By Charles & Linda Raabe
Mactan Island, The Philippines

© 2016  ALL RIGHTS RESERVED

  I have never found a crab yet that has hitchhiked into my tank that I would consider reef safe. The only crabs that I consider to be truly reef safe are the commensal types such as the porcelain crab and coral crabs. The only reason such crabs can be considered reef safe is that they never leave their hosting spot. The hermit crabs that are intentionally introduced to our tanks are not to be trusted or considered reef safe either, all crabs are omnivores and will eat what ever they can. While most corals are safe from hermit types, other inverts and fleshy polyp corals are not.

CRAB ARTICLES

    The Xanthidae Crabs  (link - extensive photo gallery)  None of which can be considered reef safe and can be the most destructive of the crab types. While very small, they seem to pick at algae on the rocks, but just as with other crabs species, once they gain a bit of size, their ability to pick off and eat any number of invertebrates and corals also increases. They also have a bad habit of enlarging their hiding places within live rock and will, in due time, weaken the rock considerably.
      Below, a commonly found Xanthid species living within live rock.
       
      Below, yet another rock living Xanthid species.
       
    Below is a Xanthid species found on Acropora corals and assume they prey upon the corals polyps or tissue.
       
      Various other Xanthid species.
      
     


      The  Hermit Crabs     Hermit ID site          Paguritta Hermit Crab    
     


      The  Mithrax Crabs  ( Cling Crabs)   None of which I would consider to be reef safe, members of this family include the popular "emerald" crabs that are used for algae control, which may be fine for awhile, but with all crabs being omnivores, it is usually only a matter of time before these crabs discover that there are meatier items to be had within your aquarium.
      
      
       
      


    The Porcellanidae Crabs   Photo Link #2   Photo Link #3   Can be considered Reef Aquarium Safe
      
      
      
     The Anomuran crabs, part of the Porcellanidae family, relatives of Petrolisthes and Porcellanella.
       
       Petrolisthes species
    


      The Galatheid Crabs - Also known as squat lobsters for their appearing very lobster like. All of the species that I have found on live rock have been very small and seem to be somewhat harmless, although they may feed upon small sessile invertebrates.
       
       
      

      The Allogalatheid Crabs -  also known as squat lobsters but only lives on crinoids. Color patterns usually consists of alternating dark & light colored bands with white leg tips & claws; the colors always match the host crinoid. They are klepto-parasites that don't directly harm the host but steal its food.
               Allogalathea elegans
       




     The Dromiidae Crabs - Specializes in carrying sponges and even zoanthids as a means of camouflage, it does so by means of its last set of legs which are modified to grasp onto its captive audience. I have had this specimen drop its sponge and snip out a square inch section of zoanthids off of their rock and form the zoanthids into the same shape as the sponge pictured below. I have seen others on the reef slopes carrying about both sponges and zoanthids in this manner.
      
      


      The Portunidae ( Swimming Crabs) Note the paddle shaped last pair of legs.
       

       
    Below:  A Lissocarcinus laevis, a symbiont of sea anemone.
       
     Below:  Various other species
     


      The Majoidea SuperFamily  ( spider crabs / decorator crabs)
       
      Below:  Xenocarcinus tuberculatus   A member of the Pisidae family
       

           Below:   Achaeus japonicus
         

      Below: Various other unknown species
       
       


      The Parthenopidae Family, commonly called the elbow crabs. Below is a possible Daldorfia horrida.
       
       Below, possibly a juvenile Daldorfia glasselli.
       


      The Calappa Crabs  ( box crabs )    
                    Gravid Female                                                  Ready to hatch eggs                                            Two day old Larvae
      


      The Leucosiidae Crabs  ( Pebble Crabs)
            Below, a member of the Leucosia genus
         


       The Cryptochirid Crabs  ( Gall Crabs )
       

        The Pinnotheridae Crabs  ( Pea Crabs)  -  Pea crabs are commensals that associate with various echinoderms, molluscs, polychaetes, brachiopods, etc.  Some are external while many of them are internal living inside their hosts' gill chambers or body cavities.  (photos by Beth LeBlanc)
     
   
         
      The Stenorhynchus Crabs  ( arrow crabs )  Normally not considered reef aquarium safe
     
 

  It is our hope that by documenting the coral and crab species found as commensals we can help to determine which crab species should be targeted for breeding efforts. If we are to ever transplant any of the branching corals out onto the reefs as a restoration project, we will have to include a variety of coral crab species as well.

                                                             Click Links to view photographic details

                   Specimen #1                                        Specimen #2                                          Specimen #3                  Jonesius triunguiculatus                         Tetralia cinctipes                                  Trapezia septata    

 
Cymo andreossyi : Very common and is considered a coral symbiont, with the caveat that such symbiosis are a trade off between the coral and the crab, the coral gains protection and house cleaning services while giving up a few polyps, mucus and captured/settled food particles in exhange for those services.  A healthy coral should have no problem repairing or replacing lost polyps, but again, in an aquarium environment, an eye should be kept on the coral for excessive damage being done due to the coral being unable to recover as fast or faster than the damage being done by the crab.  In short, its a judgement call that you will have to make.




    Four New Species of Coral Crabs Discovered
    Trapeziid Crabs of New Caledonia, Eastern Australia and the Coral Sea