What type of coral forms massive boulder-like structures?

Brain coral forms massive, rounded, boulder-like colonies. Its winding ridges and valleys resemble the folds of a mammalian brain, giving the group its familiar common name.

“Brain coral” is a broad common name rather than one single species. Several colonial stony corals, including symmetrical brain coral and boulder brain coral, grow into domes or large hemispheres. Some colonies can reach roughly 2 meters across and may live for more than a century because their growth is slow.

The coral’s living polyps occupy small skeletal cups along the ridges and valleys. During daylight, they often retract; at night, they extend tentacles to capture zooplankton. Symbiotic microscopic algae called zooxanthellae provide additional energy through photosynthesis.

A common mix-up is confusing brain coral with staghorn or table coral. Those corals typically form branching or plate-like shapes, while brain corals are recognized by their solid, massive colonies and maze-like surface patterns.