Red Mythrax Crab: Zoa Eater?

Zakary2003 · Nov 13, 2023

I just bought a few new zoa frags and some of them are doing great, but one frag only has one of nine polyps open. Scratch that. One of eight, because one polyp is gone. I have a red mythrax crab and he was hanging out on the rock with the zoas on it today. Can they/do they eat zoas? What are the odds the zoa polyp coincidentally fell off or died unrelated to the crab? I've only seen him mess with my candycane coral, and that's only because he accidentally grabs tissue when trying to clean the skeleton. He's also irritating my 2 new duncan frags, but i don't think he is actually eating them. This isn't the first time I've mysteriously lost corals, but I though I removed the offenders already, who were a large hermit crab and a king crab, both caught in the act. I'd love to seperate him until the new corals seem open and healthy just to be safe, but I can't catch him! My whole structure is glued/epoxied together so it would be very destructive to forcibly remove him.

LiverockRocks · Nov 13, 2023

Zakary2003 said:
I just bought a few new zoa frags and some of them are doing great, but one frag only has one of nine polyps open. Scratch that. One of eight, because one polyp is gone. I have a red mythrax crab and he was hanging out on the rock with the zoas on it today. Can they/do they eat zoas? What are the odds the zoa polyp coincidentally fell off or died unrelated to the crab? I've only seen him mess with my candycane coral, and that's only because he accidentally grabs tissue when trying to clean the skeleton. He's also irritating my 2 new duncan frags, but i don't think he is actually eating them. This isn't the first time I've mysteriously lost corals, but I though I removed the offenders already, who were a large hermit crab and a king crab, both caught in the act. I'd love to seperate him until the new corals seem open and healthy just to be safe, but I can't catch him! My whole structure is glued/epoxied together so it would be very destructive to forcibly remove him.

Place a glass in the tank leaned against rock. Add a piece of shrimp or meaty morsel to bottom of glass. Red will fall in and be unable to climb out of the glass.
Then you can sump it or give away.

Jeroen1975 · Nov 13, 2023

I guess if there is nothing left to eat, even mithrax will eat what they can get.
I would try feeding it, but I also have to say I have the green type and haven't seen them eat coral...

Zakary2003 · Nov 13, 2023

Jeroen1975 said:
I guess if there is nothing left to eat, even mithrax will eat what they can get.
I would try feeding it, but I also have to say I have the green type and haven't seen them eat coral...

There's no shortage of food at the moment. I don't have a bad hair algae infestation, but there are a few clumps around that he hasn't touched. I also feed the frozen green cubes (emerald feast or something) and he usually gets quite a bit of that. I'm worried he's trying to clean the polyps but is damaging them instead.