Blue Leg Crabs Good For Reef Tank?

[RobbyG]

I have a 90 Gal tank with about 15-20 Caribbean Blue legs crabs, all small about 1/4"- 1/2" wide shells. At first I thought they where great scavengers, cleaning up all the left overs and hopefully any hair Algae. Lately I am not so sure, they don't seem to eat any algae and they are always plucking on my rocks. I am now wondering if they are eating everything that is alive on the rocks including potential coral growths. Do the negatives of keeping these guys outway any benefits?

Need some advice on this.
Thanks

[danoreef]

thats what I have inmy tank they always seem to eating something off the rocks

[AZDesertRat]

Nope, they love snails. You will soon find every blue leg sporting a nice new snail shell! The only crabs I have not had any problems with are Scarlet hermits, they have never bothered a thing.

[tangtang81]

they do love snails....however i have never seen them attack a snail unless the snail is laying on its back.

[danoreef]

I don't know why... when I add somethig new to the tank luckily I have a great success rate. although if I add scarlet hermit crabs I never EVERRRRR see them again????????

sorry I do not mean to go off topic.

[SDguy]

I have a very large Calcinus elegans that has never bothered a snail or anything else in the tank. The unidentified red hermit in the pic was also a model citizen, and very good algae eater (RIP )

[Aadler]

I have trouble when snails fall off the glass(trochus) with nassarius snails, they come right out and just rip the poor things to shreds. Blue legged hermits will take up a new home in snail shells, but i have never witnessed them KILL a snail to get the shell. but i have many snail shells laying around my tank.

[SFeST]

The only mean hermit I ever remember having was a zebra hermit that went after turbo snails. But that was just one, and I've had blues, scarlets and zebras all mixed at one time before and they all seemed to do about the same things and were all great at cleaning.

[RobbyG]

Ok but the Blue Leg is picking at the rock all day so is it basically killing any new life that might be growing like Sponge spores or coral gammets etc. Since they dont seem to eat Algae I figure they are eating something on the rocks.

[m2434]

I've never noticed them killing sanils as long as there are sufficient empty snail shells laying around. Some people insist that it occurs regardless. Personally, I have a 10:1 ratio of snails to crabs, so maybe that has something to do with it, not sure. I don't like crabs because they steal food from corals, but otherwise no problems here. If you don't have corals that require feeding such as plate-corals or non-photosynthetic corals, this wouldn't be a problem. Also, I believe if you have sufficient shells they won't bother your snails, but you may need a lot of shells.

[Kemo484]

I have a some blue legs, I keep a good amount of empty shells in my tank though. Knock on wood, I haven't had any of them attack a snail yet. I did have a zebra crab though that killed my fighting conch, so I took him back.

[RobbyG]

I assume that at this point no one is really certain if the Crabs are stripping the rock of all potential life. I think I am going to remove most of them before they strip my rock surgically clean

[Zatko]

Robby - for those blue leggedds to "strip your rock surgically clean," I would imagine you'd need quite a large number of them.

I've heard 1 crab per gallon of volume in the tank. I'd imagine it would have to be a tank loaded with live rock as well. Them actually causing any kind of damage to the rock (i.e. killing off sponges, coral gametes..) is pretty negligible. Your live rock should contain tons of little creatures, more than an ample supply of food for your corals, fish, and crabs.

Don't fret, these little guys may look like they are doing some sort of damage, but those are diligently working the algae that you cannot really see. If you are looking for more of a cleanup crew for detritus and excess food, go for the scarlet reef/red hermit crabs. They are a little bigger, but have a lot more color, and tend to be a little more active in my opinion.

One more thing - putting your hands in the tank consistently and moving things around is more of problem then those crabs. And if you are really concerned about them stealing food from corals and whatnot, use a turkey baster or a low flow power head and blow your rocks causing a small kick up of whatever is on the rock. A few benefits of this is corals feeding off the critters you've just thrown into the current, and also, corraline algae will grow where the sediment that you blew off once was. So more desirable algae and an easy/cheap way to feed your corals. But please do not over do this. Don't blow off every rock and expect a feeding frenzy (I would advise blowing off most of your rock prior to a water change, though). More than likely you will cause the corals to recede and possibly affect the oxygen exchange in your fishes gills.

Anyway, I went off on a tangent there. Hope I answered something.

[brickbreaker33]

are the reds okay though?

[Zatko]

brickbreaker33 - are you asking if the red leggeds are safe to be in a reef tank? Then yes, 100% safe. Some may be a tad larger than some would like and can cause some small corals to be displaced, especially frags not secured well.

[Cope]

I would stay away from the Zebras, They get huge and will kill all kind of stuff, knock over rock , corals
JMO
Cope

[vessxpress1]

Originally posted by danoreef
I don't know why... when I add somethig new to the tank luckily I have a great success rate. although if I add scarlet hermit crabs I never EVERRRRR see them again????????

sorry I do not mean to go off topic.

Because scarlet hermits seem to be mainly nocturnal. For me anyways. Not to say you'll never see one out in the day but you usually won't see them.

I was just thinking the other day about where all my hermits went including my scarlets. I never see a scarlet around anymore. I just happened to shine the flashlight around the tank last night and spotted 3 of them right away. I hadn't seen them in months.

And I've only got a 38 gallon!

[RobbyG]

Thanks Zatko on your advice I will keep a few and watch them for awhile. I will look into getting some Red Hermits and see how they work out. LOL one good thing about the Blue legs is that they are easy to remove, just put in a whole raw shrimp and within minutes they are all stuck to it like glue in a feeding frenzy.

Originally posted by Zatko
Robby - for those blue leggedds to "strip your rock surgically clean," I would imagine you'd need quite a large number of them.

I've heard 1 crab per gallon of volume in the tank. I'd imagine it would have to be a tank loaded with live rock as well. Them actually causing any kind of damage to the rock (i.e. killing off sponges, coral gametes..) is pretty negligible. Your live rock should contain tons of little creatures, more than an ample supply of food for your corals, fish, and crabs.

Don't fret, these little guys may look like they are doing some sort of damage, but those are diligently working the algae that you cannot really see. If you are looking for more of a cleanup crew for detritus and excess food, go for the scarlet reef/red hermit crabs. They are a little bigger, but have a lot more color, and tend to be a little more active in my opinion.

One more thing - putting your hands in the tank consistently and moving things around is more of problem then those crabs. And if you are really concerned about them stealing food from corals and whatnot, use a turkey baster or a low flow power head and blow your rocks causing a small kick up of whatever is on the rock. A few benefits of this is corals feeding off the critters you've just thrown into the current, and also, corraline algae will grow where the sediment that you blew off once was. So more desirable algae and an easy/cheap way to feed your corals. But please do not over do this. Don't blow off every rock and expect a feeding frenzy (I would advise blowing off most of your rock prior to a water change, though). More than likely you will cause the corals to recede and possibly affect the oxygen exchange in your fishes gills.

Anyway, I went off on a tangent there. Hope I answered something.