Crabs and Acropora

Doctor Derp · Jan 18, 2022

Over the past few months, I've noticed a spot here or there on some of my sticks where it looks like something came along and took a small little bite out of the colony. Like, fish-sized mouth bites. Never more than one or two spots at a time, and never on the same coral twice. I don't keep any fish known to nip at coral, and definitely nobody with an appetite or the teeth for calcium carbonate. One instance had damage one 1/3 of the actively encrusting base, maybe 1-2mm of flesh and skeleton scraped away raggedly. Yesterday morning, I watched a scarlet hermit use his shell like a wrecking ball and grind the side off of a newly placed tenuis frag.

Fast forward to last night: I'm checking on SPS frags in the 50 lowboy, and I spot an emerald crab sitting at the base of a pink mille, using a claw to scrape out the tip of an axial corallite, flesh, skeleton, and all.

what the heck, guys?! I've seen murder hermits with my own eyes, but this is ridiculous. I'm about ready to yank anything bigger than a blue leg out of my sps systems.

T-J · Jan 18, 2022

I once had an emerald crab eating polyps. That's why they only live in my sump now.

Doctor Derp · Jan 18, 2022

T-J said:
I once had an emerald crab eating polyps. That's why they only live in my sump now.

I exiled the offender to the damsel / macro tank upon his capture. The rest of them like to prowl at night. I'll likely start removing them this evening.

SamMule · Jan 19, 2022

Emerald crabs seem to be hit or miss. Had some that were algae eating machines and never bothered corals.

On the other hand....

The one pictured above is eating the byssal threads of what was an otherwise healthy black/gold maxima clam....

Also have another pic somewhere of a hole dug into the stalk of one of my torches from another emerald.

Male, female, doesn't seem to matter. For me, they're not worth the risk anymore.