Acro Crabs

[DrHank]

Rather than hijack someone else's thread I figured I'd start a new one. I'm sure that most of us have heard the debate about keeping versus getting rid of Acro crabs. Many keep them because they feel that these crabs are not harmful. I would like to know in what way, if any, are these crabs beneficial to the coral.

[Frankie]

I have a few in my reef. I am not sold that they benefit the coral yet. I do see them cleaning up the fish food particles that get stuck in the coral but i am also wondering if there rubbing off the tissue in areas on my acro's. I hope someone with more experience chimes in on this thread. Maybe Cheeks?

[mps9506]

I think there is still a lot not know about this relationship yet. But here some links:
Tiny crab protects coral
IngentaConnect Symbiotic crabs maintain coral health by clearing sediments

From the second link

In a field experiment, mortality rates of two species of branching corals were significantly lowered by the presence of crabs. All outplanted corals with crabs survived whereas 45-80% of corals without crabs died within a month. For surviving corals that lacked crabs, growth was slower and tissue bleaching and sediment load were higher. Laboratory experiments revealed that corals with crabs shed substantially more of the sediments deposited on coral surfaces, but also that crabs were most effective at removing grain sizes that were most damaging to coral tissues. The mechanism underlying this symbiotic relationship has not been recognized previously, and its role in maintaining coral health is likely to become even more critical as reefs worldwide experience increasing sedimentation.

A little something to chew on

[mps9506]

Originally Posted by FFrankie

I have a few in my reef. I am not sold that they benefit the coral yet. I do see them cleaning up the fish food particles that get stuck in the coral but i am also wondering if there rubbing off the tissue in areas on my acro's. I hope someone with more experience chimes in on this thread. Maybe Cheeks?

There is some folks that say that the crabs may munch or pull off some of the coral mucus. Personally I find them too small to observe that type of behavior in my tanks. One thing I know they don't do is prevent red bugs...

[Frankie]

Don't say the red word! LOL. Thanks for the info mike. Hey the surf is up here!

[mps9506]

Yea I know. I'm landlocked this weekend.

[DrHank]

Thanks Mike you've answered my question. I hope a bunch more folks are curious and read your references.

[mps9506]

I'm hoping most people leave the crabs in their acros. I do know I tried to remove a crab one time at the request of a customer. I think I did more damage to the acro than the crab could have ever done. Those guys are not easy to get out. Unless they see another coral they like better.

[BrothaWolf]

Thanks Mike! The trapeziid crab in your first link looks exactly like the one in my purple monster.

[michael_cb_125]

Here is an interesting link:
Image Quest 3-D Articles - Symbiosis on the Reef

[mps9506]

From the link Michael posted:

This defence is so effective that, if given a choice, COTS will actively avoid feeding on Pocillopora damicornis in favour of specimens of Acropora which have less aggressive crustacean symbionts. Only when there is little alternative will the starfish resort to feeding on P. damicornis colonies. Indeed, where P. damicornis is abundant, it may form natural barriers to COTS and create predation refuges for other species of corals, thereby helping to maintain coral biodiversity on COTS affected reefs.

That is very interesting. The crown of thorn star has become a serious problem in some areas where overfishing has occurred. It never occurred to me that a small crab like that could actually ward of one of those stars.
Silly acro crabs need to step up there aggression to protect their homes

[Dentoid]

Crabs are evil? Huh! The "Crabs Are Evil Society" is going to lose some members after this breaking news!

[Frankie]

Originally Posted by Dentoid

Crabs are evil? Huh! The "Crabs Are Evil Society" is going to lose some members after this breaking news!

Notice i never joined. I still hate the look of them though! I do have an emerald crab in my refugium. Came in as a hitcher.

[Dentoid]

Frankie, I was so impressed wsith your Sun corals that I ordered one from Extreme Corals. It's due to arrive on Friday! I swore I would never get one due to its feeding requirements, but I broke down because they are so beautiful. I hope it doesn't come with crabs!

[mps9506]

I've always liked crabs, just not the ones I learned about in my sex ed class in high school