Nature's Exterior Decorators
The common name “Decorator Crab” can be applied to many different animals, several of which are in different genus, and this has caused some miscommunication over the years. All Decorators share a specific trait, in that they all cover themselves with stuff. Sometimes this stuff consists of debris common to their environment, and serves as camouflage to hide them from predators, sometimes they will cover themselves with small stinging anemones or other distasteful prey items (also in an effort to deter predators). Some species of these crabs will also use their “stickyness” to hoard food items for later consumption. Some species of Decorator Crabs will molt their carapace (shell) and then pull their old decorations off and affix them to their new carapace!
For years, it was thought that Decorator Crabs would spit out a type of glue and use it to affix things to their shells. More recent research has shown us that the crabs are actually covered in a natural velcro, and that they prep items for sticking to this natural velcro by “chewing on an edge” of whatever will be attached. Under a microscope, it is hard to differentiate the appearance of velcro hooks and the shell of a decorator crab!
Several species of Decorators get very large, and as they get larger, stop decorating themselves intentionally (though through contact and algae growth, will still sometimes get adorned with differing things.) As such, the most popular choice, and likely most appropriate size wise Decorator Crab for the home aquarium is Camposcia retusa. These crabs are generally called “Decorator Crabs”, but are also sometimes called “Velcro Crabs” and “Camposcia Crabs”. Occasionally (and very incorrectly) they are called “Harlequin Crabs”.
Camposcia retusa is a pretty small crab, growing only to about 4 inches wide (including the legs) and with a shell that gets barely over an inch wide. They are found from the coast of Africa in the Indian Ocean to some islands in the Central Pacific, though most of the crabs we see as aquarium keepers come from the East Indian Ocean. They can be found in a huge variety of environments like sea grass beds, coral reefs, rubble zones, lagoons and even tide pools. From water over 200 feet deep, to pools that get landlocked by receding tides, they can be found at a huge variety of depths as well. Most of the crabs collected come from shallower environments, which makes them well adapted to swings in water temperature and even quality.
Keeping Camposcia retusa is easy. A natural omnivore, they take prepared aquarium foods without fuss; here we feed them a mix of sinking pellets and thawed marine meaty foods. In the home aquarium, they will also consume detritus. Hobbyists should not count on detritus as their sole food source, as they will need more nutrition and calories that will be available from natural waste. As previously referenced are not picky when it comes to water quality or temperature. There is some difference of opinion when it comes to the topic of appropriateness for reef tanks. While this species of Decorator Crab is unlikely to consume most corals, they will attempt to cover themselves with whatever they find, which could mean your corals, especially polyp corals. There are pictures of them covered in Zoanthids and Palythoa, and we've had a few of those in stock over the years. Larger tanks more densely covered in coral growth are obviously more likely to be able to absorb the damage caused by the crabs camouflaging themselves. Underfed crabs are also more likely to menace soft corals and clams. Whether or not you want to attempt to keep them in your mini-reef is up to you. The only other word of caution we would have is to avoid keeping them with large predators like Pufferfish or Triggers that would easily make a snack of them.
If you are interested in keeping a very different clean up crew member than the ones you usually see, Decorator Crabs (Camposcia retusa) should be on your list for sure. In small aquariums, this hardy crab is so unique it could be considered less of a cleaner, and more of a feature! Ask your LFS about getting you one from Quality Marine today!