Why do poyps open?

[emissary]

So we all know that polyps come out to play when the lights come on. What wonderful coincidence that this enables the zooxanthellae to get light and photosynthesize, thus produce a variety of sugars, amino acids, lipids to feed the coral. But what makes the poyps puffy? Say... we're talking LPS here.

 

I guess there might be two possible causes? The coral itself may in some way take water into the tissue, or the zooxanthellae may be doing something to make water flow into the coral through osmosis. Any thoughts?

[davelin315]

I think that it becomes puffy for a couple of reasons (neither of which are grounded in my own scientific knowledge, although one is based on what I've heard before). First, I think they become puffy for the reason that the more they expand the more light they can absorb. If you have ever noticed that things such as mushrooms expand to outrageous sizes when water quality is good but lighting is not as great, this is evidence of this. Also, when they are placed under too much lighting they tend to withdraw so as to not get burned. I think that they optimize surface area and exposure to light by puffing up.

 

The second, not as backed up theory, is that they puff up to pull off from the skeleton a bit, perhaps in anticipation of budding or splitting. Not sure of this, although I have seen corals that swell up because they are looking to drop a bud somewhere.

[emissary]

I see what you're getting at on both points. But I think I am not explaining myself well. I understand the logical motivations to some extent of why a coral would need/want to do this. But ... although corals have a nervous system of sorts, they don't have a brain. There is no "hmm, I should puff up" thought. Unlike say, a cow, or a college student, which might think "mmm grass."

 

I figure there's got to be some kind of chemical process that incites change in the organism. So with a raisin, you throw it into salt water and it expands. Is there something that happens when the light comes on that triggers water to flow into the coral through the tissue? Hmm... I guess the polyps could swallow water into the gut directly...

[davelin315]

Photosynthesis. Same as a flower opening up in the daylight. As it's systems get moving, so do fluids. Energy is being created so the cells are in action.

[Lee Stearns]

light receptors trigger the opening - similar to the receptors on a clam- they sense it though they do not have "eyes"

What about the reverse- sending out thier feeder tenacles at night because that is when all the little bugs come out and about swimming, predators are less. Blastos, candy canes, trumpets, acans- have thier feeder tenacles all bristling out when the lights go out. Though if I feed cyclopese with golden pears and selcon in the daytime I can sometimes coax some of thier tenacles out- so they are "smelling" as well.