Emerald Crab (Mithrax sculptus)

This crab was originally enlisted to be a member of The Clean Up Crew and assigned to the Refugium Suite where its main objective was to scavenge the area for leftover Bubble Algae (Valonia sp.). Bubble algae has become a nuisance interfering with my established red macro algae growth. And after manually removing most of the offending algae, I found that it was impossible to remove every last trace unless I had the aid of a pair of tweezers. But, the prospect of singling out 100 tiny green globes and going in and out of the refugium 200 times was too daunting a task.

After acclimating the crab to my tank water, I dumped it into the refugium where upon it immediately took hold of the red feather algae and, as an example, began to show me how he plans to attack bubble algae.

Has its eyes on the red feather algae

"First, I take hold of the algae with my specialized pincers, then snap a piece off and place it into my....into my.....my crab mouth". "You mean, 'mandibles'?", I asked. He didn't answer back as he was happily satiating himself with a full serving of Prime Red Reef Algae. At the pet store, he had been plucked from a small tank containing several dozens of other Emerald crabs where the competition for food must have been high, so I took pity and didn't ask why he didn't go straight for the green globes on the other side of the tank.

A few days later, I espied from the top of the tank to see what he was up to. He crawled up on an Aiptasia anemone populated rock and used his pincers to randomly scrape and eat. Eventually, the pincer came across a small Aiptasia and seemed to react to it. "What's this? Is it spicy? Yes, a small one...mmm......How 'bout a bigger sample? YEOOOOWWW! VERY SPICY! HOT! HOT!" He crawled backwards into a corner far away from the infested rock.
"No, I did not purposely put that there because you didn't eat the Bubble Algae as I requested. So, stop staring up at me like that," I said and went to bed.

On an Aiptasia-infested rock

As I was about to fall asleep, I shot out of bed and thought, "an Aiptasia-eating Emerald Crab?!" Why, that's even better than a bubble algae eater! But, so far, I've only come across one anecdotal web link here. The guy wanted to grow Aiptasia for fun, but one day discovered all gone with the only suspects being: "a turbo snail, a few nassarius snails, two tiny hermits and an emerald crab". So, I guess we'll be 2 references (I only looked at the first 20) out of about 2,600 cross-references when you Google the terms "emerald crab aiptasia".

But, in reality, the crab would only be expected to pick at the pest anemone and cause it to spread even more! The nudibranch Berghia would be the best biological control, but that has its own issues.

Clearing an old plate coral of Bubble Algae (see new baby plates?!)

Update: The crab seems to have eradicated all the bubble algae, but not the Aiptasia, within its reach. Also, it probably waved bon voyage with a claw to the Chromis that was on R&R in the refugium. I found the fish's scales in the filter sock some time later.