Normal Periodic Retraction vs. Damage Retraction?

[modernREEF]

First scenario: znp colony closes up periodically, but opens up fine a little while later (a few days/weeks), ie. one day they're closed, the next day they're open with full skirts.

Second scenario: znp colony closes up, starts to open up a few days/weeks later BUT the opening is very gradual, ie. one day they're closed, next day a little bit of oral disc, next a little more + a bit of skirt, next a bit more skirt, etc.
NOTE: by 'a bit of skirt' I mean a few 'tentacles' then a few more, not all the 'tentacles' out a bit, then a bit more - hope that makes sense.

It seems like in the second scenario, the colony closed due to some sort of trauma (chemical, not physical) and struggles to return to full strength.

Any ideas on the differences here? Is the second one due to a param. swing that, if corrected, allows the colony to slowly recover? Maybe they're been stung?

 

[A. Grandis]

Yep, could be irritation or chemical imbalance for both cases.
Some times even bacterial infections could recede, and the polyps would fight back.
Internal damage would do it too, like when we hit them by accident while doing maintenance...
So many things and variables for every particular system...
I don't think there is a straight answer for your question, but it is a very interesting subject.

Grandis.