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Invertebrates: Crustaceans (Crabs)

Crabs are all opportunistic feeders, so care should be utilized in all cases.  If they are not fed adequately, they will find food in the form of snails, fish, etc.  Crabs grow by molting, so it is not uncommon to see what appears to be a dead crab in the aquarium with the real crab hiding to protect its soft new shell.

 

Staghorn Crab (Manucomplanus varians): Not Reef Safe
This neat crab has a symbiotic relationship with its shell.  The shell is composed of stinging creatures (similar to jellyfish) called hydroids and bryozoans.  The shell of hyroids/bryozoans protects the crab from predators.  When the crab eats, pieces of food remnants are often caught by the hydroids/bryozoans.  As the shell grows, the crab trims the opening with its claws.  Although this is a very unique crab, it is not recommended for most reef aquariums as the shell itself requires special care.  The organisms on the shell may die if the aquarium is not mature and stable enough.  Additionally, these stinging creatures may harm corals, or corals may harm it.  Lastly, due to the unique shape of the shell, the crab may not be able to right itself if it falls over.

Staghorn Crab (Manucomplanus varians)

Staghorn Crab (Manucomplanus varians)

Sally Lightfoot Crab (Percnon gibbesi):  Reef Safe with Caution
The Sally Lightfoot Crab is a scavenger and looks for detritus and dying matter to eat.  Its body shape allows it to fit into very tight places in the rocks and to run quickly to safety.  While the crab is great when smaller, as it grows it becomes more aggressive and may prey on small fish.  Keep in mind how hard this crab will be to catch as it grows if it becomes a problem.

Sally Lightfoot Crab (Percnon gibbesi)

Sally Lightfoot Crab (Percnon gibbesi)

Scarlet/Red Legged Crab (Paguristes cadenati):  Reef Safe
Red legged crabs are great scavengers by feeding on algaes, remaining fish food, and detritus.  However, if the food supply gets too low (or they like a snail’s shell better than theirs), then they will kill snails.  Because of this, keep enough food for the crabs (which is usually not a problem in most aquariums) and an available supply of various size/color shells.

Scarlet/Red Legged Crab (Paguristes cadenati)

Scarlet/Red Legged Crab (Paguristes cadenati)

Emerald Crab (Mithraculus sculptus):  Reef Safe with Caution
Like many crabs for the home aquarium, the emerald crab may become overly aggressive as it grows.  While small, the emerald crab is another great scavenger, and one of the few crabs known for eating bubble algae (Valonia) (some eat it more readily than others).  As a side note, the emerald crab will not eradicate bubble algae as its eating habits just release the spores into the aquarium for further propagation.  The emerald crab may also damage SPS corals as it becomes larger by literally taking out chunks to eat.  If you have a mature reef, you may not notice the damage, but if your tank is full of small coral fragments, the damage may be tremendous.

Emerald Crab (Mithraculus sculptus)

Emerald Crab (Mithraculus sculptus)

Green/Thin Striped Hermit Crab (Clibanarius vittatus):  Not Reef Safe
We named this little fellow, “Godzilla” for his tremendous strength and bulldozing capabilities.  These crabs are not reef safe since they grow quite large and will eat just about anything (including ripping one of my corals to shreds to eat the food it caught).  However, these are great scavengers for a non-reef tank without predators as they are able to survive a wide variety of temperature and salinity ranges.

Green/Thin Striped Hermit Crab (Clibanarius vittatus)

Green/Thin Striped Hermit Crab (Clibanarius vittatus)

Blue legged crab (Clibanarius tricolor):  Reef Safe
Out of all crabs available for a cleanup crew, these are the only ones I feel at all comfortable with.  They are great scavengers, and their small size allows them to maneuver throughout the aquarium rather well.  They eat algaes of many types, detritus, and leftover fish food.  Provide plenty of extra shells in various sizes and colors so the crabs will not kill snails for their shells.

Blue legged crab (Clibanarius tricolor)

Blue legged crab (Clibanarius tricolor)

Arrow Crab (Stenorhynchus seticornis):  Reef Safe with Caution
The arrow crab is quite unique, and is ok for a reef aquarium without small fish (arrow crabs are known to catch small fish).  They are also the mortal enemy of banded coral shrimp and should not be housed with one.

Arrow Crab (Stenorhynchus seticornis)

Arrow Crab (Stenorhynchus seticornis)

Arrow Crab Close Up

Arrow Crab Close Up

 

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  1. Invertebrates: Crustaceans (Crabs) Part II » Reef'd Up Aquatics

    […] See Crabs Part I here. […]

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