Question

What are reef producing coral called? What is the coral reef composed of? How are they created?

Answer 1

Short answers first, then a brief explanation.

1) What are reef-producing corals called?
- Reef-producing corals are called hermatypic corals (reef‑building corals). Most are stony corals in the order Scleractinia.

2) What is the coral reef composed of?
- Mostly calcium carbonate (CaCO3) in the form of aragonite produced as hard skeletons by stony corals.
- The reef framework also includes cementing coralline red algae, shells and skeletons of other animals (mollusks, foraminifera, bryozoans), sand and rubble, and a thin living veneer of corals, algae and other organisms.

3) How are they created?
- Coral larvae (planulae) settle on a hard substrate and metamorphose into polyps. Each polyp secretes a calcium‑carbonate skeleton; polyps reproduce asexually to form colonies.
- Many reef‑building corals host symbiotic algae (zooxanthellae, family Symbiodiniaceae) that photosynthesize, supplying energy and enhancing calcification—this lets reefs grow fast in warm, clear, shallow water.
- Over generations, living corals build atop the dead skeletons and are cemented by coralline algae and other deposits. If growth (accretion) outpaces erosion and sea‑level changes, a large reef structure forms (fringing reef, barrier reef, atoll).
- Reef growth is slow on a human timescale (millimeters to centimeters per year) and accumulates over thousands to millions of years.

If you want, I can show a diagram of reef structure or explain atolls and Darwin’s subsidence model.