coral can no longer increase photosynthesis. Generally, excessive light intensity will compromise coral processing, but corals have the ability to produce a pigmentation that acts as a sunscreen to retard UV inhibiting rays. These proteins are believed responsible for the fluorescing of coral species, but does not necessarily dictate whether or not a coral is receiving the proper constituents to maintain health.

Hopefully I am not too far off the barren path in accuracy and if so, well, be gently...I'm tired

 

[thincat]

Thanks, so corals produce a film to protect themselves from UV, but how is this suppose to add color to them. I was thinking in terms of a prizm much like the cuts in a diamond. the diamond looks clear, but if a light goes through them they shine like a rainbow....Wow, am I that far off base.....time for my meds lol

 

[redneckgearhead]

Most UV rays are in a spectrum we can not see so Im not sure how that would affect the color of the coral since color is just the color of light reflected off of an object.

 

[mr_X]

i was under the impression UV rays were bad for everything. this is why we shield our eyes, and our corals from them. all of your mogul halide lamps have UV shields and HQIs have a flat piece of glass that goes between the bulb and everything else. plants develop pigments to shield themselves from it.
also, it's my understanding that UV rays are not used in photosynthesis. only visible light rays are used.

 

[cmor1701d]

From LiveAquaria...


Color change due to UV light
In nature, ultraviolet light waves (UV-A and UV-B) penetrate the ocean's surface but are filtered out as the light travels through the water. Both UV-A and UV-B light waves have been found to cause destruction of DNA and RNA within coral tissue. In response, many corals have made adaptations to reduce the effects of these harmful rays. These corals developed protective pigments that are often blue, purple, or pink in color. Most corals that contain these pigments come from shallow waters where the amount of UV-A and UV-B light is higher than in deeper areas of the reef.
In home reef aquariums that rely on metal halide lighting, it is important to protect corals from UV light. Coral without these protective pigments as well as shallow water corals that may have lost their pigments during transportation are especially susceptible to the effects of UV light.
...It is not uncommon for corals with these bright colors to adjust to the lower UV-A and UV-B conditions found within home aquariums. The loss of colorful pigmentation is not necessarily a sign of an unhealthy coral - it is simply a normal coral adjusting to its new environment.

And from Science Now...
Coral Reefs Act Like Sunscreen

 

[thincat]

So what can we do in our home Aquraium to prevent our corals from loosing it's color pigment? It seems that alot of corals lose their color after we buy them from the LFS. I have heard the statement saying it's because our light level is diffenent from the LFS. Is that the case or are they loosing their UV protection? If they are loosing their UV protection then we, home aquarium keeper, should find a way to add some UV to our lights that shine into our AQ. This may be very hard since we do not know at what depth our corals came from.

 

[mr_X]

i truly think that we have more light on these corals than they get in the wild. anyone that has ever went on a dive out at any reef will attest to the fact that it's not nearly as bright 25-30 feet under sea water as it is under our lighting at 24".
this is why people "discover" corals that are not divers. the collectors collect them as somewhat colored or even browned corals, and bring them to the wholesalers who sell them and so on...until the guy with the right lighting gets them and colors them up.

 

[cmor1701d]

Ariund Fiji and many other islands corals grow in 15 feet or less of water and some are exposed at low tides for several hours. These corals get quite a bit of light and UV.

Doug, how about a dive trip to the Pacifc next year????