Hermit Crab Mortalities

My recently acclimated hermit crabs have been dying off under suspicious circumstances. Usually I find the crab, dead and out of its shell with the soft abdomen eaten away. I was assuming they were dying from an undetectable water quality issue and then being scavenged, but I hve noted that most of the empty shells are either broken or have a single hole, about 1/8 to 3/16 in. in diameter, bored through the shell about the same distance above the opening, as though the crab was attacked, pulled into its shell, and then something bored through the shell to get at it.

The denizens of my tank are:

Brittle Star
Serpent Star
Coral Banded Shrimp
Peppermint Shrimp, 3
Fighting Conch
Astrea Snails
Nassarius Snails
Cerith Snails
Emerald Mythrix Crabs, 2

Down to about 10 hermit crabs, mostly the larger ones and mostly only the Blue Legged crabs remain out of about 15 Blue Legged and 15 Scarlet.

Everything except the stars and the Coral Banded Shrimp are quite small. I have watched all three under my new moonlight and they appear peaceful. Any ideas what the culprit might be?

 

I have never seen a mantis bore a hole before. They will crack shells but I've not seen any holes.

I'm a little curious myself. A mantis would typically go after the snails as well as the hermits but you don't mention any snail losses.

Are they dieing all over the tank or do the deaths seem localized to one small area?

 

All over, but mostly on top of the rocks and in the center of the tank, between my two live rock "crests". I do not believe I have any Mantis Shrimp.

 

Does the hole in the shell look like it has been smashed in or is it a smooth shape?

John

 

They look somewhat smooth and pretty circular, looking more drilled than smashed.

 

Hmmmm sometimes shells have natural holes ( vents ) in them and I was wondering if this is what you are seeing.

Are you sure that the hermits are not just moulting. The moult can be very deceptive as it looks just like a whole body.

I remember it happening to me, finding what I thought was a body and an empty shell. I examined what I though was the body and it looked a mess, like the stomach had been eaten out. I put what I thought was the empty shell on the tank cover glass, went away for a few minutes, came back to see the crab ( and shell ) scooting along the glass and finally diving back into the water

John

 

Yes, I'm certain. Shells that were whole the day before are violently penetrated. Some have the last, largest spiral cracked off completely, but most have a neat hole "drilled" into them. Seems unlikely to be cause by molting. I might have believed one or two to be caused by falling off rocks, but 10+? Not likely. No more fatalities today, so far.

 

I have no idea then.

Maybe it was one of these evil critters

Urosalpinx cinerea

Quote " The Atlantic oyster drill does not exclude other forms of shellfish from its diet. It often consumes other bivalves, gastropods and crabs. "

Quote " Urosalpinx cinerea uses both a secreted chemical to soften the shell of its prey and deploys its radula, or long, toothed structure that extends from its mouth like a file, to drill a hole in the tough oyster shell. It then inserts its proboscis into the hole and feeds on the soft meat of the oyster. Although it seems to prefer juvenile oysters, the snail also drills through the shells of mussels, barnacles, and other tough-shelled aquatic animals that inhabit the reefs. "

http://www.chesapeakebay.net/info/atlanticoysterdrill.cfm

Cheers

John

 

Wow That is pretty cool John I never herd of them before I was thinking this was one for Mulder & Scully on the X Files ;D

All Kidding aside Have you ever herd of anyone getting one of these Evil creatures in there Reef Tank? :-/

 

No, I haven't heard of one in an aquarium and if it is the culprit it would be a million to one chance

Either way it's better than finding Gillian Anderson in ya tank Or is it?

John