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Changing Acropora Colours

By Eric Borneman, Andy Hipkiss and Minh Nguyen. Posted to reef-l emailing list, Saturday the 11th to Wednesday the 29th of November 2000.

Andy Hipkiss

I've got a situation in my tank that is vaguely interesting ... at least to me :-)

Of late I've been running my tank pH a little lower that previously (i.e 8.0 to 8.15 rather than 8.2 to 8.35). I've noticed that my red A. millepore has become more highly couloured than before whereas a couple of A. nana frags have lost a significant portion of their purple colouration. Now is this coincidence or has anybody else noticed that red acro's seem to prefer a lower pH whereas purple acro's require a pH a couple of points higher.

I have a sky blue A. yongei that doesn't seem to care either way .....

Curious! Any thoughts?

Eric Borneman

I would highly suspect there are other factors besides the pH that are altering the coral pigmentation. Also, changes (or brightening of colors) may not neccesarily indicate a "preference" or even a happy condition. A lot of people think coral reefs are really pretty after they bleach!

Minh Nguyen

This is certainly true. When my coral bleach earlier this year after my RIO pump failed and poisoned the water, the corals look very beautiful in a un-healthy way. All the corals were pastel blue, pink, red etc. Fortunately, most of my corals recovered.

Andy Hipkiss

I would highly suspect there are other factors besides the pH that are altering the coral pigmentation.

Quite possibly. I guess I was hoping that others had had a similar experience and could point me in the direction of those other factors if it wasn't pH. Although pH is "just a number" it does imply quite significant water parameter shifts so I was theorising ... erm wildly guessing -) ... that it's a candidate.

Other possibilities could be the MH's aging, increases/decreases in NO3 or PO4 levels due to variations in the mass of foodstuffs I'm feeding the tank, or indeed what's in the food ... I have made up a new mix a few weeks ago. I have recently mounted a new frag so I guess I should throw Devcon into the possible mix. Ca / alk hasn't changed.

Also, changes (or brightening of colors) may not neccesarily indicate a "preference" or even a happy condition.

I wouldn't deny that for one moment. However I would take growth and particularly polyp extension as a reasonable indicator (or am I on shaky ground here?).

A lot of people think coral reefs are really pretty after they bleach!

To a greater extent this is very true, but I'm not talking about pastel colours. Certainly the A. nana is bleaching to a degree as the colonies are not turning brown, rather a paler colour than before. However the A. millepore is doing the reverse. This might actually be a cyclical thing (certainly it has occurred 2 or 3 times before ... but this tends to rule out the MH bulbs aging) ... however I never really questioned it before.

The relevance now is that I am setting up a small grow out tank(s) to be attached to the main tank. If it turns out that the colouration of these two colonies (well multiple colonies but based on two original wild colonies) then the concept runs along the lines of the "nana" tank is the one where I'll introduce the kalk whereas the "millepore" will have the outlet of the CaCO3/CO2 reactor. If this turns out to be significant then I will change the arrangement of the various inlets/outlets. The original plan was to pump from the sump to just a single frag tank. However, an alternative would be to have two tanks that both draw from the sump rather than being in series and hence maintain a pH differential to an extent.

Oh pH is taken via a freshly calibrated meter using Hanna buffers and an accurate thermometers FWIW. And the Latin names of the colonies is open to debate -) .... pictures of which are on my web site just to show I know the difference between solid and pastel colours ;-)

Eric Borneman

Other possibilities could be the MH's aging, increases/decreases in NO3 or PO4 levels due to variations in the mass of foodstuffs I'm feeding the tank, or indeed what's in the food .. I have made up a new mix a few weeks ago. I have recently mounted a new frag so I guess I should throw Devcon into the possible mix. Ca / alk hasn't changed.

I think those are certainly possibilities! Also, simple physical and chemical changes in the biota as the tank ages. We tend to forget that the same conditions that cause things like algae blooms, successions, etc. are at work. It's not just us adding and subtracting, but the very biological and ecological processes occurring.

I wouldn't deny that for one moment. However I would take growth and particularly polyp extension as a reasonable indicator (or am I on shaky ground here?).

Or a hungry coral! So many corals exposed to strong light in the wild often remain closed, preferring to feed at night. Are they open because they need the energy from feeding or because they are sensing food in the water during the day rather than at night? Good question to ask, I think.

Just some things to ponder, and you might just as equally be right in your assessment - just trying to foster thought.

Sorry for the long delay in answering again.

Andy Hipkiss

Interesting that you should reply a fortnight later, it's allowed me to more closely watch the progression and note the changes.

I think those are certainly possibilities! Also, simple physical and chemical changes in the biota as the tank ages. We tend to forget that the same conditions that cause things like algae blooms, successions, etc. are at work. It's not just us adding and subtracting, but the very biological and ecological processes occurring.

I suspect that your are correct here, indeed were correct before when you mentioned bleaching.

What has happened is indeed a mini-bleaching event, with various species forming a cascading chain, one being more "sensitive" than the other, one suspects. Equally, the recovery has followed the same progression. Strangely, growth rates do not appear to have been affected though. However since we are only talking a few millimetres a week than I doubt I would notice even a 50% reduction in rate of change. I am left pondering what would cause such an event, especially one so short lived (4 weeks). If it were overnight temperatures (which would fit in with the turn in the weather) then the same "should" still be true, but its not.

Therefore, I tend to agree with your "chemical changes" assertion, mainly due to an occurrence of a small area of brown algae (perhaps dino's). Initially I did a 10% water change, which seemed to be the trigger for the acro's to darken, however the algae remained. Thus, I built myself a carbon reactor which is run 2 hr/day and drains dry the other 22 hours. This seems to be having the desired effect.

Or a hungry coral! So many corals exposed to strong light in the wild often remain closed, preferring to feed at night. Are they open because they need the energy from feeding or because they are sensing food in the water during the day rather than at night? Good question to ask, I think.

Light bulb moment wrt your first phrase. It kinda surprised me some while ago when I added an additional skimmer to my system (they are called Deltec's over here ... DAS EX's I believe in the US). And this prompted an almost an immediate polyp extension (we are talking a few hours here). If we take Tunze's claims at face value (re not removing planktonic elements) then the effect of the additional Deltec would, at least, not disagree with your statement.

Anyway thanks for your reply ... just wished I'd paid closer attention to you earlier, although maybe I needed to respond to the events rather than pre-empt them.

Created by liquid
Reefs.org
Last modified 2006-11-24 18:39
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