Mysterious disappearance of scarlet & hermit crabs

[unimike]

Hello, it have been long time since I have been here I am really stumped with the mystery of the disappearance of my crabs where I had about 25 crab mixed of scarlet and common hermit crabs where I have lost about 15 of them in past a month that I have discovered there are about 10 empty shells sitting in the back corner of the tank right behind the LR while there are 5 empty shell sitting on the other side of back corner of the tank behind the LR as well..there are enough room for the crab to crawl through from the side to back of the tank but I don't know what happening ? I do feed my creatures regularly 2 or 3 times per day. The creatures I have are:


Inverts:
-1 Skunk Cleaner Shrimp
-3 Nassarius Snails
-5 mixture of hermit and scarlet crabs

Fishes:
-1 Lawnmower Blenny
-1 False Perc Clownfish
-1 Clarkii Clownfish
-2 Spotted Cardinal fishes
-4 Blue Reef Chormis fishes
-1 Blue Tang

Corals:
-1 LR full of brown mushrooms (Assorted mushrooms)
-1 Medusa Soft Coral (Sphaerella species)

I have lost:
-2 Nassarius Snails
-4 Orange Cat Eye Snails

The water parameters are:

pH 8.2
Temp ~78 at morning and tops off at ~80 by tank lights out at night
Ammonia 0
Nitrite 0
Nitrate 10

I was told by LFS that something in the tank must be eating them but I have been monitoring much more closely in the tanks activity and I can't seem locate anything ? Help ?

Thanks in advance!
Mike

 

[Rays]

Possibly a mantis shrimp. Do you ever hear any clicking coming from the tank, especially at night?

 

[DrBDC]

Do you see broken snail shells anywhere? That would be a clue that a mantis is in there. Usually they just kill snails and take thier shells. IMO the tank is much better w/o the crabs but you need to find out what's up anyway.

 

[650-IS350]

clicks sometimes dosn't necessarly mean mantis.. could also be pistol shrimps... pistols you just hear clicks just like the mantis but you will hardly see them if ever unless they have a symbiotic fish they hang with... a mantis once aclimated and comfortable in your tank, you will start to see him roam around...

Try to wait till night time after the lights go off ( 1hr ) then use a flashlight with red light ( or use red film to cover the light spectrum ) most fish and inverts have a hard time seeing red light, but you can see em'

 

[unimike]

The problem is that...I won't be able to hear the clicks since I am deaf. (no apologizes needed please!) I will take a look at it at night when I have a chance...thanks.

 

[unimike]

<a href=showthread.php?s=&postid=9397320#post9397320 target=_blank>Originally posted</a> by DrBDC
Do you see broken snail shells anywhere? That would be a clue that a mantis is in there. Usually they just kill snails and take thier shells. IMO the tank is much better w/o the crabs but you need to find out what's up anyway.

No there's no broken shells...its just bunch of abandoned shells.

 

[fat-tony]

Are there any "alpha" hermits (larger ones)? They may be trying to get bigger shells by wiping out competition.

 

[unimike]

<a href=showthread.php?s=&postid=9402939#post9402939 target=_blank>Originally posted</a> by fat-tony
Are there any "alpha" hermits (larger ones)? They may be trying to get bigger shells by wiping out competition.

No...sadly from what I have collected from the "head counts" all of my known alpha hermits have been disappeared so those 5 crabs are small like the size of 1/4 to 1/2 inches.

 

[650-IS350]

I dont know if a large 1 1/2" pistol might kill them if there that small???

Yeah, try the lights out and use a flash light with a redlight..
I got the LED's with clip on RED or BLUE lense from OSH...
Target sells them too,

wait a while after lights are off.. make em comfortable to go outside

 

[unimike]

I guess I will go out and buy the "red light" flashlight soon...thanks!

 

[bj32482]

how is your algae, could starvation be a factor

 

[crabbejoe]

Put plastic wrap over the end of a flashlight with a rubberband and color it with a red magic marker. It works.

 

[AquaReeferMan]

If you dont see any damage on the shells it is not a pistol or a mantis. I have both of them. The pistol rarely does anything to any hermit or snail. If it does it will usually hit the shell a couple of times. To my knowledge it has never killed anything. My mantis on the other hand will basically break a shell in half. Im thinking more along the lines of a crab. They will just rip them out of their shell. You best bet is to look at the tank while its dark. That usually when I find everything bad.

 

[unimike]

<a href=showthread.php?s=&postid=9412614#post9412614 target=_blank>Originally posted</a> by bj32482
how is your algae, could starvation be a factor

algae have been gotten under the control however all of LR's surfaces is 90% covered with the green hair algaes which is constantly being trimmed by either tang or the blenny I haven't caught any of them consuming it but it does appear completely different from the time when the tank was completely covered with the hair alage now its just on the LRs.

I occassionally overfeed my tank so my crabs could eat the unfed foods...so its still a factor ?

 

[unimike]

<a href=showthread.php?s=&postid=9412815#post9412815 target=_blank>Originally posted</a> by AquaReeferMan
If you dont see any damage on the shells it is not a pistol or a mantis. I have both of them. The pistol rarely does anything to any hermit or snail. If it does it will usually hit the shell a couple of times. To my knowledge it has never killed anything. My mantis on the other hand will basically break a shell in half. Im thinking more along the lines of a crab. They will just rip them out of their shell. You best bet is to look at the tank while its dark. That usually when I find everything bad.

so its either the stravation or the other crabs trying to wipe out the competitons ?

 

[650-IS350]

My guess is you might have a hitchhicker rouge crab ( could be a large enough Gorrilla/Red/Rock crab.... caugt one large one dragging a snail to its layer... I could save the snail as I could not reach inside the cave..

You can also do a tilted bottle beside the rocks ( where you know the crab hides ) trick..... the crab smell food in bottle, tries to climb in to get food but can't climb out since bottle is smooth.. caught a couple that way... besides spear fishing them at night ( one of my favorite past times in reefkeeping )

=)

cheers