Mystery Crab

[SaltwaterNoobs]

Found yet another hitchhiker on our new piece of rock (4th one found 3 days after purchase). Not so sure what this guy is, though. He's a small crab that likes to hide inside the rock during the day and come out at night (caught him last night when I turned the moonlight on to check for nudibranches and he was on top of the new zoanthid rock. He looks to be white with red spots on him. Every picture I've seen of this type of crab suggests he's a porcelain, but I thought porcelain's ate using their fan-type claws, not digging at stuff on the rock. I'd post a picture, but he's really fast to hide once that light comes on. I've heard and read that most crabs (other than hermit and maybe emerald) are generally not a good idea in the tank because they will eat corals and zoanthids, etc. If this is the case, should I try to get this guy out of the tank? I have a puffer that would find him to be a delicious snack, I'm sure. Any and all advice/information would be appreciated!

 

[ashton]

i'd say its better to be safe then sorry. IF it doesnt have the fan like claws then its not a porcelain crab.

 

[bigblue141]

I would pull the rock, dip it in fresh water, let the critters scurry out of the rock, then toss them in your sump.

Crabs eat lots of stuff, just happens a lot of stuff we don't want them to eat are kept in our DT's.

 

[SaltwaterNoobs]

I would pull the rock, dip it in fresh water, let the critters scurry out of the rock, then toss them in your sump.

Crabs eat lots of stuff, just happens a lot of stuff we don't want them to eat are kept in our DT's.

But will the freshwater dip harm the zoanthids on the rock? There are two green poly's also growing on it.

 

[mfinn]

I would not trust any crab that came in on live rock. I have lost way too many zoanthids to preditor crabs.
I would take a small wide mouth jar, such as a small baby food jar, weigh down a piece of raw shrimp with a small piece of live rock. Put the jar in the tank at the base of the rock work where the crab might be. Tip the jar so that it leans against the rock at about a 45 degree angle. The crab can get in but can't get out.
It may take several nights, but eventually he should get trapped.

 

[SaltwaterNoobs]

I would not trust any crab that came in on live rock. I have lost way too many zoanthids to preditor crabs.
I would take a small wide mouth jar, such as a small baby food jar, weigh down a piece of raw shrimp with a small piece of live rock. Put the jar in the tank at the base of the rock work where the crab might be. Tip the jar so that it leans against the rock at about a 45 degree angle. The crab can get in but can't get out.
It may take several nights, but eventually he should get trapped.

I'd thought about doing a trap like this, but I have hermit crabs (of all sizes) in the tank as well, and I don't want one of them getting to the bait before the other crab. Would a freshwater dip harm the zoas on the rock if I chose that route?

 

[mfinn]

I'd thought about doing a trap like this, but I have hermit crabs (of all sizes) in the tank as well, and I don't want one of them getting to the bait before the other crab. Would a freshwater dip harm the zoas on the rock if I chose that route?

Oh I can guarantee that you will catch a few hermits in the process. But it doesn't hurt them. Just pick them out and rebait.

Depending on how big the rock is, do you want to kill the bacteria on the rock waiting for the crab to come out. He may get stubbon and hold his breath, or gills....
Crabs can survive a long time without being in saltwater,,,, days.

I've dipped zoanthids in freshwater many times, but only a few minutes at a time.

I read a story on RC about a guy who knew exactly what hole a certain crab was in. He couldn't reach him it was in so deep in the rock. So he took the rock out of the tank and filled the hole the crab was in with selzer water.
I guess the crab came right out.

 

[SaltwaterNoobs]

Oh I can guarantee that you will catch a few hermits in the process. But it doesn't hurt them. Just pick them out and rebait.

Depending on how big the rock is, do you want to kill the bacteria on the rock waiting for the crab to come out. He may get stubbon and hold his breath, or gills....
Crabs can survive a long time without being in saltwater,,,, days.

I've dipped zoanthids in freshwater many times, but only a few minutes at a time.

I read a story on RC about a guy who knew exactly what hole a certain crab was in. He couldn't reach him it was in so deep in the rock. So he took the rock out of the tank and filled the hole the crab was in with selzer water.
I guess the crab came right out.

That could work! We know which hole he lurks in, so maybe we will try to selzer water. Otherwise bait it is! Thanks for the advice!

 

[jrgilles]

I've dipped zoanthids in freshwater also with no harm done. Many times, but just for a few minutes.