Tiny white crab living in Acropora - ID?

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BigKahuna

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I've had an Acropora frag in my tank on the sand acclimating for a bit and just noticed a tiny white crab living in the middle of some branches. He's probably less than a cm across and he's almost pure white with a black band with some blue highlights between the two halves of his shell. Best I could come up with is he might be a Houskeeper Crab, which might make him one of the few good crabs but I'm not sure.
 
Thanks, that looks 100% to be him. I'm kinda relieved, he's a cute little bigger and I hated the idea of banishing him to the sump ;)
 
Here is a little information on guard crabs that i took from an article. If you would like some background information, continue to read.

Guard Crabs
"Protection from predators is not the only benefit that these crabs provide. The activity of the crab between the coral branches has other positive benefits to its calcareous host. When it moves among the branches and feeds, the crab helps clean its host of sediment and also promotes irrigation of the tight spaces in the coral colony with "œfresh" (oxygenated) seawater. This will increase the coral colony's rate of growth and increase reproductive output. Studies have shown that when crabs are removed from their host Pocillopora species, the coral produces less mucus, the polyps are more likely to disintegrate, and there is often massive tissue exfoliation. Another study demonstrated that bleaching was a more common phenomenon in coral colonies that lacked crabs than those that hosted symbiotic crustaceans.

The keeper of Pocillopora and (to a lesser degree) Acropora corals should take careful note of these findings. While these coral colonies may survive in an aquarium without their crab partners, they may grow more vigorously and exhibit more natural growth forms when these crabs are present.

The coral provides the crab with shelter and a source of nutrients. In 1967 scientists figured out through stomach-content analysis and aquarium observation that crabs in the genera Trapezia and Tetralia feed on the mucus of their coral hosts. The presence of guard crabs in pocillioporid corals has also been shown to stimulate the coral to develop special lipid-filled fat bodies that the crabs will feed on. These excess lipids are apparently not needed by the corals but help the crabs survive.

These crabs are adapted to feeding on coral slime. The end of their appendages have comblike bristles, which they use to brush and irritate the coral polyps to increase mucus production. These bristles are also used to collect the slime and associated bacteria. When the mucus is transported to the crab's legs near the head, the crab cleans them of the mucus with its mouthparts (it's like the crab is licking off its fingers!)."
 
Yes, the acro crabs only eat coral mucus, and they don't hurt their host in the process, they even benefit it. They stimulate the protective mucose and clean the coral from detritus and some pests.
They don't leave the coral were they live, and if they do, it's to go to other similar acro or because they have found a mate.
OKDOHK said:
The presence of guard crabs in pocillioporid corals has also been shown to stimulate the coral to develop special lipid-filled fat bodies that the crabs will feed on. These excess lipids are apparently not needed by the corals but help the crabs survive.

These crabs are adapted to feeding on coral slime. The end of their appendages have comblike bristles, which they use to brush and irritate the coral polyps to increase mucus production. These bristles are also used to collect the slime and associated bacteria. When the mucus is transported to the crab’s legs near the head, the crab cleans them of the mucus with its mouthparts (it’s like the crab is licking off its fingers!)."
Click to expand...
 
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Ya know It's funny reading that...I had a nice acro colony with one of those crabs, then the crab went missing. Maybe my indigo dottyback had a feast. anyway the acro bleached within weeks after that.
 
Duna_ said:
Yes, the acro crabs only eat coral mucus, and they don't hurt their host in the process, they even benefit it. They stimulate the protective mucose and clean the coral from detritus and some pests.
They don't leave the coral were they live, and if they do, it's to go to other similar acro or because they have found a mate.
Click to expand...

I know but I'm just worried if it would, out of self defense or defending it's host, kill something like a bumblebee shrimp.
 
Calappidae said:
I know but I'm just worried if it would, out of self defense or defending it's host, kill something like a bumblebee shrimp.
Click to expand...

Anything could conceivably kill anything else. These are wild animals. Your shrimp could also die suddenly for no reason. How many times do people have to tell you the crab is safe and good for your tank and coral?
 
Aw, so cute! Little black-masked cutie.
They probably have a planktonic larval stage, which means it would be exceptionally difficult to keep the larvae alive until they settled. I doubt you can breed them.
I don't think that little guy is a threat to any shrimp, even tiny ones. They'd have to be his size or smaller for him to severely injure them, and since he's going to stay in there and probably just wave his claws at intruders, I doubt he'll ever encounter one.
 
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