Alternative techniques 1: Exposure of corals in a reef tank

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Considering my budget, free time (both in shortsupply understatement), I am often amazed at the success I have with acropora corals in terms of growth and especially colouration.

I have spent considerable time pondering the reasons for my success:

Lots of advice, patience and late nights in the company of Liaquat, aka obi wan.........

All the SA reefers who have helped me learn from their experiences (and mistakes).......

With regards to the basics, I have them all in place, but nothing in the line of TUNZE, Powermoduls, bubblekings, chillers, profilux, Chillers, etc...........

I am not running zeovit, prodibio or dosing vodka, using, het even my light are just 150 watters in fittings without reflectors..........

How do I do it? The question most often asked when people see my tank for the first time....
The same question I have spent quite some time pondering and researching lately....

Thanks to Anthony for pointing out something which seemed insignificant, but the more i researched it, the more I came to understand how significant the practice of exposing corals to air could make a significant contribution to improved colouration in corals.

Now please, don't get me wrong, I am not punting a new cure all, magic pill, new method in reefkeeping. I am just analising seemingly insignificant practises, which could possibly have a synergistic effect on health of corals.........

Nor am I telling reefers to start lifting their corals out the water for a breath of fresh air, in fact, do not try the below, unless you fully understand the principles behind it................and even then.............proceed with caution...........

Enough blah blah blah, time to get to the point............

Lets look at the science:

Corals produce pigments to shade them from UV light, a well known fact......

In nutrient poor conditions, more light reaches corals, therefor more intense colour in lower nutrient levels, a well known fact......

Reef crest corals are often exposed to low air at low tides, especially during very low tides, a well know fact........

So waht happens when corals are exposed to air?
They poruce mucus, lots of it:

Submerged
Acropora released 1.7 l of mucus per m2 of reef area per day,
as opposed to:​

after air exposure, a regular event caused by extreme low tides




indicated that reef rim Acropora can release 4.8 l of mucus per m2 of reef area per day.

Coral mucus functions as an energy carrier and particle trap in the reef ecosystem


Christian Wild



1, Markus Huettel2, Anke Klueter3, Stephan G. Kremb4, Mohammed Y. M. Rasheed5 & Bo B. Jørgensen1


Furthermore:​

More than half (56–80%) of the released coral mucus immediately dissolves in the sea water, and this dissolved fraction provides afood source for planktonic bacteria....



This corresponds to 10–21 mmol of particulate organic carbon (POC), 1.5–1.8 mmol of nitrogen and 0.08– 0.18 mmol of phosphorus




.



Coral mucus functions as an energy carrier and particle trap in the reef ecosystem
Christian Wild





1, Markus Huettel2, Anke Klueter3, Stephan G. Kremb4, Mohammed Y. M. Rasheed5 & Bo B. Jørgensen1



Interesting................especially considering addition of carbon sources to tanks to feed bacteria, promoted as a nutrient way to reduce nutrients..............


My hunch is that even without adding sugars that the high density of fish and corals and inverts constantly releasing mucus in a closed water volume already has our carbon (as sugars) way far from normal, and this might be a case in point for skimming since so far it looks like skimmers are doing a good job of removing mucus as particulates.
Eric Borneman​






 
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So now what happens to those strings of mucus that we see coming off our corals (the undissolved part)


The less-soluble fraction .... of the exuded gel-like mucus
forms transparent filaments ......combine to mucus flocs.
Positive buoyancy, caused by enclosed gas bubbles and lipids, results
in a slow ascent of these flocs. Passing through the water column,
their sticky surface traps bacteria, algal cells and small carbonate
particles. Enriched mucus aggregates then accumulate at
the water surface and form opaque films that are concentrated by
currents and winds to produce whitish mucus threads. The accumulation
and subsequent fusion of these threads generate mucus floats..........

............Two hours after low tides with air exposure of the corals, the gel-like transparent mucus released from the corals has turned into a yellow, bubbly mass that smells strongly of dimethyl sulphide and contains on average 2,250 ^ 230mM POC, 220 ^ 40mM nitrogen and 2 ^ 0.1mM phosphorus
Coral mucus functions as an energy carrier and particle trap in the reef ecosystem
Christian Wild1, Markus Huettel2, Anke Klueter3, Stephan G. Kremb4, Mohammed Y. M. Rasheed5 & Bo B. Jørgensen1

A real detritus and particulate organic matter trap if you ask me...........

Obviously in a reeftank this happens on a much smaller scale, most of it getting skimmed out (according to Eric Bornemans priliminary look at skimmate, a major constituent of skimmate consists of coral mucus)

Already I see some benefits?
And what I find really interesting:

Roller table experiments16 using sea water or coral mucus each
mixed with a suspension containing zooxanthellae, fine carbonate
grains (,10 mm) or bacteria showed that, after 3–14 h of slow
rotation, aggregates had formed only in the cylinders containing
mucus. This shows that mucus functions as a trap for particles and
causes the formation of aggregates.
Coral mucus functions as an energy carrier and particle trap in the reef ecosystem
Christian Wild1, Markus Huettel2, Anke Klueter3, Stephan G. Kremb4, Mohammed Y. M. Rasheed5 & Bo B. Jørgensen1


And the mucus which is missed by the skimmer?

release of trapped air bubbles initiates a rapid sinking........to the sandy bottom of the reef lagoon.

Flux measurements with 4–6 stirred benthic chambers, placed
simultaneously on the permeable lagoon sands, show a rapid
decomposition of freshly produced coral mucus by sedimentary
bacteria20. Experimental addition of mucus to the chamber water
enhanced consumption of O2 immediately by 16–41% (Table 1).
Oxygen consumption owing to mucus degradation in the water
column accounted only for less than 10% of the total measured
consumption of O2, showing that the benthic community decomposed
more than 90% of the added mucus. The increased benthic
O2 uptake of 17–51 mmolm22 d21 suggests that at least 7% of the
carbon added as coral mucus was turned over per hour20.
Coral mucus functions as an energy carrier and particle trap in the reef ecosystem
Christian Wild1, Markus Huettel2, Anke Klueter3, Stephan G. Kremb4, Mohammed Y. M. Rasheed5 & Bo B. Jørgensen1


Bacteria food of note......
 
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Mekaeel

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exclllent ivan!!the facts that you have stated makes alot of sense.in documentarys on TV regarding SPS and low tide,i was amazed that at times acorpora can stay out of water for around 4 hours.in my personal system,at times i get a seio that sucks up a whole lot of air and chucks it into my system and then stops for a while.could this in any way contribute in helping the colours of SPS to practically glow?
 
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Well, hmmm, like i said,: I am looking at husbndry practises that may contribute toward coral colouration....

Coral exposure to air and reduced nutrients, therefor improved colour, possible correlation............?

Pumps blowing air into tank........?
Well maybe, the fineness of the bbbles could trap a bit of DOC,DOM, POM, etc. so small contribution maybe.
I have a carlson surge device recently installed on my system, produces a fair amount of bubbles, dont see the corals adversely reacting to it, waves crash over reef crests more often than we like to think......
Is a seio sucking in air in some small way simulating waves crashing........ you decide
 
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Now how does this apply to our systems????

The article I quoted from, is from a study of corals fringing a lagoon, something very few of us replicate in our systems. In fact something we should maybe look to replicate.

When I do my water changes, regular monthly, I expose most of my reef crest species to air for some time.....
Surely not as regular as the ocean, but enough to cause quite a hefty release of mucus from the exposed corals...............

Now in our tanks we do not have the planktonic larave which consume the dissolving part of the mucus, or does this help to populate our tanks with planctonic bacteria..........?
I do have a significant amount of planctonic life in my tank, but unfortunately it all seems benthic.
Something to be concerned about................ Unless you take a closer look at skimmate, of which the largest part is coral mucus. (thanks again Mr. Borneman for helping on that one)

I use a remote dsb in my sump, which is seperate to my skimer container, with a large and relatively lenghthy surface are, great place for any coral mucus aggregates to settle....

I believe it is important to note that the sandbed is not lit, as this would cause growth of macro algae, which would trap mucus aggregates and prevent them form settling onto the sandbed........... Once mucus starts degrading amongst macro algae, you are bound to have your macro algae covered by cyano in no time......
 
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And thanks Liaquat for helping on this one: What happens in nature during and after a low tide??
During: water temperature around the corals which are exposed in shallows increases slightly, which is done in my tank by leaving the lights on, as the sun does not quickly disappear when the tide is low. Sure your corraline will bleach, but this is natural anyway...........
After: A significant surge of water coming in to cover the corals . The incoming water is considerably colder (visible thermocline noticed by divers) and often laden with food from the deep that gets swept up.....
When i perform a water change, i do not heat the water, it is laden with new trace elements, minerals etc.......

The only thing lacking is the food element....
Will experiment with adding my sps food shortly after a water change, as i have noticed major polyp extension shortly after a water change.........
Always thought it was just because of the nice new water............ maybe, maybe not.
Something to look at for those that use unpolluted nsw, which has the live food content added for free.
 
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Very interesting information and I'm sure with further research you may be onto something.

I jsut have a thought - how do we know the corals we keep come from reef fringes and are naturally exposed to air at some time during the day?

Or put another way, do corals that are normally never exposed to air eg. at low tide (i.e. corals from deeper waters) react in the same way?

Or can corals adapted to deeper waters be "conditioned" to exhibit the same response over time. My feelign is yes, and that this is probably what is happening in your case.

Since your corals exposure to air is infrequent and not of the same scale as in nature, I think any of your corals that were collected form deeper waters, may either a) have become "conditioned" with time or b) because it is not as extreme as in nature that they can cope adequately i.e. this is a natural ability they have but it is not needed in their naturally deeper habitat but can kick in if necessary.

Clinton
 

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This is food for thought, no pun intended. Ivan how long are your corals exposed for during the water change?
 
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Very cool Ivan.

Thank you for these well sorted and researched thoughts which it seems are the first installment of the Zerovit philosophy.

One thing that I didn't understand was your first statement

In nutrient poor conditions, more light reaches corals, therefor more intense colour in lower nutrient levels, a well known fact......
.
Why in nutrient poor conditions does more light reach corals.

I always worked on the 'low nutrients = less zooxanthelae = more colour visible', also better food or UV protection etc. etc. = better colour.

Is it that with lower nutrient there is less life in the water column theirfore more light gets through?
 
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Low nutrients meaning not measureable (at least by hobbyist tes kits) levels of NO3 and PO4. Less of these nutrients available for zooxanthellae to feed off, therefor less zooxanthellae (brown colour in corals)... Also, a system with higher nutrients is bound to have more dissolved organics and particulate matter in the water column, reducing light reaching corals....

I jsut have a thought - how do we know the corals we keep come from reef fringes and are naturally exposed to air at some time during the day?
I suspectthe ones I keep are:
Having spent extensive time living / diving in the tropics, the most colourful corals are the ones highest up on the reef, i.e. reef crest acroporids/montiporas/porites, etc.
The higher up, the more olourful, even in lagoons the shallow water ones are exposed at low tides.

When corals are collected for the trade, more colourful = more money, so hardly believe collectors would dive deeper for browner acroporas, if the entire reef crest is flled with them.
Sure, there are nicely coloured deeper water acropora, but they are in a minority, so I
believe my assumption is not far off.....

Since your corals exposure to air is infrequent and not of the same scale as in nature, I think any of your corals that were collected form deeper waters, may either a) have become "conditioned" with time or b) because it is not as extreme as in nature that they can cope adequately i.e. this is a natural ability they have but it is not needed in their naturally deeper habitat but can kick in if necessary.
Absolutely, it is in their genetic make up I would assume, as acroporids from deeper water are generally destined to grow to a point where they protrude from the water.....

Would like to simulate the tidal variations to expose my corals more regularly, and for a few more days at a time, am looking into playing with some timers on my return pumps etc......

Ivan how long are your corals exposed for during the water change?
Lately anthing up to two hours for the upper reaches of the aquarium.
 
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I see you were talking reef tanks not natural environments in that instance, I thought you were talking about natural reefs, cool.

Two hours, and you don't switch off your lights? Amazing I know it happens in the wild, but my corals normally take some flack. Maybe I should try acclimatizing for longer and longer periods.
 
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Howsit going Ivan? Interesting thread you've started here. Always wondered about your corals being exposed to the air for so long during water changes and now we have the scientific research that backs it up. Will be following this thread closely.
 
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Aah my friend, good to see you here, was hoping you would chime in ..
Will be a bit difficult to say that my techniques are backed by sound scientific research, but its the possible (probable?) correlation which interests me.

Bacterial populations
Carbon source
Nutrient reduction
Colour enhancement

something to it?

Risky if you proceed without caution, but then again so is crossing the road.
 
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Like I said, I am not telling you to take your corals out for a suntan, Do not get into this without knowing the risks:

From
SOME ECOLOGICAL FACTORS AFFECTING CORAL REEF
ASSEMBLAGES OFF HURGHADA, RED SEA, EGYPT.



EGYPTIAN JOURNAL OF AQUATIC RESEARCH:

The present study found that bleaching
of coral colonies at the studied sites was due
to combination of light temperature and solar
radiation during the neap tide.
 
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Suppose like everything in this hobby its all about achieving the balance......

Guess I have been walking a very thin tightrope without knowing it...........

A tightrope worth walking, as long as you do the research............... and once again, proceed with caution.

W.r.t. bleaching, is it not an event of expelling zooxanthellae???????

Less zooxanthellae = brighter colours (if done gradually, giving coral time to produce photoprotective pigments)

the line between minimum zooxanthella/ max colour and bleaching...........

really fine line I guess...........

so far so good
 
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Suppose like everything in this hobby its all about achieving the balance......

Guess I have been walking a very thin tightrope without knowing it...........

A tightrope worth walking, as long as you do the research............... and once again, proceed with caution.

W.r.t. bleaching, is it not an event of expelling zooxanthellae???????

Less zooxanthellae = brighter colours (if done gradually, giving coral time to produce photoprotective pigments)

the line between minimum zooxanthella/ max colour and bleaching...........

really fine line I guess...........

so far so good
I agree Ivan. I realy do believe that the exposure to direct light does indeed stimulate extra photoprotective pigments (over and above what the exposure to intense lighting while sumerged will do).

Something to throw into the mix here....since corals are exposed to air during low tides, how does this affect their respiration rates for that particular period of time? Is the energy of coral then primarily focused on producing mucus and less on respiration? Maybe i'm reaching too far here but....let's say the energy of the coral is directed away from respiration (for that period of time) and focused more at mucous production, it would be correct to say that the metabolism will slow down (since the coral is not feeding and it would be conserving energy) and respiration will also slow down (as there will be no flow/alternating current) to assist the coral with respiration by supplying O2 and removing CO2. Now since the zooxanthellae also need to respire, would the coral not be burdened by the energy requirements of the unnecessary zooxanthellae and thus end up expelling unnecessary zooxanthellae?

Just considering things from an energy point of view..
 
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stimulate extra photoprotective pigments (over and above what the exposure to intense lighting while sumerged will do).
Eish, its five in the morning, and you really talking my language now......

I was just considering increased mucus production, (induced by a natural stressor), enhanced nutient export and contriution of carbon towards bacterial populations.....

You really got me thinking.....

let's say the energy of the coral is directed away from respiration (for that period of time) and focused more at mucous production, it would be correct to say that the metabolism will slow down (since the coral is not feeding and it would be conserving energy) and respiration will also slow down
Like the way you thinking........
Really like it a .lot. But then maybe you are reaching a bit far (although I think what you saying makes perfect sense....)

Just came across this in the lrterature:


ABSTRACT Extreme tissue retraction in the agariciid coral Coeloseris rnayen occurs during periods ofsub-aerial exposure. The retraction response appears to involve independent movement of oral and aboral tissue layers to such an extent that skeletal septa are uncovered. Tissue retraction results in asignificant paling in colony colour which does not involve any reduction in either zooxanthellae abundanceor chlorophyll concentration. Adaptive benefits of the response include ~ncreased albedo,leading to a reduction in absorbed solar energy of 10% for wavelengths between 280 and 700 nm, and possible avoidance of photochemical damage or photoinhibition at high solar irradiance. The degree ofretraction is governed by environmental conditions, including length of sub-aerial exposure, and intensityof solar irradiance
.

From:
Tissue retraction in the scleractinian coral​
Coeloseris mayeri, its effect upon coral pigmentation, and preliminary implications for heat balance B. E. Brown, M. D. A. Le Tissier, R. P. Dunne

So does not seem to loose too much zooxanthellae............... But we are talking about a coral which is already in a nutrient poor environment (natural reef), so probably does not have any excess zooxanthellae to get rid of in the first place.... so maybe your thinking not too far of...

From the above article, Some light at the end of the tunnel:

The extent, nature and significance of extreme tissue retraction in corals is worthy of further study for the phenomenon has the potential not only to affect apparent
pigmentation of corals, but also the incorporation of chemicals into coral skeletons

Now its really bed time.............




 

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