I have caught my emerald crab several times hanging out on an SPS coral (acropora digitata I believe). I can't tell if he's eating polyps, but should I assume so?
If so, then um, I have two emerald crabs for sale, real cheap
I got them to help control valonia. The valonia is way down, but unfortunately, I took several anti-valonia meaures all at once so it's hard to know what caused the decline, but I'd like to give my crabs credit. Have they overstayed their welcome?