I've had these zoanthids for 6 months or so. I feed once a week reef roids and noticed this week they appear to be only partially opening. Is something going wrong here or are they expelling waste?
I would lean towards unhappiness. I do see some portions expelling brown innards - is it brown slime or brown pellet looking? This is how you differentiate between zooxanthellae (slime) or poop. If it's the former, then they are are on the decline
Will you please provide your water parameters, up to date if possible?
Have you monitored this rock for any critters prancing about that are irritating them?
Water changes will typically help, I think 40 is okay, but not stellar. closer to the 20 range would put us at ease and allow us to divvy that out as a probable cause. Granted, if you've always been around 40 and saw no issues in the past, then you could do a lesser percentage. 40% will swing.
The only other value I'd like to know is what your phosphates may be and if you've changed anything in the past week or so? Any other additions, chemicals, etc?
With that said, I encourage you to wait it out for 1-2 days. I think that a big meal was had, and they're just recovering from Thanksgiving in June Use these 1-2 days to monitor the colony and look for any predators such as zoa nudibranchs, zoa spiders, etc.. - especially on the tops of them.
Zoa's are resilient, and I suspect you have some other healthy corals in there. If it seems isolated, then definitely invest more time into this colony. It's a nice one and a keeper! Rootin for ya
It us not uncommon to hear of emerald crabs picking at corals and possibly acquiring a taste for them. I unfortunately cannot give you personal experience as I've avoided them purely to reduce the risk alone. Just remember that emerald crabs are opportunistic feeders. Hey may have only began picking at them due to the health of the corals in decline and decay, or caused it. I would recommend that, if you can, remove the crab and place it in a sump or area outside of the display tank for quarantine.
I have moved the zoanthids to a private enclosure within the tank to keep the emerald crab off of them. I also cut / removed about 6 heads as they were hardly attached and seemed to be either dead or were partially removed by the crab. Any recommendations on what I should do moving forward here and do these look healthy? ALl other corals are thriving and bigger and brighter than ever.
Still have several polyps not opening per the pics below.