Red-spotted Coral Crab

Geographical Origin and Habitat: Widely distributed throughout the tropical Indo-Pacific, from the Red Sea and East Africa to Hawaii, Polynesia, and the Galapagos. Found strictly within live colonies of branching corals (Pocillopora or Acropora).

Taxonomy: Member of the family Trapeziidae. Features a smooth, shiny trapezoidal carapace measuring about 3-4 cm in width. Legs have curved tips adapted for clinging tightly to coral branches. Grows to 3.5 cm.

Social Behavior: Mutualistic symbiont. Actively defends its host coral from predators (like the Crown-of-Thorns starfish, Acanthaster planci) by pinching their tube feet. Typically lives in stable male-female pairs.

Coloration and Sexual Dimorphism: Spectacular color pattern of a white, yellow, or pinkish-cream base body covered in large, regularly spaced bright red or reddish-orange spots. No visible sexual dimorphism.

Tank Setup: Must be kept in a mature reef tank of 20 gallons or larger containing at least one healthy colony of branching coral (Pocillopora or Acropora). Does not require empty shells.

Diet and Feeding: Feeds on coral mucus and organic detritus trapped between the coral polyps. In aquariums, it also catches suspended food like mysis or brine shrimp from the water column.

Water Quality: Reef parameters. Salinity SG 1.021-1.025, pH 8.1-8.4, temperature 22-28°C. Highly sensitive to copper treatments, elevated nitrates, and sudden salinity drops.

Compatibility and Tankmates: 100% reef-safe. Mutualistic protector of its host coral. Compatible with peaceful reef fish. Avoid predatory tankmates (e.g. hawkfish, wrasses, or groupers).

Aquarium Breeding: Microscopic larval stages are pelagic and complex, and do not survive standard home aquarium filtration systems.

Risks and Diseases: Direct dependence on the host coral; if the coral host dies, the crab will experience high stress and likely perish. Requires stable calcium and iodine for molting.