Some Reasons Why Corals Turn Brown

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Some Reasons Why Corals Turn Brown

Postby danggit » Mon Aug 22, 2016 6:13 pm

Hi everyone,

I was researching this topic as its happening to some of my blastos and other corals. I found this great response (at least, I was more convinced of this than others I found) to a post of similar topic at Reefcentral.com, credits to the poster also mentioned below. I left out the replies from the other posts so its just a condensed response from this user.

From 'tmz' at http://www.reefcentral.com/forums/showt ... ?t=2092870:

"
Nutrients and/or light can cause browning and/or bleaching ,imo.

Zooxanthelae are brown. They produce oxygen and the sugars the coral needs and use C02 water and light to do so. They also produce oxygen.

When zooxanthelae are highly active as in high light they put out more oxygen than the coral can handle ;so, some are expelled as the coral tries to regulate harmful oxygen radicals. Color is affected by light as the coral sheds brown zooxathelae when more light is avaialbe and develops protective pigments which affect color too. The overactive , overplentiful zooxanthelae can lead to bleaching as the coral may expell too many or become photinhibited or are harmed by the oxygen radicals.

Excess nutrients, organics, nitrates can produce browning as they fuel more brown zoxanthelae. Bleaching can also occur as oxygen radicals increase .Some of the excess zooxanthelae may compete for carbonate with the coral.

Low light can make the coral produce more zooxanthelae and brown it. But ifi t's too low it can also lead to bleaching.

Stress from infection , a predator or parasite, a wound or sting ,trouble in calcification brought on by high PO4 may also lead to browning and/or bleaching.

Zooxantelae can use nutrients including organics and inorganic nitrogen like nitrate . When in excess more zooxanthelae grow than are needed leading to similar issues with browning.


An algae scrubber won't remove free copper, Cu which is the toxic type . It can be lethal in small amounts in parts per billion. Algae like any other organism will take up some amounts of bound copper. Personally, I wouldn't count on algae to prevent metal toxicity which might otherwise occur. Doesn't sound like metal toxicity is your problem in any case.

32 C/89.6 F is hot and likely will likely do damage. High temps accelerate metabolism . Zooxanthelae growth accelerates along with other biological processes in the tank to a point where the zooxanthelae becomes pathogenic to the coral rather than symbiotic leadingto browning and or bleaching. "

Some of you may already know this by heart but I thought to highlight this to those that don't, or needing a refresher (including me).

Hope this helps.

Danggit
danggit
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