Thoughts on SPS polyp extension..

[ScubaSteve]

I've always wondered about this too, particularly in regards potassium dosing and PE. I've always been suspect that K makes the polyps extend by a physiological response rather than their own natural accord as potassium, for most animals, regulates muscle responses and fluid pressure balances between tissues. So dosing K might just be causing them to puff up like balloons... but really I don't know that for sure, so at this point I'm talking out of my a$$.

As for some colonies having PE and some not... I am suspecting an irritant, though figuring out what that may be could take forever. I'd venture to say it's probably sand that is bothering them.

Since I've been curious about this as well, I tell ya what... I've got some time to kill today while waiting for an experiment to finish. I'll dig into some journal articles and see if I can't get some sort of definitive answer.

[Aquattro]

Originally Posted by ScubaSteve

I've got some time to kill today while waiting for an experiment to finish. I'll dig into some journal articles and see if I can't get some sort of definitive answer.

That would be great. I too suspect the sand, it's really turbid. I picked up a grounding probe and some K, I'll see what that does later this afternoon. I found a way to get the sand out, so that's the next step.

[lastlight]

Originally Posted by Aquattro

I found a way to get the sand out, so that's the next step.

You've got your significant other working the 5g buckets? Tsk tsk!

[shootingstar]

Originally Posted by lastlight

You've got your significant other working the 5g buckets? Tsk tsk!

Bwahaha....

step 1) show s/o photo of bobbit worm
step 2) tell them the last person you got frags from (insert name) has just discovered one in their tank
step3) tell s/o there are most likely eggs in your sand bed that will hatch in about a week.
step 4) in a few days admire your spotless tank with the nekkid bottom.

insert beer where required.

[ScubaSteve]

Ok, so this is what I've got so far...

All corals have some mechanism to remove sediment and debris from their surfaces. Larger polyps exhibit 'twitching' mechanisms, whereas small polyped corals tend to have a full retraction of the polyp, leaving a relatively smooth skeletal surface which currents can easily blow sediment off of. This same response is also triggered by irritants like little red bugs so, if your polyps are continually not opening, it is most likely the turbidity of your water. Though it makes me wonder because my turbidity is also pretty high and my polyps couldn't be hanging out any further. No little bugs or AEFW?

I also found that corals with poor health (for various reasons) would tend to not extend their polyps.

But this is all stuff we kinda already knew....

In terms of potassium, corals definitely have a response to it as noted by several researchers but no one has really offered a difinitive answer on the matter. I did find that potassium DOES regulate pressures within coral membranes but I can't actually say that is what is causing the polyp extension. The explaination offered by a number of researchers that K is a limiting nutrient and that corals exhinited better health on its addition. They observed (cut and paste directly from the document):

- better growth of all photosynthetic organisms,
- more polyps at SPS,
- intensified branching of SPS,
- less „asthenic“ growth of branching SPS,
- intensified colors of colored corals,
- often a higher demand of macronutrients, due
to the increased primary production.

Unfortunately, no one knows why yet...

[lastlight]

My watchman frequently puts plenty of fines into the water column and I also have great PE. I was originally kidding about the sand but under the right circumstances who knows?

[christyf5]

no sandbed here but my fish crap a lot so I might as well call it turbidity PE has always been good (especially with the wavebox) and I had no PE when I had a sandbed (granted, PE was the least of my problems when I had a sandbed). I found when I dosed K I got better colors but I don't remember getting any better PE than without dosing. I'm thinking about taking up dosing again just to see if it does anything.

[Aquattro]

Just added the grounding probe and some K. We'll see what that does. If I get better colors, I suppose I'll have to live with it :P

The water column is actually pretty turbid, to the point you can see a solid beam of light from my PFO reflector. I can well imagine that the suspended particulate could irritate the corals.
The sand has to go anyway (I've got the use of a large filter to recycle the water), but the probe or K could also do it.