Acropora millepora

Acropora millepora is a branching stony coral that forms small, clumped colonies with short, cylindrical branches. Its radial corallites are uniform in size and feature projecting lower rims, which give them a scale-like texture. The coral’s color varies widely, appearing as green with orange-tipped branches, pale pink, orange, plain green, or blue. First described in 1834 by Christian Gottfried Ehrenberg under the name Heteropora millepora, this species is native to the western Indo-Pacific, occurring in shallow waters from the east coast of Africa to Japan and Australia.

It is common across its range, which extends from the Red Sea, Kenya, and South Africa to India, Malaysia, Japan, Indonesia, and Australia, typically growing between two and twelve meters deep on reef flats, upper reef slopes, and in lagoons. Ecologically, Acropora millepora is zooxanthellate, hosting symbiotic dinoflagellates in its tissues. Its larvae prefer to settle on vertical surfaces and encrusting coralline algae, though at lower temperatures (22.5 °C) they become less selective about settlement sites and show reduced survival rates.

The local strain of symbiont—even before infecting the larvae—can influence their choice of substrate. The main threat to this species is the destruction of its reef habitat. As a shallow-water coral, it is vulnerable to bleaching and disease, and it is also collected for the aquarium trade. Rising sea temperatures and ocean acidification pose additional risks to corals generally, leading the IUCN to list Acropora millepora as "Near Threatened."