Friend or Foe

Fantastic resource Chuck. Thanks. Will be back. I realized after posting my last pics that the crab was impossible to id at that distance. Can we confirm with this pic if it actually is of the Xanthid family.
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Liaquat i got this frag two months ago. Will try get another pic before it was fried, so you can see what it looked like before. From memory it always had this green base. It is really recovering quickly and is beginning to recolonate dead skeleton.
 
I'm confident thats its a Xanthidae species, although I would have liked to have seen its claws a bit closer. If they look like these, then it could be a Mithrax species, which is another family of crabs that I do not allow in my system.

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Chuck
 
charlesr1958 said:
it could be a Mithrax species, which is another family of crabs that I do not allow in my system.

Chuck
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Is there any particular reason why you do not like Mithrax crabs? They are indeed a useful critter in a reef aquarium as they are reef safe, it is a herbivorous crab and will spend most of its time eating through hair algae, bubble algae and other pest algae's. These crabs are commonly included in "cleanup crew" packs sold around the world.
 
Hi Dean - I think the main issue here could be, that the bigger the crabs' pincers, the more damage they can do - even though you might think that their main food-source is mostly algae.... imagine algae being on or close to a coral - that crab would not mind taking a piece or coral WITH a big piece of coral with it....

I have read that MOST crabs are omnivores - meaning that they are opportunistic feeds that could (in theory) develop a "taste" for coral meat....
The thing about "cleanup crew" crabs (hermits mostly) is that their little "pincers" are MOSTLY too small to do much damage to corals....
 
viper357 said:
Is there any particular reason why you do not like Mithrax crabs? They are indeed a useful critter in a reef aquarium as they are reef safe, it is a herbivorous crab and will spend most of its time eating through hair algae, bubble algae and other pest algae's. These crabs are commonly included in "cleanup crew" packs sold around the world.
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Dean- I think it just depends on the type of crab AND what corals you have. There are certainly many (maybe even most) that can get to be dangerously aggressive/carnivorous. But I think that the "emerald crabs" and even the "ruby crabs" are pretty safe (at least in my experience). They might steal food from a coral now and then, but I've never seen them pick at anything I didn't want them picking at.
 
i found one of those black clawed ones hiding in one of my rocks.Very shy might i add, possibly a mithrax.
Should this little fella be in my tank??I havent seen any issues although i would like him to chow some mushies, they are growing like wildfire at the size of plates !!!
 
Um, maybe shy to you... but just wait till you're not looking. ;)

Personally, I don't hate crabs, but the people who claim they're all inherently evil aren't entirely crazy. The truth is probably that MOST crabs are bad for reef tanks (in some way or another).
 
sihaya said:
Dean- I think it just depends on the type of crab AND what corals you have. There are certainly many (maybe even most) that can get to be dangerously aggressive/carnivorous. But I think that the "emerald crabs" and even the "ruby crabs" are pretty safe (at least in my experience). They might steal food from a coral now and then, but I've never seen them pick at anything I didn't want them picking at.
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Indeed, I was referring to the Emerald crabs.

I do think it is a bit unfair to label the entire "Mithrax" species as unsuitable for a reef aquarium when there are certainly one or two crabs from the species that are well suited to a reef aquarium.

Chuck said:
a Mithrax species, which is another family of crabs that I do not allow in my system
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viper357 said:
I do think it is a bit unfair to label the entire "Mithrax" species as unsuitable for a reef aquarium when there are certainly one or two crabs from the species that are well suited to a reef aquarium.
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Agreed... I love emerald crabs. They do get on my nerves every once in awhile when they climb on my corals during feeding time (not to "intentionally" hurt the coral, but just to steal food). But I've found that if I just "hand them" a big chunk of food, they'll grab it and run and hide somewhere (leaving the coral alone). It's kinda cute actually... you can almost hear them saying "mine! mine! mine!" as they run away with it. LOL... sorry, too many Pixar movies for me.
 
mekaeel said:
the only crabs that i feel safe with is a hermit crab.(exept the hairy leg one) the others just freak me out
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Are you serious? hermits don't freak you out? Have you SEEN what hermit crabs look like outside their shells?! :dft008: LOL
 
Any and all free ranging crabs with very few exceptions are omnivores, including the emerald (mithrax) crabs, of which can become a problem when they discover meatier items are to be had on the menu. While I have not seen the green "emerald" crab cause a problem for corals, they can and have gone after tube worms and many other inverts. Other species of Mithrax are known to have a thing for zoanthids. This species:

clingcrab7.jpg
When they get large or larger, will go after zoanthids, and a host of other inverts. I at first thought it was just a particuliar specimen but after having each and every one of them grow up and go after zoanthids and my feather dusters, it became obvious that its a family trait. Some species / specimens appear to be reef safe for some tanks, others...not. I won't risk it when there are other, and better herbivores of filament algae types. (scopas tangs and ring cowrys).

As per the clean up crew packages sold, I have issues with those as well. Hermit crabs - Not in my reef tank. Astrea snails - Our rocky habitats are not suitable for them. A great many of the species sold in such kits are those that are most easily grabbed up out of the ocean, which usualy means they were found near shore, of which I have yet to see any such near shore critters to be suitable for an invert dominated tank. Living near shore means they have to be tough to survive such conditions, that toughness usualy equates into " I can take down and eat just about anything I want". Or, in the case of Astrea snails, they are only ever found by me in the grass beds. Never out on the reef.

I also have to say that this is becoming extremely hard for me to post when a certain other parrots standard answers and I can not reply out of fear of not being able to remain civil. I think I'll have to go back to just lurking...lol

Chuck
 
charlesr1958 said:
Other species of Mithrax are known to have a thing for zoanthids.
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True, but this isn't always such a bad thing... lol I recall once in Pittsburgh, a PMASI club member went from store to store looking for sundial snails because his zoanthids were becoming a nuisance.

But anyway...

Regarding emerald/ruby crabs going after inverts, I don't think this is as likely to become a problem in well fed tanks. I have a lot of the ruby and emerald crabs (and am even trying to bred/raise them-- I actually have a small species tank of them), so I feel like I've "gotten to know" them a bit. And it seems to me that they're actually quite "lazy" animals. In my observations, they appear to prefer to scavenge than to hunt. Thus, this is why I think that in well fed tanks they're much less likely to become invert or coral predators.
 
Well Polly, I would not want to have a crab in my system that I have to purposely ensure its well fed to keep it from going after my other inverts.

Chuck
 
::shrug:: As they say... to each his own.

But for anyone who does like these guys (emeralds and rubies)... I actually make a separate food for mine. I use 5 different types of dried seaweed (from either an Asian or "health food" grocery store). Then I soak them in some of my regular meaty food. Once they're a little soft, I puree them in a food processor. I keep the mix in flats in my freezer. The crabs just go nuts for it!! :D
 
charlesr1958 said:
As per the clean up crew packages sold, I have issues with those as well. Hermit crabs - Not in my reef tank. Astrea snails - Our rocky habitats are not suitable for them. A great many of the species sold in such kits are those that are most easily grabbed up out of the ocean, which usualy means they were found near shore, of which I have yet to see any such near shore critters to be suitable for an invert dominated tank. Living near shore means they have to be tough to survive such conditions, that toughness usualy equates into " I can take down and eat just about anything I want". Or, in the case of Astrea snails, they are only ever found by me in the grass beds. Never out on the reef.
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True, I think in most instances most scavenger spieces are going to be hit and miss, with the real danger coming from the night time predators. I've had my fair amount of problems with hermits but the saving grace is that they are slow and easy to catch. If I find one hovering around my corals I remove it and send it back to the ocean.

For clean up crews I prefer Brittle stars.
 
DragonReef said:
True, I think in most instances most scavenger spieces are going to be hit and miss, with the real danger coming from the night time predators. I've had my fair amount of problems with hermits but the saving grace is that they are slow and easy to catch. If I find one hovering around my corals I remove it and send it back to the ocean.

For clean up crews I prefer Brittle stars.
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I love the mini-brittle stars! Do you have those too? (If not, I could try and send y'all some with the purple algae). With the big ones, you really have to pick the right species. Some are great, others get nick names like "green death." One aquarist who wrote into WWM once actually lost 3 fish to one of these monsters... :029:
 
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