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Discussion Starter · #1 ·
How do bleached corals regain their zoox? Is it through finding a more adaptive zoox (say to high temps or light intensity) from neighboring colonies or is it by repopulating the coral's remaining zoox? What is the chemoreception theory in regards to zoox repopulation....is the coral tissue seeking out zoox and the zoox seeking out the coral?

Maybe I've had too many chocolate bunnies and none of this matters, or has this been debated to death and I'm late to the party?

Thanks!

~Nikki~
 

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Nikki, it appears that corals can draw zoo's from the water column, remember they are basically specialized dinoflaggelates, which like cyanobacteria abound.
As to the actual mechanism that cause expulsion and re adoption, I will let one of the learned get into detail.
This is worth a thread of its own :D
 

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Master of Perplexity
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Well, here's an idea born of too much thinking and maybe not enough research or reading! As I understand, since the corals expulse the zooxs due to oxygen poisoning (right?), couldn't they just take them back in later, when the oxygen levels decrease, with the latter process a lot slower than the former?
 

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So do the zoox reproduce as needed to meet the corals needs or is there documented evidence that they can expell and then adopt zoox that are better able to deal with changes in environment?
 

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so the bits of my capnella that went green/white might regain some zookies eventually? thats good, cause two branches of it must have horked them up somewhere cause the third looks beautiful and the other two dropped off and are 'deflated' looking
 

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Discussion Starter · #7 ·
Well, here's an idea born of too much thinking and maybe not enough research or reading!
How so?


If it isn't a total bailout, then I would think the remaining zoox may repopulate....could it be a combination of both? Some remnant zoox repopulating and adjacent zoox coming in?

~Nikki
 

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Rotten Kitty
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In reading about PAR today I found several articles on bleaching of reefs. It seems that most corals that recover only lose about 60% of there zoox (I think this should be the new spelling :)) Many corals have several different types and may expell only a certain color, how they know the difference is beyond me, maybe the different colors live in different regions of the coral, But I've seen some in my tank lose most of there brown and turn green.
 

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Jimbo the vast majority of zoox are brown. they contain two main pigment, perriden (yellow) and cholorphyll (green) together they make a lovely brown. Mostly what you are seeing by your corals turning a different color is the dominance of particular types of pigment protiens, based on the color of light you subject the colora to.

On the Bleaching, I believe the large majority of zoox bail out is caused by the release of a heat stress enzyne by the coral itself. As Jerel said in most cases not all of the zoox is released so thier is a chance of recovery, but the chances are still very low.

Well, here's an idea born of too much thinking and maybe not enough research or reading! As I understand, since the corals expulse the zooxs due to oxygen poisoning (right?), couldn't they just take them back in later, when the oxygen levels decrease, with the latter process a lot slower than the former?
And here I am thinking asking questions in this forum was a good means of research, ;) . Reagaining is a tough one, with the coral losing the vast majority of its food suppy, ts going to be hard for it to maintain the energy it needs to stay alive while recouping, not imposible but pretty tough situation. Can you explian the oxygen poisening thing a bit more???


Mike
 

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Hi Nikki, Good to see you!

Yardboy, ditto Mike's question, more info on the O2 poisoning, please?

I have no evidence, but suspect corals swap and injest each others zoox without any bleaching episodes or cataclysmic events?
Just anecdotal, but I got a (particular shade of) purple staghorn, and could swear other corals "liked" it's zoox and over successive weeks took them in and started showing that same color more strongly.
 

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Discussion Starter · #11 · (Edited)
Hi TG! Good to see you, too!

TG, that is an interesting observation and I have a friend that experienced something similar with a coral. Could it be that corals are always on the lookout for a better zoox? One that may be better suited for their environment, where the coral gets a bigger payoff with "food" from the new zoox and vice versa? How do they know the zooxanthellae are in close proximity to ingest them? Does it work by chemoreception?

~Nikki~
 

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Rotten Kitty
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Jimbo the vast majority of zoox are brown. they contain two main pigment, perriden (yellow) and cholorphyll (green) together they make a lovely brown. Mostly what you are seeing by your corals turning a different color is the dominance of particular types of pigment protiens, based on the color of light you subject the colora to.
In my particular case the coral had green polyps and was brown otherwise. It became ghostly white except for the polyps which stayed green, evently the green spread to the rest of the coral. I'm pretty sure it was oxygen poisoning the caused the stress, it could be just a quincedance that the perriden went south or that conditions within the coral itself led to the demise of the zoox but was ok in the polyps, the polyps are extended from the main body some possibly allowing more gas exchange. Many corals have polyps that are a different color.
 

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Master of Perplexity
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As far as oxygen poisoning, works the same way it does for us. Don't dive too deep, or you can definitely get too much oxygen from increased gas pressure. Corals have a set amount of zoox at a given instant, producing the corals needs in oxygen. Excess light to the zoox increases production of oxygen to the coral, resulting in "poisoning" from oxygen radicals and peroxides formed from the oxygen.
 

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Nik, what's chemoreception? It's got to be (at least partially) dependant on the photoperiod and intensity, wouldn't you think?

Jerel, yeah, that's a Good hint!! Do the different zoox inhabit different areas or just mix it all up everywhere?

Yardboy, excellent explanation! Thanks!! So, when the coral starts getting oxygen poisoning, it starts expelling zoox?

Jimbo, that seems odd, that the polyps kept their color (and presumably their zoox), while the body went white. I've never heard that before!
 

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Excess light to the zoox increases production of oxygen to the coral, resulting in "poisoning" from oxygen radicals and peroxides formed from the oxygen.
Corals produce enzynes such as Superoxide dismutase, Catalase and Ascorbate Peroxidase, all three of these are specifically designed to combat hyper-oxygenated conditions with in the coral itsself. What scews things up is eposing the coral to higher temperatures. At temperatures over 30c the heat distrupts the above enzynes and stops thier ability to respond as they normally do. Low- or high-temperature shocks results in zooxanthellae low as a result of cell adhesion dysfunction. This involves the detachment of cnidarian endodermal cells with their zooxanthellae and the eventual expulsion of both cell types.
It has been hypothesized that bleaching could also be something that the coral wants to do, in order to add more productive/protective stains of zoox.
Thier are actually alot of reasons that corals can bleach, here are a few I know about.
Solar Irradiance
Sedimentation : sediment loading could make zooxanthellate species more likely to bleach
Fresh Water Dilution:
Inorganic Nutrients: this one relates to hobbests pretty good.
Protozoan infections:

Mike
 

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Discussion Starter · #18 ·
Jerel....I was thinking that maybe a coral can host more than one type of zoox at a time? ;) Thanks. I'll ask the same questions as tankgirl. Maybe one type of zoox is better suited for the bottom of the coral? Although mixing together would make sense.

TG - chemoreception is a sense (like our sense of smell or taste). Basically, a chemical is secreted to say "Hey, I'm over here!" It can be used in many ways, like mate attraction or defense. I just wondered if the zoox sends out a signal that is saying to the coral..."Here I am, if you need some zooxanthellae!" and then the coral picks it up, or maybe the coral secretes a chemical? Or maybe it doesn't work like this at all. I was trying to figure out how the coral knows the zoox is there.
 

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Corals are mostly just capturing prey and eating. If they happen to eat a better zoox, it can out compete the ones that are dominating the coral at that time.

There's no chemical signals traveling around. For the most part, these dinos are traveling around looking for habitat. If they happen to be ingested, the habitat is right for what they need, you have a marriage made in heaven.

Corals have to be able to do this simply because the "habitat" that the coral creates is changing as the coral grows, the seasons change, stuff happens.
 

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Rotten Kitty
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I was reading this article on calcification
http://www.advancedaquarist.com/issues/apr2002/chem.htm


So it does not appear that zoox have much todo with calcification, except for providing food for the cells to move ca and carbonate. If anything lighting above natural levels that the coral is use to could affect co2 levels in the coral adversly affecting calcification. Now I wonder if one type of bleaching could be the affect of two much light and the coral reacting to this situation. Although we call this oxygen poisoning the coral could just be adjusting for for lowered co2 levels.

This article also explains about phosphate, now many have said that high phosphate levels have killed there corals, but from this reading it affects calcification levels. Nice to know why phosphate levels affect coral growth. It also interesting to note the magnesium can affect calcification levels.

I'm going back and rereading this article over since I only assimulated about 20% the first time through. :)
 
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