The Mithrax sculptus (Emerald crab) journal

[ragc]

Today I introduced one Emerald crab into my tank with the express purpose of making him/her happy by offering free bubble algae she/he can enjoy in abundance and free of charge. In investigating what could take care of my bubble (and green hair?) algae I ran into some that posted that Mithrax may not eat the stuff...

The literature, most specifically Ronald L. Shimek, Ph.D., in Marine Invertebrates , T.F.H. Publications/Microcosm Ltd., 2004 states this crab is "Truly an oddity among crabs" as it is mostly hervivorous. Dr. Shimek goes on to tell us that "This is one of the few aquarium animals that will eat bubble algae". Also some have reported that theirs does eat the nasty algae, confirming the data offered by Shimek.

Because I needed a crab (for aesthetic reasons) and have plenty of the green bubbly stuff I don't want, and some green hair algae I also would like to stop pulling by hand, I am taking the challenge up. I have introduced Mithrax sculptus into my 10 gallon SW/reef/planted setup and will post the results here for all to read.

Today, day 001, I present the existing state of my rock column, with abundant bubbles. Bubble algae also exists in other locations of my tank not seen in this photo. The second photo is of the crab (no name yet) as it was being acclimatized to my tank water. The third photo is the crab in his first hiding place, under the rock pillar, 3" away from a succulent bubble alga!

More to come...

 

[ragc]

End of day 001

Crab out of crevice after 20 min in tank, climbed 1", pulling at rock, especially in crevices, and eating. Saw him pull some coralline algae and eat it (not good). Climbed up to a bubble, touched it, then darted back to crevice.

Several hours later crab behind rock (see photo). Original "touched" bubble not there anymore (eaten?). All other bubbles seems to be there.

Lights out. Crab becomes active, walking to front of rock, where there is plenty coralline and green filamentous algaes (second photo), Morning will tell.

Question: My pencil urchin comes out at night to feed on detritus. Could they harm each other in the dark? My Yellowtail Blue Damsel is not happy at this intrusion...she will have a very bad night in her cave, especially if the crab comes a' calling! More tomorrow...

 

[Blinky]

I'm curious, is your crab a male or a female? I had bad luck with a male pink mithrax, it ended in a coral-eating free-for-all and a trip to the LFS and a nice FOWLR home for him. I've got a green female in my reef now and she's an absolute model citizen. I'm keeping a little male in my FOWLR (which may end up as a reef afterall) and doing my own experiment as to whether the sex of the crab has anything to do with developing an insatiable appetite and going after coral. I suspect my bad luck was more to do with the fact that the other crab wasn't an emerald, just very closely related, and nothing at all to do with the fact that he was male but it's interesting to keep track of others' male crabs just the same.

 

[ragc]

How can I tell if my crab's girl or boy?

Looking at the tank this AM it looks like the crab was very respectful of everything, but lights-on is hours away still, so no "official report" yet.

 

[Blinky]

See if you can get a look at its underside. Males have a point that divides their midsection in two, females have a much wider 'tail' and their midsection looks a little like a sixpack. With those big arms I'm guessing you've got a male, but you never know...

 

[ragc]

Day 002

I will turn the crab over as soon as I can reach him/her. At this moment it's on top of a large conch entangled in kelp that I keep on the 'lagoon' side of my tank as an alternate hiding place for Lil'B, my yellowtail damselfish if the pencil urchin takes her rock cave in the 'breakers' side of the aquarium. It cannot be reached. I have attached the best photo I can of the crab on the conch, taken through the gap between my surface skimmer and it's piping to the power filter it connects to.

The night went well, without destructive behavior. I noticed one bubble algae is gone, some of the tuft of hair algae on the cusp of my rock pillar is also gone. I saw it pull at hair algae yesterday, so if this is going to be it's habit I could not be more thankful! The attached photo of the pillar documents the difference today. The missing bubble alga was on the bottom, left in yesterday's photo. This is the same bubble it touched briefly before scampering (see day 001).

More to follow...

 

[ragc]

Caught! End of log... Day 002 (8:20 PM EST)

Well...we went back to the rock pillar and were caught munching on bubble algae...case closed! The Emerald crab (Mithrax sculptus) does eat bubble algae. See attached photos. :dance:

 

[kobeSumo]

That's great! I'm going to buy a algae attack pack at my LFS for getting rid of my brown algae, now that I have my RO unit.

 

[ragc]

It's a male.

 

[Coralline_Reef]

Fighting emeralds?

I just got an order of emerald crabs in & am acclimating them to my tank....
I have them together in a tupperware right now... and they seem to not get along. They are pinching and chasing each other.
Is this a problem? I don't want to put them in the tank and have them damage any corals or the cleaner shrimp & peppermint shrimp - or each other.
Are they completely reef safe??
Are they safe to put in together?? Should I put a male and female together or is same sex better?