Polkdot Acro Crab
The Trapezia Pocillopora/Acropora Crab, or Acro Crab for short, is a small commensal crustacean which lives its whole life within the branches of Pocillopora corals and Acropora Corals if no Pocilloporid corals are available, aiding in the proper water flow between the branches to keep these areas clean. In a symbiotic relationship with its host coral, the Trapezia Pocillopora/Acropora Crab is thought to feed on particulates trapped by the coral polyps, fallen detritus, and the coral's secreted mucus. In turn, the crabs guard the coral from invaders and fend off predators.
The importance of the Trapezia Pocillopora/Acropora Crab's role within a larger reef ecosystem is just now being recognized. Previously considered by hobbyists to be a coral "pest," the Trapezia Pocillopora/Acropora Crab may actually improve your success with SPS husbandry. Since the crabs constantly clean and defend their hosts, corals hosting Trapezia sp. have higher survival rates and stronger growth.
In the home aquarium, they may eat excess meaty food particles that lands on the coral, but won't need to be provided a staple diet. As an obligatory commensal coral crab, though, they will require a host for survival.
Like other invertebrates, the Trapezia Pocillopora/Acropora Crab cannot tolerate high nitrate levels or copper-based medications.