Let me start by saying that the "factors" I gave are pretty much gathered from things I have read, been told, and general scientific "common-sense".
If an organism is sessile and requires its environment to bring it food and get rid of waste, maximizing the surface area will facilitate this (expand the polyps). But this also requires energy, so if it's not needed, it doesn't make sense for the organism to do it. That can either be because it doesn't need to or because it can't really invest the energy into doing so.
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Originally Posted by skeety
okay...so with an open top, open sump, the return pump dedicated to surface aggitation, and a MR2 skimmer adding TONS of air...I'm hoping to exclude respiratory needs. As I'm pretty sure the water is mixing with the air enough.
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I think the respiratory need would come more into play with oxygen deficiency. Although it might also play a factor if the coral is getting too much O2 (overphotosynthesizing) - and that would contradict the "no PE with too much light" response. As you can see, there are many interrelated factors here.
Keep in mind that most Acropora exhibit little or no
polyp extension in the wild during the photosynthetic period. I have no idea why, but it's obviously not a clear sign of the colony's state of well being. It might well be aggression in the wild and perhaps it's as simple as them not being able to "unlearn" that behavior in captivity. But I've seen frags off the same colony expand in one tank and not in another. Agression was not a factor, so that means it's not the only factor.
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As for energy needs...am I to believe if the corals starving, I'd see greater PE regardless of other conditions? On the opposite end...if I'm getting good growth..can I assume that the SPS's energy needs are being met?
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Hard to say because the factors are interrelated. A "starving" coral may not have the energy to devote to PE. But they also can't feed very well with polyps in. Perhaps "starving" is a poor term.
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Should I maybe decrease my MH light cycle?
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I wouldn't. I think your lighting is fine. How are you acclimating them? Also, how old are these corals and how old is your tank?
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This confuses me...cause some of the reasons you gave for PE would lead me to believe the coral is unhappy. i.e. Energy needs and respiration. If it's not getting enough energy, you'd see PE, but the coral would be unhappy. Same with respiration, right?
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Well, as you can see, it's not as easy as it would be if there was a single variable. There are lots of SPS keepers who lament about the lack of polyp extension. I have a couple Acros in my tank that just never expand during the day regardless of conditions. I think that as long as there is extension at some point in a 24-hour cycle, the coral is doing well. After all, they poop out of the same hole they eat through.
If they aren't expanding, their metabolism may well be shut(ting) down. The only time I worry is when I see no PE day
or night.
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We all seem to strive for really good PE...but that seems contradictory to the corals health given that info.
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In what way? If the coral is growing well, expanding the polyps places little demand on the colony. That this might increase the amount of prey that is captured or increase photosynthetic products is a good thing. More raw materials to be had. Lack of extension may also be a temporary thing until the coral acclimates to its conditions. In all, we need to learn that it's not good or bad, but rather makes the coral look "better" to us. Does that matter? You're the judge.
But to rephrase my earlier statement. If polyps are expanded, it's probably not a sign of stress. I've yet to loose a coral that exhibited daytime PE. However, if the polyps are not expanded it may or may not be a sign of stress.
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I really do appreciate your input...so I hope you don't mistake me for being argumentative....I'm just trying to understand.
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Not at all.
I come across as being argumentative all the time. I like to think of it as "stimulating the conversation."
