The Acropora Crab, Trapezia sp., is a commensal crustacean living amongst the branches of (primarily) Acropora corals. This great little crab, maintains a symbiotic relationship with it’s host coral by keeping its branches clean while feeding on small particles trapped by the coral polyps. While several hobbyists consider the Acro Crab a “pest” (some claim that it discourages polyp extension), it is now believed that it may increase success with keeping SPS by keeping the coral clean, and fending off any invaders or predators. We regularly see these obligatory commensal crab picking small pieces of mysis shrimp off of the various host Acropora species.

As with most invertebrates, the Acropora Crab will not tolerate high nitrate levels, or any copper-based medications.

Photo by Felicia McCaulley