Recently I’ve been noticing my acropora pull in their polyps anywhere from slightly to completely after the lights come on. My other SPS (stylophora and the like) have no such issues. Everything is growing well and has great color. There has been no change in light intensity or anything along those lines.
What could be the cause? Any theories?
-Josh
Self esteem issues? I once met a girl at a bar that did the same thing. 
Sorry I couldn’t resist.
Does it stay closed while the lights are on or will it extend it’s polyps after a few minutes?
BoNg
For the most part they stay closed up. My millie’s have some polyps but certainly not what they’re capable of.
But like I mentioned, they’re all growing like mad. Little frags that have never grown in my tank are throwing out new branches every other day… just no daytime polyps. ???
It’s hard to say for sure, but a couple notes. Most corals will look differently at night then they do during the day. Many corals will stretch out at night to catch food and then tighten up a bit during the day when there is less zooplankton activity(aka “pods”).
My frilliest(furthest extended polyps/not a technical term) Acropora millepora extends like crazy right after lights typically go out. It does this wither the lights go off or not and it begins the further extension even before the lights go off. Corals seem to not only have a great internal calendar to spawn at the same time each year, but also know when sunrise and sunset is to be expected.
Something you might try if you have time one day. Leave your lights off for the first couple hours they are normally on, see if the coral has the same reaction.
Also keep in mind other critters besides your corals and the critters they eat act differently at different times of the day. Many wrasse that like to nip at coral polyps are not active during the night time. Could be your lights come up and your bored and hungry fish/shrimp/crab/whatever decides to nibble on some polyps?
Again it’s hard to say for sure, but just some random thoughts.
What kind of fish are in the tank?
When I get new corals they open during the day and close at night, after a week they do the opposite some stay open some don’t. A fey seem to have a polyp in a polyp one day and one night. I think theyre being fed enough by your light so they can rest during the day then at night they feed but that’s just my thought no data to back it up
I have a Melanurus Wrasse, but he only eats worms and such.
This seemed to happen out of nowhere… one day there were awesome full extension polyps and the next they were retracted. Hence the mystery.
I’ll do the morning w/o light today and see what happens.
Thanks for the ideas everyone.
Josh
if it is truely polyp retractions it could also be that a hermit crab had walked over them or a blenny perched on them for a moment. In our aquaculture systems we avoid fish that tend to perch on corals or adding any significant number of invertebrates. In general closed polyps are receiving less light and food and aren’t growing as quickly as extended polyps.
Always good to figure out what is going on and make sure it isn’t something more serious as well.
Are you familiar with “Red bugs” and other pests? (just to know what to watch out for) These could cause part of a coral to close up while the other part stays extended.
I don’t have any perching fish or crabs of any sort. I haven’t noticed any bugs or nudibranches and any flatworms were destroyed by the wrasse long ago.
All good suggestions though. I’m going to inspect everything again and maybe pull out my 30x jeweler’s loop for a closer look.
I’ll be turning my lights on in about an hour. Let’s see what happens.
5-10 minutes after the actinic lights came on, I still had fluffy happy acros. Soon after that they began retracting. By the time the leds came on an hour or so later they had pulled their ‘stuff’ in as usual. No fish were involved as far as I could see.
Also, I stared at all of my acros that were close enough to the glass for me to see the little ‘channels and tributaries’ (you know what I’m talkin about)… I didn’t observe any specks or movement that would indicate bugs. One of the investigated coral was a hawkins blue which I think would make anything like a redbug very visible.
But I’m still going to keep looking for .5mm critters that may not even be there… Oh, the paranoia!
Now, what does all this information add up to do you think?