Hydroids Growing on Emerald Crab

[Fossilized Reef Mode]

I have had this crab for over a month and didn't see him for a couple of weeks. The other day he made an appearance sporting a wardrobe of hydroids. I have since noticed little colonies of these hydroids in three or four other spots. Should I be concerned?

Tank is a 3.5 month old 36 gal bowfront
Nitrate - 7.2
PO4 - 0.05
Sal - 1.025

cuc
5 blue legs
2 trochus snails
Feather duster worm
Copepods

Fish
Black Clown
2 firefish
Yellow clown goby

Coral
Zoa
Toadstool mushroom
Mushroom

 

[Jay Hemdal]

I have had this crab for over a month and didn't see him for a couple of weeks. The other day he made an appearance sporting a wardrobe of hydroids. I have since noticed little colonies of these hydroids in three or four other spots. Should I be concerned?

Tank is a 3.5 month old 36 gal bowfront
Nitrate - 7.2
PO4 - 0.05
Sal - 1.025

cuc
5 blue legs
2 trochus snails
Feather duster worm
Copepods

Fish
Black Clown
2 firefish
Yellow clown goby

Coral
Zoa
Toadstool mushroom
Mushroom

Welcome to Reef2Reef!

I've never seen that on emerald crabs, but I have seen it on giant Japanese spider crabs. In those, it had something to do with how infrequently they molted.

With regular crabs, they reach something called "terminal molt" where they don't molt again. That allows all sorts of other things to grow on their shells - algae, hydroids, sponges, etc.

I don't think there is any way you could treat this without also harming the crab.