Excess Light Doesn't Cause Coral Bleaching

My take on this is our systems usually don't have as low a level of DOC in the ocean. We now pollution is a cause of bleaching along with other stress. We then add more radiance than is necessary for the corals' survival to the equation. The final leg of the equation would be temperature to throw the coral over the edge. The temperatures we keep the tanks at are most likely too high for the coral to deal with the stress from the DOC and light level.

Light is getting the rap for the bleaching because we try to understand how it works but rarely can figure out enough to be confident. Add in more is better as a common disease of husbandry when it comes to light and we have our "culprit".

 

How are you coming to that conclusion? It's not easy to measure DOC and not many people have tested it in our tanks. Recently this was done though and the result was that DOC levels, in a well filtered aquarium, are lower than the ocean. There are means by which you can get to or above ocean levels, but it appears difficult to get higher than ocean levels. Of course low DOC could be a stressor too and there could be more swings in DOC, which could be stressful etc..

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Agree, there are almost certainly more stressors and pollution in our tanks than the ocean. Light is a stressor and I think in many cases, can definitely push the balance over the edge.

In many cases, although, our tanks are cold compared to the ocean.
I think most people try to keep their tanks around 78 deg F, really that's already about 4-6 deg F below reef averages already. Maybe low temp is a stressor? I'm not saying that low temp is a stressor BTW, I doubt that; just using the example as food for thought.

I don't really agree with Dr. Shimek's conclusion, but he does summarize the data well here:
Aquarium Frontiers On-Line: November 1997: Feature

Definitely, nothing wrong with moderation; many corals don't "need" as much light as we try to give them. Add in other stressors, and the light can appear to be the "culprit". In reality though, it's more appropriate to say that the main culprit is that our tanks aren't perfect recreations of the ocean.

 

Interesting thread IMHO

my personal experience of bleaching has been limited
I recall only 3 cases
all 3 cases involved LPS corals (green coloured LPS in all 3 cases)

all 3 where transfers from either a LFS in which one had been kept under less light or from other tanks I had, which again involved them being expossed rather quickly to more light than they had become accustomed to

all 3 cases involved the green colouration fading, and in the case of the Elegance coral, it became almost ghostly white

all 3 corals recovered after a period of being adjusted to the new conditions

what I find most interesting is that people have different manners of keeping the same species of corals - we have fine looking and colourful SPS corals under 4 x T5s and we have fine looking and colourfull SPS corals under 400 watt halides ( and in many cases the tank depths are similar so its not always a case of the halide tank being deeper than the T5 tank. Now the corals under the 400 watt halides may well be in more light than they actually require, but that in itself does not always lead to bleaching )

the above do indicate to me that there is a valid case for other stressors having the final say as to whether the coral bleaches or not
because if it was lighting alone, we would see more of these cases in the heavier lit set ups and it seems to me that is not the case

 

This just seems to be a case in which correlation was mistaken for causation which is easy to do in the limited samples we "test" things in.

You guys scienced this thread up so much that I can't tell who's thinks what! I never thought this thread would get so much good information out there. I thought it would just be a, "my coral did this," "well my coral did that," type of thread. Thank you for bringing the real knowledge to the table!

 

Sorry to bump an old thread but this is really good information. Thanks everyone for providing it. I have a coral frag that was red when purchased and is now a bright pink. This thread has helped me understand the light portion of the formula. I was worried I had increased the light too quickly for it but it appears other factors are at play as well.

 

While there may be other stressors at play, the rapid increase in lighting may be the "last straw". I would suggest placing the coral lower in your tank, or reduce the light intensity or duration until it improves.