What Divers Should Know About Stony Coral

Stony corals, or scleractinians, are the fundamental architects of many marine ecosystems, forming the hard framework of modern coral reefs found across all the world's oceans. These fascinating animals are individual polyps, marine creatures in the phylum Cnidaria, that meticulously secrete hard calcium carbonate skeletons. While some species are solitary, often growing up to 25 centimeters across, most are colonial, with their tiny individual polyps typically measuring just a few millimeters in diameter. These colonies can collectively reach impressive sizes, often several meters in height or diameter.

When you observe a vibrant shallow-water reef, much of the color you see comes from these stony corals. Many contain microscopic symbiotic algae called zooxanthellae within their tissues, which provide the coral's diverse hues depending on the specific symbiont species present. Keep an eye out for their delicate tentacles; these polyps possess stinging cells, similar to sea anemones, and can swiftly retract into their stony cups if disturbed, offering a brief glimpse into their living nature within the reef's structure.