Denuded areas under acro branches…why?

[Ancient Mariner]

I have a 2.5 year old ORA Carl acro that’s doing great. However there are a few branches that have denuded areas on the underside. This started developing about 4-5 months ago, coincidentally soon after introducing a citron goby. I do see the goby rubbing it’s belly along the undersides of the branches of multiple acro colonies but this acro is the only one with damage.

Anyone else have this issue with healthy acropora colonies? Is it the goby?

 

[Jekyl]

Shading?

 

[Ancient Mariner]

Shading?

I don’t think so since there are plenty of other branches that are in deeper shade without damage.

 

[dennis romano]

I believe the reason is in your second picture. Citron gobies nip at acro polyps.

 

[Ancient Mariner]

I believe the reason is in your second picture. Citron gobies nip at acro polyps.

That’s my suspicion. It isn’t nipping, but rubbing. But no other acro colonies are affected and I do see the goby rubbing against them as well.

 

[rgulrich]

I ran across these guys a number of years ago, and switched over to other of their "cousins" as an alternative.

The page you'll be looking for is 17/19 (marked as 89 in the paper).
Impact of coral predators on tropical reefs; Randi D. Rotjan, Sara M. Lewis

https://www.int-res.com/articles/meps2008/367/m367p073.pdf

Gobiodon citrinus Consumption rate and coral prey columns.
Other research will also tell you they produce a toxic mucous.
Cheers,
Ray

 

[Ancient Mariner]

I ran across these guys a number of years ago, and switched over to other of their "cousins" as an alternative.

The page you'll be looking for is 17/19 (marked as 89 in the paper).
Impact of coral predators on tropical reefs; Randi D. Rotjan, Sara M. Lewis

https://www.int-res.com/articles/meps2008/367/m367p073.pdf

Gobiodon citrinus Consumption rate and coral prey columns.
Other research will also tell you they produce a toxic mucous.
Cheers,
Ray

Perfect! Great paper. Interesting that they list it as an obligate corallivore. Mine eats mysis very aggressively! But seems to be very picky about the coral in my system!

 

[rgulrich]

Highly refined tastes, I believe. Mine only went for the more expensive acropora. Probably wouldn't be a problem if added to a system with a robust acropora population and rapid growth rate.
Cheers,
Ray

 

[Ancient Mariner]

90% healed up with no new recurrence. Citron goby is still present. I don’t think the damage is from the goby eating the coral. I suspect it caused the damage as nest preparation. I do see it rubbing its ventral aspect along the coral branch, much as a clownfish rubs against the glass in preparation for spawning. As no further denuding has occurred this may only happen seasonally or when the goby is in breeding condition. We’ll see if this happens again.