Crab in Acro - Good or Bad?

[Beverly]

Have noticed a tiny white/clearish crab, with one claw bigger than the other, on the base of an acropora I bought last week for my 37g lit by a 175w MH. Is this crab going to harm my coral?

Sorry for what might seem like a very dumb question, but I have never kept acros before

[Willow]

sounds like an acro crab. good commensile crab that lives within acro colonies.

[Willow]

sorry i should have asked what your magnesium levels are first :P

[Xtasia]

I heard they were ok b/c they keep the acropora clear of detritus. I have one with one tan crab, and another with 2 whitish ones. All's good 6 months now.

Wet web media says:
Hello,
Are the small crabs found in Acropora harmful to the coral?
>>
Not generally... all else being equal they're of no consequence.
Bob Fenner

Reefs.org has more info...
http://www.reefs.org/hhfaq/pages/mai..._livestock.htm

I just bought a colony of Acropora/Pocillopora and there is a crab living in it. Is it harmful?
Chances are that the crab you have found will not be a problem. Crabs found in heads of SPS corals are usually of the Family Xanthidae. They are typically commensals which sometimes protect the coral from predatory fish or invertebrates. However, all of these crabs should be watched carefully as not all of the Xanthids are harmless - see below. Trapezia sp. (Family Trapeziidae) is usually found in Pocilloporadae while species such as Tetralia and Domecia (Family Xanthidae) are the typical residents of Acroporidae.(Delbeek and Sprung The Reef Aquarium, Vol. II, pg. 324). In the experience of the author and other reefkeepers that the author has conversed with, hairy brown crabs imported in SPS colonies tend to be harmful rather than commensal, while the tan, smooth shelled crabs like the one in the above picture are peaceful, well-behaved residents.

HTH

[Chin_Lee]

Originally Posted by Willow

sorry i should have asked what your magnesium levels are first :P

almost made me spit out my coffee!!!



Beverly, keep in mind if you ever treat with interceptor, your crabs will not make it. If you need to treat with interceptor, try to get them out of the acro which is almost near impossible depending on the size of the colony.

[Beverly]

Thanks Willow and Xtasia for the replies and the link My crab looks something like the one in the pic.

Willow, don't actually know Mg levels in my tanks. Has been awhile since I last tested chemistry in all our reefs How's the Mg in your tank(s)

[GMGQ]

Quick rule of thumbs on these hitch hiker crabs:

HAIRY = BAD
Smooth = GOOD

I found 2 smooth ones in my big Yellow/Green Porcillipora the next day after I brought it home

[Manny]

i have those crabs in almost every one of my acros and one in my milli. they seem to be harmless and i would seem to be under the impresion that they are benifficial because the acro is its home.

[muck]

Originally Posted by chin_lee

almost made me spit out my coffee!!!

Thats too funny!!

[Winters]

Well, I recently acquired an Acro piece with this crab in it:



It does look a bit 'hairy'. People have advised me that it's probably okay. Thought I'd get another opinion. I'm assuming this is what is considered "hairy"?

Take care!