Coral Crabs - benefit for coral

Oxylebius

Oxylebius

Well-Known Member
Another great article on coral crabs!

Smithsonian Articles and Research
http://newsdesk.si.edu/releases/smi...-coral-s-best-defender-against-army-sea-stars
http://newsdesk.si.edu/photos/coral-guard-crabs-t-serenei
Coral reefs face a suite of perilous threats in today’s ocean. From overfishing and pollution to coastal development and climate change, fragile coral ecosystems are disappearing at unprecedented rates around the world. Despite this trend, some species of corals surrounding the island of Moorea in French Polynesia have a natural protector in their tropical environment: coral guard-crabs.

New research highlighting the role of diversity in the healthy functioning of coral reef ecosystems, showing that guard-crab species and size classes offer different kinds of effective protection against various threats to coral reefs.

More Articles
http://www.aquariumofpacific.org/onlinelearningcenter/species/coral_crab1
At one time coral crabs belonging to the genus Trapezia, Tetralia, and Domecia were thought to be ectoparasites, living off of the tissues of the coral. Then it was discovered that these little crabs actually protected the coral in which they lived from predators, such as the crown-of-thorns sea star (Acanthaster planci). When the sea star begins to climb over a branching coral, these little crabs move to intercept it, pinching the sea star’s tube feet. The pain forces the sea star to crawl away, defeated.

When coral crabs are removed from their host coral, the lower branches become covered with algae, sponges, and tunicates. It has been speculated that movements of the crabs lower down in the coral colony increase water circulation and prevent detritus from accumulating in and on the coral’s branches.

http://www.fishchannel.com/saltwater-aquariums/reefkeeping/coral-crabs.aspx
Trapezia and other commensal crabs found in the branches of stony corals offer definite benefits to the coral. The next time you are lucky enough to acquire a coral colony with one or more of these beneficial crabs present, please do not recoil in horror, but rather leave them in place and your coral will thank you.

Coral Commensal Crab ID Page
http://www.chucksaddiction.com/coral_crabs.html
EDIT: Updated link for the ID page here: http://chucksaddiction.thefishestate.net/coral_crabs.html


And one of my Coral Crabs!

 
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DianaKay

DianaKay

Princess Diana
RS STAFF
@Oxylebius How many coral crabs do you have in your tank?
And did you acquire it (or them) with a coral purchase or as a seperate purchase? Do you spot feed your coral crab?
What do they eat? :crab3:
Lots of crabby wonders & thoughts of adding one :crab4:
 
Oxylebius

Oxylebius

Well-Known Member
I have two coral crabs.

One coral crab came on a aquacultured acropora coral head. The only large coral I purchased as all of my other corals came as frags from other reefers tanks. I took a risk and didn't dip this coral b/c the coral crab was in it. In hind sight, I should have taken a tooth pick and ushered the crab temporarily out of the coral, so that I could dip the coral w/o the crab in it. Then re-introduce the crab to its coral home when the coral was in my tank. But, it worked out fine w/o dipping it. No unwanted hitchickers on the coral and it has a nice array of barnacles and a large bunch of red foraminiferans, Homotrema rubrum. If I had dipped, these would have probably not have made it.

The other one I purchased. Actually I had purchased two coral crabs and one didn't survive as I didn't have two large coral heads for them and they fought over the one large neon green Poci coral.

They are super tiny crabs and sometimes very hard to see inside the corals. Here is a molt, as you can see it is less than a inch in size.


Here is another pic of it checking out a new rainbow stylo that was added to the tank. I had come into the room late at night, long after lights had gone out and I find it happily checking out the new frag, which was on the sand bed.


The crab would have a very hard time living in this sized frag and would probably end up dieing after a time. It was back in its larger coral head by morning.
 
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Oxylebius

Oxylebius

Well-Known Member
I feed the crabs chucks of fish food once a week (or mysis). Otherwise, they get what they need from the coral. They are known to eat the mucus produced by the coral they live in. On rare occasions they may eat a polyp or two, but if the coral is large and healthy it won't hurt the coral. The coral can reproduce the polyp easily.

From one of the articles that I posted:
  • These crabs primarily feed on coral mucus which has high lipid content and on detritus trapped in the coral mucus. They use specialized feeding appendages on the tips of their claws to stimulate their host colonies to produce excess mucus.
  • Research has shown that corals contain large amounts of lipids in their tissues. In fact, 30 to 40 percent of a coral’s dry tissue mass is lipid. The majority of these lipids are passed from the symbiotic algae in the coral to the coral’s tissues, with the rest being manufactured by the coral from metabolites of the algae.
In studies of the ubiquitous Hawaiian branching stony coral Pocillopora damicornis, Dr. John Stimson of the University of Hawaii found that the presence of Trapezia sp. crabs actually stimulated the coral to produce fat bodies, which were clearly visible as small, whitish globs in the tentacles of the polyps. These were then fed upon by the crabs. How this occurs is not clear. They could be eating the tentacles directly, they could stimulate the polyp in some way to cause it to release the fat bodies, or the fat may be exuded in coral mucus. When the crabs are removed, the fat bodies get larger for about a week, but then grow smaller.

Dr. Stimson recently discovered that if the crabs are fed, they readily release ammonia, but if they are not fed, they don't. This raises the possibility that when corals feed their crabs lipids, the crabs become living fertilizers, moving amongst the branches, releasing nitrogen-rich ammonia to the resident zooxanthellae. This may explain why polyps in the lower branches retain high vitality rates despite being exposed to less light.
 
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Oxylebius

Oxylebius

Well-Known Member
Great!

Do you have large sps corals of the species: pocillopora, acropora, and stylophora?

I suggest that you have all these corals in your tank b/c you won't know what crabs they are going to send to you.

And the corals should be a good size, not a frag, but a well established coral head. These crabs seek shelter in the coral and the coral needs to be able to provide food for the crab w/o the crab causing harm to the coral.

The crabs are very selective about the species of corals they select for a host, coral crabs establish habitats on stony branching corals (SPS) in the genera Acropora, Pocillopora and Sylophora. Crabs belonging to the genus Trapezia live in Pocillipora and Stylophora corals, and Tetralia and Domecia live in Acropora.

Don't make the mistake I did where I ordered two crabs, but didn't have the proper coral species to house it. They both wanted the same coral head and fought over it until one was pushed out. The second tried to live among the branches of several monties that were growing into one another, but the monti couldn't sustain the crab and it died. That is why I am stressing making sure you have the various corals that these crabs naturally live in.

Now, if you have these corals and you order the crabs...you may already know this, but acclimate and release the crab into the coral you want it in. But, beware that it may choose a different coral or move around the various corals at first until it finds a home suitable for it. If it doesn't find a suitable home, the likelihood of it surviving is low.
 
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Snelly40

Snelly40

Well-Known Member
i appreciate it and yah my frags are not ready nor big enough yet but i like to put in email noticifactions so i get reminders about the numerous items i do want haha



Oxylebius said:
Great!

Do you have large sps corals of the species: pocillopora, acropora, and stylophora?

I suggest that you have all these corals in your tank b/c you won't know what crabs they are going to send to you.

And the corals should be a good size, not a frag, but a well established coral head. These crabs seek shelter in the coral and the coral needs to be able to provide food for the crab w/o the crab causing harm to the coral.

The crabs are very selective about the species of corals they select for a host, coral crabs establish habitats on stony branching corals (SPS) in the genera Acropora, Pocillopora and Sylophora. Crabs belonging to the genus Trapezia live in Pocillipora and Stylophora corals, and Tetralia and Domecia live in Acropora.

Don't make the mistake I did where I ordered two crabs, but didn't have the proper coral species to house it. They both wanted the same coral head and fought over it until one was pushed out. The second tried to live among the branches of several monties that were growing into one another, but the monti couldn't sustain the crab and it died. That is why I am stressing making sure you have the various corals that these crabs naturally live in.

Now, if you have these corals and you order the crabs...you may already know this, but acclimate and release the crab into the coral you want it in. But, beware that it may choose a different coral or move around the various corals at first until it finds a home suitable for it. If it doesn't find a suitable home, the likelihood of it surviving is low.
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