Acropora Fragility

[Trey]

I am hoping for some educated answers here... although it may be an unanswerable question.

Why do acropora in general seem to be more sensitive than other coral?

I understand that they are fast growing and easily propagated reef builders given ideal and consistent environmental conditions... but what benefit (evolutionarily) comes from being more susceptible than other corals to comparatively small parameter changes?

 

[bobby.w.hodges]

I am certainly no expert, but I believe it's due to the very thin layer of flesh they have on top of the skeleton. I believe that the thin flesh is easily damaged via stress and or water parameters and then it's all down hill from there unless the stressor is resolved.

 

[Mono]

Well, it obviously it helps them "trick" some dumb humans into devoting their entire lives to caring and providing for them often to the detriment of their own human off-spring. That's a pretty huge evolutionary advantage in my book.

 

[92Miata]

I am hoping for some educated answers here... although it may be an unanswerable question.

Why do acropora in general seem to be more sensitive than other coral?

I understand that they are fast growing and easily propagated reef builders given ideal and consistent environmental conditions... but what benefit (evolutionarily) comes from being more susceptible than other corals to comparatively small parameter changes?

Evolution doesn't work like that. Populations evolve traits as a result of environmental pressure- not to get 'benefit'. Things that live reproduce, things that die don't. Population as a whole becomes more like the individuals who survive.

Being able to survive a wide range of - say calcium - levels isn't a benefit if the environment around you has stable calcium levels - and can be a detriment if the metabolic cost of having that ability is high.

As to Acropora specifically - they're not that sensitive - we just generally do a terrible job reproducing their environment. The areas they come from have dissolved nutrient levels that are very low - but also an infinite supply - with enormous amounts of food/plankton in the water. They are washed constantly with clean water, which whisks away their waste.

Its honestly a testament to how hardy Acropora are that they survive at all in aquaria - with basically no solid foods (they're almost completely photosynthetic in tanks) when they accrue so much from food in the wild.

 

[galactic_coral]

There have been some studies done that have found that several types of bacteria(both good and bad) live in symbiosis with corals. During a study of why reefs are bleaching they have come to the hypothesis that these bacteria are taking hold when the coral is stressed from environmental changes. When the coral becomes stressed the cyano, vibrio, or whatever else may be living within the coral or its skeletal base grows rampant and outcompetes the coral for its own body causing RTN.

They have done experiments where they have put some Acros through full antibiotic treatments cleaning them of all bacteria and the coral was able to live through big temp swings with no adverse effects. The only problem is when they do these treatments is that it's also hard on the coral and they struggle to get them all the way finished with the antibiotic cycle without the same outcome that they want to prevent.

In the end we know that nature is a cruel but beautiful thing. I just do my best to mimic it with my systems. All of my parameters are run at natural sea water. No elevated kh or other elements. I find that when we use high kh (9 or above) as a growth stimulant that the acro skeletal structure grows faster but becomes very weak where any touch would break a branch if we aren't careful. This is compared to keeping kh at 7.5-8.5 where I have trouble clipping with bone cutters.

Anyway, we still don't know everything that's going on and these types of discussions are always productive.

 

[Trey]

There have been some studies done that have found that several types of bacteria(both good and bad) live in symbiosis with corals. During a study of why reefs are bleaching they have come to the hypothesis that these bacteria are taking hold when the coral is stressed from environmental changes. When the coral becomes stressed the cyano, vibrio, or whatever else may be living within the coral or its skeletal base grows rampant and outcompetes the coral for its own body causing RTN.

They have done experiments where they have put some Acros through full antibiotic treatments cleaning them of all bacteria and the coral was able to live through big temp swings with no adverse effects. The only problem is when they do these treatments is that it's also hard on the coral and they struggle to get them all the way finished with the antibiotic cycle without the same outcome that they want to prevent.

In the end we know that nature is a cruel but beautiful thing. I just do my best to mimic it with my systems. All of my parameters are run at natural sea water. No elevated kh or other elements. I find that when we use high kh (9 or above) as a growth stimulant that the acro skeletal structure grows faster but becomes very weak where any touch would break a branch if we aren't careful. This is compared to keeping kh at 7.5-8.5 where I have trouble clipping with bone cutters.

Anyway, we still don't know everything that's going on and these types of discussions are always productive.

That’s super interesting. Do you have any links to the papers?

 

[Pdash]

I am hoping for some educated answers here... although it may be an unanswerable question.

Why do acropora in general seem to be more sensitive than other coral?

I understand that they are fast growing and easily propagated reef builders given ideal and consistent environmental conditions... but what benefit (evolutionarily) comes from being more susceptible than other corals to comparatively small parameter changes?

Home aquariums are evolutionarily novel environments, corals that are susceptible to shifts in water parameters obviously don't have to deal with those shifts often in the wild or they would be adapted to them. Acropora are incredibly resilient to all sorts of stressors but there are limits. It is also important to understand that just about every possible phenotype has an evolutionary trade off associated with it, just because some trait seems "good" to us does not mean it increases reproductive success in an organism's natural habitat.

 

[burningmime]

Some interesting answers here, but I don't think any have addressed this part of OP's question: "Why do acropora in general seem to be more sensitive than other coral?"

 

[Pdash]

Some interesting answers here, but I don't think any have addressed this part of OP's question: "Why do acropora in general seem to be more sensitive than other coral?"

Other corals are adapted to different environments. All corals do not fill the same niche. I'd also guess that quirks of different animals evolutionary history make them more or less difficult to keep in an aquarium. It seems that all reef building corals are more sensitive than non-reef building corals, it seems apparent to me this has to do with the process of laying down their skeleton making them more prone to die off as a result of parameter fluctuations in a home aquarium. Of course this is mostly irrelevant in the wild, there are no rapid alkalinity swings in the ocean so they aren't adapted for it, the soft corals may not be adapted for it either, but they also don't rely on calcification in the same way as Acropora, and as a consequence carbonates in the water don't effect them in the same way that stony corals are effected.

Of course Acropora tend to be more sensitive than other stony corals in our tanks, but again they don't fill the same niche on the reefs, and the same types of issues, as described about, would apply between different stony corals as between stony and soft.

This is kind of like asking why keeping a hawk as a pet is more challenging that keeping a sparrow even though they are from the same environment.

 

[92Miata]

Some interesting answers here, but I don't think any have addressed this part of OP's question: "Why do acropora in general seem to be more sensitive than other coral?"

Because we (generally) do a poorer job of reproducing the environment they evolved in than for other corals.


For instance - phosphate - the levels in the ocean are low. A couple parts per billion. But with a nearly an infinite supply of water washing over a coral - they have essentially an infinite supply when they need it.

This is impossible in a contained body of water - keeping a low concentration and high supply. So instead we walk the tight-rope of low-but-not-too-low.


A lot of corals we keep (aside from acropora) come from semi turbid waters - lagoons and such - they deal with silt, they deal with temperature swings associated with tides, salinity swings. Some anchor themselves in silt.

 

[Pdash]

This is impossible in a contained body of water - keeping a low concentration and high supply. So instead we walk the tight-rope of low-but-not-too-low

Of course it's possible, we add phos and remove it from our tanks all the time, and people maintain po4 at different levels consistently all the time, there being an "infinite supply" as some sort of distinction between the ocean and our tanks doesn't make any sense. Now, since the water volume is so high in the ocean the po4 can't all be stripped out as a result of coral growth and po4 remains relatively low and stable (stable/low po4 is absolutely not an accurate description of some reef environments by the way), but the same is possible in principle and practice in our home aquariums that is to say low and stable po4.

 

[92Miata]

Of course it's possible, we add phos and remove it from our tanks all the time, and people maintain po4 at different levels consistently all the time, there being an "infinite supply" as some sort of distinction between the ocean and our tanks doesn't make any sense. Now, since the water volume is so high in the ocean the po4 can't all be stripped out as a result of coral growth and po4 remains relatively low and stable (stable/low po4 is absolutely not an accurate description of some reef environments by the way), but the same is possible in principle and practice in our home aquariums that is to say low and stable po4.

The OP isn't asking how corals can survive in a reef tank - he's asking for the critical differences between the ocean and reef tanks that make acropora hard.

The combination of the inexhaustibility of food and low levels of pollutants because of the sheer volume of the ocean is ABSOLUTELY one of these things.

There are things we can do to mimic this - nobody is denying that - namely high input, high output - but many people get it wrong - which is why we see threads all over the place with "My phosphates were .4 and I used RowaPhos and now everything is dead".

But this is inherently a tightrope - which is why acropora *seem hard*

(stable/low po4 is absolutely not an accurate description of some reef environments by the way

I most certainly did not say it was a description of all reef environments - just high energy reef crest environments where acropora are *typically* found

 

[burningmime]

Because we (generally) do a poorer job of reproducing the environment they evolved in than for other corals.


For instance - phosphate - the levels in the ocean are low. A couple parts per billion. But with a nearly an infinite supply of water washing over a coral - they have essentially an infinite supply when they need it.

This is impossible in a contained body of water - keeping a low concentration and high supply. So instead we walk the tight-rope of low-but-not-too-low.


A lot of corals we keep (aside from acropora) come from semi turbid waters - lagoons and such - they deal with silt, they deal with temperature swings associated with tides, salinity swings. Some anchor themselves in silt.

Generally the way I've heard it is that oceans has very low dissolved inorganic phosphate which is what we're trying to avoid building up in reef tanks. But ocean has a lot of prey for corals (eg plankton), which contain phosphates in an organic form, while our tanks don't. It's a different kind of phosphate (and nitrate).