Friend or foe? Acro crab

[Freed]

Hi Anthony, I've talked to you a bit on wetweb and have your book that you autographed for my fiancee a couple of years ago as an X-mas present for me. Thanks. Please see the attached photo and guide me as to whether or not the crab in the picture is a friend or foe to this acro or other acros. I wouldn't want to keep it if it were endangering anything. Thanks.

Acro crab

[Anthony Calfo]

cheers, my friend

reliable IDs by photo only are near impossible, alas. Readers of this forum will see that statement repeated very often. I will not speculate or give false hope/fears on image IDs.

But no worries... with this coral being properly screened in a quarantine tank, you can observe the crab's behavior in that one month period without the risk or fear of those aquarists that (sigh) put animals into display without QT have. Here, you have no risk that this creature will spread to other acros, reproduce or carry disease, pests or pathogens in with it.

And if it does nibble on some polyps, well... it is quite obvious it is the only predator in a bare bottomed QT tank (no suspect other display fishes, etc).

On the rare chance that this coral is not sitting in a QT tank ... do get it into isolation for observation and then read the latest issue on quarantine in this months issue of reefkeeping.com e-zine.

How's that for transition?

kindly

Anthony

[Freed]

I had the coral in QT for at least 2 months and thought the crab was a good acro crab. I was just watching him a little bit ago and witnessed him break off a tiny piece of the coral where the polyps extend from(don't know the correct terminology), will call it the "nub" growing from the side of the branch and put it in his mouth and roll it around and pull it back out. Then put it back in his mouth. The ends of his main claws are orange and are also cup shaped, not pointed, just like an emerald crab but he looks nothing like an emerald. I quickly removed him and put him back in the QT tank. Hate to kill him. No damage luckily has happened to the coral as he has been living on/in it for around 4-5 months.

[Anthony Calfo]

excellent procedure my friend.

And as an explanation for this crabs behavior (seeming safe then unsafe)... most crabs are fairly opportunistic. A look into my history of comments on crabs reveals a hard line. None - ever to be safe in reef tanks with sessile inverts (and small fishes). A majority of crabs are opportunistic predators. Varieties like Mithraculus will behave eating nuisance algae so long as the nuisance algae is around and easy. When that food gets scarce... they change gears and start looking funny at the scooter blenny and eventually the yellow tang

Anthony

[Freed]

Yes, have read your views many times before my friend. What is the "nub" on the side of the branch I speak of?

[Critter!]

Hey, its time somone said: NICE Coral!

[weatherson]

Yes, I agree, that's a very nice coral. The bad news is... it has Red Bugs. Did you treat the coral prior to adding it to your tank? I've had good luck with a Lugol's dip at removing them.

Joseph

[dieselfish]

wow , thats not a crab its a tarantula. that doesn't look like the crabs hosting in my acro's.

[Freed]

I took this at the same time I did the other pic but with a flash. They show up better with this pic. Are they harmful? I can see them with my eyes when looking down from the top and they are only the size of a pin point. Is this what you are talking about? Is that how big they actually are? Won't my six line wrasse take care of them? Do I need to worry? Anthony, can you add any insight to these "red bugs"? Are they harmful?

[weatherson]

Yes, they are harmful to SPS and that's how small they are. Do a search and you will find much information about them. If your sixline does eat them, he'll be worth size in gold.

Joseph

[DgenR8]

Many people have had success using a veterinary medication for heartworm (I can't remember the name) in the battle against the dreaded red bugs. It's very unlikely that your 6 line, or any other fish will eat them.

[MiddletonMark]

Here's my pics of Red Bugs


I found better coloration [esp blue/purple], polyp extension, and growth once I eliminated red bugs.
Not all Acropora were affected [at least equally affected] ... and I could only see them on a few even though more [IMO] were suffering from them.

Anyway, back to your corals ... but thought as your pic `matches' mine in terms of red bugs, maybe useful.

[Anthony Calfo]

the jury really is still out on these "bugs".

Eric B. et al. have found some/references to obligate species (as I recall) and clearly harmful ones... but also he/we see others (moreso) that are more of a nuisance (like acoel flatworms) than anything... lingering most times and at worst becoming opportunistic only after a while/somtimes.

Do be careful usung the insecticide if you do. I have heard this works very well for some folks, but it still concerns me (collateral damage). As Larry has suggested. Please do some exploratory keyword/phrase searches to find a consensus on the matter.

kindly,

Anthony

[JB NY]

To go back to the acro crab question.

Looking in my tank as well as a few others, I've seen more than a few different acro crabs. IME, the one pictured above does indeed feed on acroporids. Specifically the corallites. I'm not sure if the crab removes the corallite to eat the polyp, or if it's looking for tasty bits within the coenosteum. Eitherway, they don't do a tremendous amount of damage in a short time, so you have plenty of time to act. What I've done in my tank is keep an eye on them as well as the areas and/or branch that they are in. These crabs, if they are the same, will usually pearch themselves on the branches of your acroporids (most of the safer acro crabs will spend the majority of time deeper in the branches). Also, and more importantly, while on the branch itself you should be able to easy observe the crab removing the radial corallites. If you can see this happening I would suggest removing the crab.

[Bamm Bamm]

I just picked up one of these as well and another kind yesterday on two colonies I purchased.. Do they pose any damage to softies or LPS? if not I can banish them to my nano..

[Freed]

Originally posted by Freed
I was just watching him a little bit ago and witnessed him break off a tiny piece of the coral where the polyps extend from(don't know the correct terminology), will call it the "nub" growing from the side of the branch and put it in his mouth and roll it around and pull it back out. Then put it back in his mouth.

[Anthony Calfo]

Bamm Bamm, we just cannot say definitively what it will do. Beyond the fact that most crabs are opportunistic predators and variably a risk not only by specimen, but by month/day (available food)... we also cannot fairly make an ID and assessment based on a mere picture (or not).

My advice with all crabs (rarest exceptions... like the filter-feeding Porcelain crabs) is that the majority seen in the trade are opportunistic and omnivorous - posing a risk to small fishes, corals and other desirable invertebrates in time.

I very rarely recommend or use crabs in reef aquaria... yet I do so in other displays without vulnerable tankmates as crabs are fantastically interesting and utilitarian (good scavengers... then very thing that makes them a risk in reef tanks).

Anthony

[Bamm Bamm]

Anthony thanks soo much!!! I just picked up your coral fragging book btw can't wait to read it! I just setup the nanocube this afternoon I'll try and get that crab out and throw it in there.. I put a few SPS up high in the nano to try it out=)

[Anthony Calfo]

all good, my friend I hope you enjoy the read. And good luck catching the crab. Many tips and reports for catching here on RC in the archive I suspect. There are quite a few suggestions in the FAQs archives over at wetwebmedia.com too

Anthony