Please allow me to share my experience and research over the past few years with this issue.
I am 100% certain that anthropods eat zoas. I have a very small 5 gallon desktop aquarium and I have lost dozens of zoas to pods. With my own eyes I have seen the anthropods eat a ring around the base of the Zoas until the Zoa heads detached and floated away! Utter Chaos Zoas have truly lived up to their name in my tiny tank. After such a loss I explored the issue intently. Here's what I've discovered through research and primary research and experience.
I believe what happens is they establish off over feeding and over populate in a tank. Some varieties get a taste for Zoas. I have seen them eat other corals, but Zoas are their major preference. These anthropods do not just stop at the dead tissue. After months of wondering why my injured Scolymia wouldn't continue to heal, I found four very fat and plump pods living in the base of the coral - in quarantine! At night the pods would eat a ring around the apron of the Scolymia. There were multiple Zoa species in the quarantine tank too. Strange and frustrating!
This is a similar feasting pattern anthropods have on Zoanthids, where the mat of the zoa base is the first attack, shuffling along the edge of the mat as they eat. They can complete entire rings, as per my experience above.
Other corals where they devastated the tissue are Favia, GSP, Acanthophyllia, Blastomussa. Anything soft has been witness to the voracious appetite of pods. They have tried to eat Palys. It seems Palytoxin is a great natural defense. Kenya Tree and Riccordea and Yuma mushrooms are also unaffected.
This variety of anthropod appears to be a different species than the common "good" anthropod. Their sizes range from 1mm to 2cm and are able to hide in the tiny crevices of any porous surface. Several comments over many forums in my research describe how much larger they appear than another reefer's experience.
Wrasses are their natural predator I am told! But try keeping a wrasse happy in a 5 gallon barebottom with 6 lbs of rock! I've tried to starve my tank but it has been impossible - other species of life must eat, too, IMO. I built an emergency quarantine tank out of a plastic food-safe container and I dip every 3-5 days. The pods still exist as some coral structures are very porous as in the base of a Scolymia. Finally, in a small mug I hand dipped 20 individual frags with a small pippet and knocked out the last few after two months of quarantine.
My proof is that they will turn to the colour of what they eat - purple (zoas), pink (Vitalis pellet food), red (favia), or green (favia). They are well fed when they are dark and plump and go pale and transparent when fasting. This variety of anthropod can handle months without food in a small bare-bottom tank. They will sustain on any detritus until a preferential food source is found.
Many established reefers will swear that pods only eat dead tissues - but after 10 years in the hobby and my own disaster with them the conversation needs to change. Pods definitely can get a taste for, and wreak havoc on, zoas and soft tissues in general.
