I am on a quest to understand more about bleached corals. There is a thread in the SPS Forum regarding a certain coral that a number of us bought and received bleached. The coral is clearly alive for me three months later but still as bleached as the day it came. I keep hoping the base color is getting a hint of green to it but I really think it is still as white as it was 3 months ago. The polyps are out all the time and I think it is growing ever so slightly down the sides. It is an encrusting monti that should be green with red polyps. It is white with neon pink polyps for me and others. So when a coral bleaches what is going on? The release of zooxanthellae, right??? but why has it not died or repopulated the zooxanthellae?? Is there soemthing else going on with this coral. So when corals bleach and continue to live what is really happening for that coral??
Bleached coral question
- Thread starter slojmn
- Start date
greenbean36191
Premium Member
There are lots of possibilities why the coral doesn't repopulate with zoox.
1.) Conditions that induced the bleaching haven't been corrected. Too much or too little light, too little flow, high or low temps, disease, waterborne toxins, etc. are all possibilities.
2.) There aren't appropriate zooxanthellae to be taken up from the water and there either aren't any viable zooxanthellae remaining (unlikely) or conditions aren't favorable for them to reproduce. Since the N from the corals acts as fertilizer for the zoox, if the coral isn't eating much and the water is low in N, the zoox could be limited.
3.) There just hasn't been enough time.
4.) ???
When corals bleach and keep on living essentially all that's happened is that the coral has lost its main source of carbs (energy). There are other consequences such as decreased calcification, but they're not usually life-threatening. As long as the coral gets enough food through other means, theoretically the coral could live without the zooxanthellae indefinitely. Most of these animals aren't evolved to do that though since the water near reefs is poor of other energy sources. Eventually in the wild either the coral dies or it repopulates with zoox by taking them up from the water and by division of the remaining cells.
1.) Conditions that induced the bleaching haven't been corrected. Too much or too little light, too little flow, high or low temps, disease, waterborne toxins, etc. are all possibilities.
2.) There aren't appropriate zooxanthellae to be taken up from the water and there either aren't any viable zooxanthellae remaining (unlikely) or conditions aren't favorable for them to reproduce. Since the N from the corals acts as fertilizer for the zoox, if the coral isn't eating much and the water is low in N, the zoox could be limited.
3.) There just hasn't been enough time.
4.) ???
When corals bleach and keep on living essentially all that's happened is that the coral has lost its main source of carbs (energy). There are other consequences such as decreased calcification, but they're not usually life-threatening. As long as the coral gets enough food through other means, theoretically the coral could live without the zooxanthellae indefinitely. Most of these animals aren't evolved to do that though since the water near reefs is poor of other energy sources. Eventually in the wild either the coral dies or it repopulates with zoox by taking them up from the water and by division of the remaining cells.
Greenbean3691, thanks so much 
. Very helpful and just what I thought. Is the N- nutrients in your points??? or nitrates?? Not sure what the conditions were that the coral bleached anyways since it came to me completely bleached. I have kept it in a shaded section of the tank. I run a somewhat nutrient poor system but it isn't all that nutrient poor because I do have some algaes around that are surviving off the nutrients. The tank in general is humming along very well right now and corals are looking awesome with deep, rich colors so I am hoping the environment is good. I guess I have to wait and see what happens for htis little guy. In the meantime I am getting another frag of it from a different source.
. Very helpful and just what I thought. Is the N- nutrients in your points??? or nitrates?? Not sure what the conditions were that the coral bleached anyways since it came to me completely bleached. I have kept it in a shaded section of the tank. I run a somewhat nutrient poor system but it isn't all that nutrient poor because I do have some algaes around that are surviving off the nutrients. The tank in general is humming along very well right now and corals are looking awesome with deep, rich colors so I am hoping the environment is good. I guess I have to wait and see what happens for htis little guy. In the meantime I am getting another frag of it from a different source.
greenbean36191
Premium Member
N= nitrogen
MCsaxmaster
New member
And just as a side note: even under the worst bleaching events in nature where the corals look stark white they still retain ~10% of the original density of zoox. Bleaching results in a major reduction of the algal population, but not the complete elimination of it. Even if there are no zoox. to be had from the environment (which is unlikely) the coral should still be able to regrow a symbiont population from the existing population, providing good conditions exist.
MinibowMatt
Active member
one thing I noticed after recovering from two minor->medium sized bleaching events, is that when conditions arent ideal and stable for at least 2 weeks, zoox will not repopulate. Once I had stable parameters things came back rather quickly.
I have had my share of "learning experiences". 1 was from a drop in alk while I was on vacation. I bleached nearly all zoas, fleshy LPS. didnt terribly effect my leathers or caps. Acros lost color, but quickly regained. the first things (nuclear green palys) started coming back after 3 weeks. The l absolute ast thing coral to regain total coloration was a frogspawn, and that took 4 months.
The first 2 bleaching events were from lighting changes. I bought new bulbs and did not raise the pendant high enough the first time. burned zoas badly, that coupled with poor parameters caused a lot of losses and took 8+ months for recovery. this was luckily only a 10g prop.
The second was from a crazy shift in spectrum on brand new bulbs. I burned in new XM 20K carefully over 3 weeks with a combination of lowering my pendant and using window screen. All was well after 3 weeks. Shortly thereafter they started progressively burning whiter and whiter... I didnt catch it in time due to life, and i bleached several higher up LPS and zoas that time. That recovery period was also shortened by stability and took about 5 months...
However.. I learned tons from my mistakes, and through it ll I didnt lose much but time.
I have had my share of "learning experiences". 1 was from a drop in alk while I was on vacation. I bleached nearly all zoas, fleshy LPS. didnt terribly effect my leathers or caps. Acros lost color, but quickly regained. the first things (nuclear green palys) started coming back after 3 weeks. The l absolute ast thing coral to regain total coloration was a frogspawn, and that took 4 months.
The first 2 bleaching events were from lighting changes. I bought new bulbs and did not raise the pendant high enough the first time. burned zoas badly, that coupled with poor parameters caused a lot of losses and took 8+ months for recovery. this was luckily only a 10g prop.
The second was from a crazy shift in spectrum on brand new bulbs. I burned in new XM 20K carefully over 3 weeks with a combination of lowering my pendant and using window screen. All was well after 3 weeks. Shortly thereafter they started progressively burning whiter and whiter... I didnt catch it in time due to life, and i bleached several higher up LPS and zoas that time. That recovery period was also shortened by stability and took about 5 months...
However.. I learned tons from my mistakes, and through it ll I didnt lose much but time.
