Zoa heads retract into tighter mat, head size shrinks. Normal behaviour with increased lighting?

[Northern Flicker]

Hey all, a couple of my zoas used to have rather large heads, and they had long stalks. Specifically my Red People Eaters and my Illuminatis.

I always thought they wanted more light - stretching with any photosynthetic organisms seems to point to this conclusion. I added a 2nd AI Prime over my 24x19" footprint tank. Since then, the heads on both have shrunk down by about 40%, and they now have no visible stalks. Instead, they form a very tight mat.

My question is whether or not I should see this as an improvement or a warning sign. To me, they actually look much nicer now, but they are getting very high levels of par (est. 250ish). The colours are very vibrant otherwise. They haven't put out a new polyp in a couple weeks, since updating the lighting situation, but I also don't want to keep moving them around too often.

 

[steveschuerger]

Definitely the amount of light. Maybe cut the % of light being put out. Two lights put out quite a bit more light than just one. I’ve had to fiddle with my larger tank a fair amount to find a light setting balance that all the corals would like. The nano is still finding its lighting “sweet spot” as well. I’d probably try to slowly back tread to about 180-200. They also could just need a little more acclimation time. But if they’re on the bottom of the tank, that’s pretty high par.

 

[littlebigreef]

As with all corals you make compromises when keeping softies (zoas), lps, sps all together in the same reef. Many zoanthids - like RPE, bam bams, scrambled eggs, rastas and so fourth - can tolerate a large range of par hence, why they tend to do so well for most people.

I'd say the law of diminishing return starts to kick in around 150 par and that's where you begin to see smaller polyps, tighter growth, less polyp extension. In my trough the highest par is 150 on center and around 80 at the wings. Some strains absolutely do benefit from higher par to bring out speckling, certain colors etc. But, for the most part, the vast majority do well around 130par. Coupled with that is the old adage that form follows function. Zoas are heterotrophs and need a certain amount of nutrition. When polyps are contracted and small due to high part it limits their ability to catch food.

My recommendation would be to throttle way back on the lighting.