Why do bleached coral turn white?

OK coral bleaching is the expelling of zooxanthellae.

If high nutrient levels cause the zooxanthella levels in the coral to rise, causing the coral to take on a brownish color. This causes the natural desirable color(caused by proteins) of the corals to be covered up.

Why do these natural desirable colors disappear instead of getting stronger after bleaching? I understand zeovits zeospur forces a coral to expel zooxanthellae there by enhancing coloration, what else happens in bleaching?

 

what are the "natural desirable colors"?

 

the colors you want in your corals, the ones that are visible when corals aren't browned out.

 

the zooxanthella are the desired colors. if they leave, you are left with no colors thus the "bleached" corals.

 

Thats a myth, the zooxanthella are brown, they are not the desireable colors. That is why high nutrient levels cause corals to turn brown.

 

Here is some info about pigments SAY
Feature Article: Coral Coloration: Fluorescence: Part 1 | Advanced Aquarist's Online Magazine

also I was wrong there is one sorta desirable color derived from zooxanthellae, that is a non flourscent red color like cyano's.

 

I believe that bleaching is for the exact opposite reasons for brown outs
brown outs as you say occur when nutrient levels are very high and thus the Zoos multiply masking the corals colours

bleaching or white outs I believe occur when nutrients are low and lighting is intense and light shock causes the Zoos to vacate en mass causing the coral to become white

I have read that some aquaculturing facilities , encourage this because the natural colour of the coral, for example a purple, looks much better when developing on a white base than it does when it starts re claiming a brown base

my understanding was that they basically light shock the corals into causing this white out, in low nutrient systems so that the number of Zoos on the corals where low anyway
and thus not out competing with the coral for the honor of providing the nutrients required


Steve

 

I have been lead to believe the most colorful pigments in a coral don't come from the zooxanthellae.
Mass zooxanthellae cover up those pigments and make the coral brown.

So based on that:
When a coral expels zooxanthellae and only zooxanthellae it should logically be better looking not white.

are the pigments expelled too?
or is the pigment creation linked with process that get distrupted during bleaching?

 

Coral Reef Bleaching

according to this a a couple of others I have just quickly checked out
it seems that whilst the Zoos are not primarily responsible for colour, they do have an active role in the processing of pigment cells
thus with reduced Zoos, = reduced colour, and ultimately white

Steve

 

this is very interesting