The good the bad and the ugly acro crab thread

trueblackpercula

New member
Hi all
Can we start a good Sps acropora crab Vs bad acropora thread. It's amazing to see so many always ask is this good or bad, and some are killing crabs without not really knowing if it was really bad. Also with the spike of AEFW and red bugs Etc. I would like to know if those with good crabs have any pest that the crabs host. Well I hope this turns out to be a helpful thread as I am starting to think that these little crabs are more good to the health of our acroporas then most realize.
How know maybe this is the natural cure to AEFW and red bugs.
Thanks
 
Having spent many years stocking wild sourced SPS i have found that 75% or so of acros, pocils and stylos come with a resident commensal Trapezia or Tetralia sp. crab. I currently have at least 10 living in various SPS, some have been moved when others decided the digs looked better and evicted the resident who then finds a new SPS. I watch them remove detritus and anything caught amongst the colony branches and i have never seen one that has been anything but beneficial and extremely cool to watch in my reefs. I see their molts quite regularly blowing about the sand bed so i know they're doing well.
There is a dirty brown crab of a similar small size with banded legs and fine hair all over the body that i have removed about 10 times over the years from new SPS. In every case the crab was observed to be actively feeding on the living tissue of the coral in an area displaying tissue loss.

This one....

IMG_0730_zps2b1a5983.jpg


I found what i think is a red porcelain crab a few weeks ago at night on a monti, never had one before so i'm only going off similar pics on the net for id but since there was no damage the next morning i let him be and he has since been popping up all over the place - he appears to eat algae only so i see no point in 'killing him to be safe'
 
biggles has provided solid information. Anything in the Trapezia and Tetralia genus is considered beneficial. I have never seen the crab biggles has provide with a solid id, but do know they can be found on sps corals. Perhaps a type of Chlorodiella? Also, another species to look out for is Cymo genus. These guys are also considered not good for sps corals.
 
Well this is amazing information and is we can document with some photographs I will help users like myself who don't know all the Latin names you are posting. I am very excited to see that these crabs are a plus. I always just dip my sps and they fall out dead, now I will need to start identifying the good from the bad before dipping. Let's hope others chim in with there pictures and see what experience th are having.

Thanks for all the good information this far.
 
The following link has a great selection of pics of commensal crabs along with various other species and is a good reference for anyone who hasn't had much experience with keeping these little guys rather than killing them during the dipping process - they're a little bonus not something to be rid of imho. :)

http://www.chucksaddiction.com/hitchcrabs.html
 
Here is some general information on sps crabs.

http://www.fishchannel.com/saltwater-aquariums/reefkeeping/guard-crabs.aspx

Trapezia and Tetralia crabs are smooth, no hair. An easy way to tell the difference between the two genus are the claws. Trapezia have claws of equal size. Tetralia have one claw larger than the other. A general google image search of both names should provide many photos of each genus to compare to sps hitchhikers. Maybe some reefers can provide some of their photos.

Trapezia cymodoce tend to be the most common type of Trapezia hitchhiker. They are normally found on Pocillorpora corals.

http://www.poppe-images.com/?t=17&photoid=924106

Tetralia nigrolineata is likely the most common Tetralia hitchhiker that we see. Very famous for the black band across the eyes.

http://www.flickr.com/photos/the_three_p_romblon/8219333039/

Also this one is about Cymo melanodactylus. The most common type of Cymo hitchhiking crab that we see. All crabs in this genus are small and hairy. These are not teddy bear crabs that many reefers tend to confuse them with.

http://www.digitaljournal.com/article/342836
http://www.reeflex.net/tiere/3069_Cymo_melanodactylus.htm

The other type of sps crab hitchhiker is in the photo biggles provided. They tend to have striped legs of yellow, white, and blacks bands. Many have a black/dark coloured carapace (shell), with black/dark claws. The carapace can also come in other colours (mix of white, yellow, black), but the common theme is dark/black colouration somewhere on the carapace. This doesn't appear on any other sps crab as far as I know. The banded legs are the best giveaway. These banded legs of white, yellow, and black are also common in the Chlorodiella genus which is why I think this could be a species in the genus. With no definitive identification it's hard to find any information on this crab species. I would take biggles word for it, with the information about these guys eating sps tissue.

I have also wondered if sps crabs would prevent or protect their host coral from red bugs or AEFW. I think it would make for a wonderful experiment. I have no answer here.
 
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This crab on first glance looked like a common small white commensal crab. With the naked eye it was almost impossible to tell but he seemed to be irritating the polyps a bit. After putting on the lights in the middle of the night and taking some macros of the little bugger...

Looks like he's got those ole' blue eyes…
8816584582_d7c0ffc08b_b.jpg


And hairy butt…

8816583456_0aaa2d3936_b.jpg


OKDOHK agreed with me that he was a baddie and probably a Juvenile Cymo genus crab. I removed him just to be sure...
 
Hairy=bad
Smooth=good
My LFS will give me as many as I can spot divers den sells them for $19.
 
I forgot i took a few pics of one of my Tetralia sp. crabs in his colony (think he's sleeping), has the black eye band/cream shell and is the commonest type i've seen out of perhaps 100 over the years - not a single one has ever been anything but a cool little bonus which although very shy most times, do acclimate to you and after a while they don't shy away when you approach the tank :)
I know there are lots of others with good closeups (unlike mine) of these little guys so hopefully a few others will post pics so everyone can feel more confident in saving them before using a dip on the coral.

q_zps12d27cb5.png
 
I forgot i took a few pics of one of my Tetralia sp. crabs in his colony (think he's sleeping), has the black eye band/cream shell and is the commonest type i've seen out of perhaps 100 over the years - not a single one has ever been anything but a cool little bonus which although very shy most times, do acclimate to you and after a while they don't shy away when you approach the tank :)
I know there are lots of others with good closeups (unlike mine) of these little guys so hopefully a few others will post pics so everyone can feel more confident in saving them before using a dip on the coral.

q_zps12d27cb5.png

Thanks for the amazing picture, I have had these on sps that I have bought. The problem is that after I dips for AEFW and red bugs they die. How do you manage to keep them alive after your dip process or do not treat before adding to your main display tank?
Thanks for the information and yes these little crabs are a great addition.
 
I don't dip my corals prior to adding them but it is very easy to remove them from a colony if you intend dipping the coral, just gently herd them out of the coral with a thin screwdriver or similar whilst holding the coral over a container of water and flick them into the water once you get them to the outside edge of the colony. Simply throw them into the tank as they'll swim surprisingly fast into the nearest coral for safety.
Always look closely if you're trying to save these little guys as multiple crabs co habit colonies quite often rather than just a single crab - there are two of the crabs in the colony i posted a pic of. :thumbsup:
 
I dont know...this is a picture of my pocillopora crab....I grew a 4-5" dark green pocillopora colony from a 1" frag. It was doing great. Then I added some sps frags and one had this crab in it. After a few days, it relocated to my pocillopora colony. Over a few weeks, the color faded to pale pale green, and after several months it died.

I bought a new 4" pocillopora colony (dark red / green) a few weeks ago from divers den. Well, that crab found it and has been in it ever since I got it. Over the last 3-4 weeks, the color changed from dark red/green to pale yellow.

All my other sps are doing great. Im starting to blame the crab. Would he survive in my refugium, or does he need a host sps to live?
 

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Dexters reef
That crab doesn't look like a keeper but I will let someone else with more knowledge chim in. Great pictures and I would remove him from the tank.
 
Trapezia cymodoce. Yes they can cause problems. If the coral isn't large enough or producing enough mucus for this crab species they can and will graze on coral tissue. They really need a much larger coral host than what this one is currently on. This would be the only Trapezia I would consider a potential problem. As trueblackpercula mentioned, if it's causing coral deaths than best to remove, and yes I do believe it would likely die in the refugium without a pocillopora host.

Though they do protect their coral host like no crab I have ever seen.
http://www.youtube.com/watch?v=9gpEcFrgE_U
 
WOW! I had no idea that crab could be that aggressive before watching the video. He always has his arms out ready to fend things off or grab food, and I've seen him chase away curious hermits.

Unfortunate that he is likely the reason for my dieing pocillopora, and that he will not survive in my sump. He does wander to a larger SPS that is near by and about 6" in width, he doesnt cause any harm or stress to that guy, but, he always goes back to the pocillopora which is obviously being stressed.

While I like the crab, it seems I should just move him to the sump and forget about him. Hes causing more harm than good at this point.

Thank you everyone for the help, I hope my pocillipora recovers
 
Has anyone test them against AEFW yet? By the way this thread has some amazing information.
Thanks everyone for all your help and time.
 
that little guy is a bad boy!!! hes not scared of anything... lol!! the rocky music was killing me...lmao.. hes little but hes tough!!!!
 
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