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 Verified Community Expert]

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.

 

[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

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.

Thank you for the response. I yoinked the crab from the dt and was going to wait for it to molt but I dont think he is going back. Especially if it has already reached terminal moltage (good name for a movie). I was able to also pull the small rocks and treat the hydroid patches. Hopefully I managed to get ahead of any potential issues or infestation.

 

[Jay Hemdal Verified Community Expert]

Thank you for the response. I yoinked the crab from the dt and was going to wait for it to molt but I dont think he is going back. Especially if it has already reached terminal moltage (good name for a movie). I was able to also pull the small rocks and treat the hydroid patches. Hopefully I managed to get ahead of any potential issues or infestation.

Oh, I misunderstood - I didn't realize that you were concerned about the hydroids in general, I thought you were just concerned about them growing on the crab.

The tank looks fairly new - tanks often go through a "boom or bust" cycle where one species of organism flourishes for some time, to then be replaced by something else.

I doubt that you will be able to physically remove all the hydroids, they will likely spread, but then their population will drop on its own, they really shouldn't cause any other issues.

Excess feeding, especially of liquid foods, will fuel their growth.