Xenia question

[nrs98001]

Hello Anthony,
I just read your article posted on the reefcentral homepage about xeniids. I enjoyed it very much. I did have one question based on my own experience with my Xeniid colonies (I thought they were elongata since that is most common, but they really look a lot like the Cespitularia pictured in the article - I know, I know :wink: They glitter when I shine a flashlight on them though). In the article you mention anecdotal evidence that under low light xeniids tend to stretch out, and under bright light they will contract early in the day. If I understood you correctly, I think I see both behaviors in my xeniids. My lighting is 4x96W PCs (2 10K, 2 Actinic 03 from hellolights) and the corals are all within 5 inches or so of the surface. For the first six hours of illumination the colonies are all stretched out to surprising proportions. Then after that, they scrunch up so tight that they're a fraction of the "daytime" size. On the surface this seems to suggest that my lights are too dim, but that the corals have had their fill after 6 hours? It just doesn't make sense to me. Do you think that, like pulsing, many other factors influence contractile behavior? After all, it must cost ATP to contract to such a fantastic extent. I know there's nothing to really answer here, I was just wondering if you had any comments. Thanks, and keep up the flow of literature - as soon as I buy a new mak4, my next purchase is reef inverts vol 1!!

[Anthony Calfo]

Very good questions and observations my friend. Indeed, there is no clear answer yet in this complex medium/dynamic of aquarium and reef science alike.

I have to speculate a bit about the possibilities in part for lack of more info about your system.

For consideration, and in contrary opinion:

A) if illumination is the reason for early contraction... then we could argue that the quality of light (lamps new? less than 6 months old) and good clarity of water (regular use of carbon, chemical media and or ozone with water changes?) with placement at such shallow depth (5"/12.5 cm) is allowing these corals to pass their compensation point with photosynthesis early in the day.

If instead, you are not faithful about water quality/clarity (less than weekly water changes and changes of carbon/the like) and/or the lamps are not fresh (over 6 months old) and/or the bulbs are above 3" off the surface of the water (rendering the shallow water depth placement of the coral somewhat moot... do note here how important it is for all fluorescent lights to be less than 3" off the water to be effective) then we might argue that

B) the corals are not contracting early in response to light.

If B), then we might speculate they are retracting in response to nutrient levels in flux (due to systematic feeding of fishes/corals and/or skimmate/skimmer activity)... or perhaps related to weak buffering in the system that tenders a flat ALK (pending the disolution of carbonate materials like aragonite later or regular dosing of supplements at evening/night.

Of course, it may very well be none of the above :D

I think I have effectively said nothing new here. Ha!

Well... food for thought in different sentence structures.

WIth kind regards, Anthony

PS- and working to finish volume 2 of that NMA series for release later this year :)

[nrs98001]

After some more thorough examination, I am pretty sure what I have in my tank is Xenia elongata. If you have a moment, you can see if you agree (www.freshwater-aquarium-fish.com/images/xenia.jpg). Just because I find this interesting, I will post some more information - please don't feel obligated to reply. I know you are busily writing and I don't to delay the new book :D

My tank is a 90gal AGA with the corner overflow. I have a homemade acrylic sump (~15 gal of water, 30gal cap.) with an EV-120 that I never have quite gotten dialed in right. The cup fills to just below the auto waste collector fitting every 5 to seven days. Not much skimmate, but it is jet black to greenish and very stinky. I also have a weak return pump that seems to be doing alright for the moment (rio3100). In the tank I have a maxijet (295gph). It isn't much water movement, and it's all laminar. I am trying to work out how to build an in-the-canopy closed loop to solve that problem. The lights are as I said in the last message (384W). The bulbs are about 5 months old and sit about 6 inches off the water surface. I know PCs should be closer, but the way my canopy is built I wasn't smart enough to figure out how to do that. There is a 5in aragonite DSB that is starting to stratify and turn funky colors (mostly red and grey). There are small (2-3mm) bubbles that I can only hope are N2 and not H2S! I change 15gal every week without exception, and test every 2 weeks. NH3, NO2 are always undetctable with my SeaChem tests. NO3 has never been above 5ppm. pH is on the low side - 8.1 - 8.3. Alk is always either 2.5 or 3meq (but I don't like the kit, RedSea) and Ca is always 450ppm. There is no detectable phosphate or silicate, and no rampant algae (a bit of valonia around). Iodine is 0.04-0.06ppm. I run carbon as a precaution against allelopathy between my zooanthid colony and the zenia (changed every 4 weeks). The water is always crystal clear.

Given that my lights are too far from the water to be totally effective, I guess your nutrient flux explanation makes the most sense. I routinely feed a small pinch of prime reef in the morning and a good dose of home-made frozen food at night (brine shrimp, silversides, krill, nori, and selcon all blended up). I feed this through a 10ml serological pipet (I work in a lab). Some is targeted to my zoanthid colony, and the rest goes right into the mouths of my fish (6 green chromis, 2 A. ocellaris, 2 N. magnifica, 1 C. strigosus, 2 G. oceanops, and 1 yellowtail blue damsel.) They have actually been unintentionally trained to peck at the pipet to get food. Now if anything goes into the tank (net, whatever) they all immediately start pecking at it! Anyway, this a pretty regular flux of nutrients into and out of the system. The xenia do always seem to close down about 1 - 2 hours after the feeding. Whether this is due directly to the nutrient wave hitting them, or to the cessation of all skimming activity I guess we will never know. For what it's worth, these xenia are kind of lazy pulsers. I think you are right when you say that this isn't a reliable indicator of health though, because they have spread themselves across the entire top of the tank. The bottom 2/3 is devoid of anything but nice purple corallines. (I hope to get some shrooms at the boston reefers meeting this weekend though). Sorry for the long and largely pointless email. I only hope it was as interesting to read as it was to write.

[Anthony Calfo]

The first thing to do would be to change the feeding time(s)and see if the Xenia respond to it.

Another interesting note, as Xenia does not have developed aspects for digestion of organismal captured prey... I wonder if they are not respoding to the clotting/clogging particulates in the water? We see this with other corald exposed to undesired/unnatural prey/particle sizes/feedings.

Their retraction could be in wait for the food storm to die down :P

Just random speculation on my part.

FWIW... in my GH with blazing natural sunlight, the Xenia elongata colonies were rarely retracted... and I never feed particulate food to these monospecific cultures. That doesn't say much... but it is consistent with the line of thought here... and it would be interesting to see if you temporarily stopped your slurry feedings (days) if the Xenia stayed open longer or did not contract at all.

kindly,

Anthony