Hard Corals

Hard corals are Hexacorals. This means that they have a polyp structure based on multiples of six segments. They have 6, 12, 24 internal partitions within each polyp. Their coral home is made of cement and reflects this architecture based on six segments. The cement coral home is known as a corallite. They are often very ornate. This is why many people use corals to decorate their mantlepieces and bathrooms. In my Marine Biology course, I explain the complex and beautiful corallite and how they vary in the fascinating world of hard corals.


Plate coral Mushroom Coral
A Black Tip Reef shark cruises over a plate coral and a branching staghorn coral. Plate corals are flat staghorn corals and provide shelter for fish. Plate corals seem to be growing broad to collect sunlight like a tree. This is because it gets 95% of its food from the microscopic brown symbiotic zooxanthellae algae that live with the fleshy tentacles of the polyps. Mushroom corals have strong ridges reminescent of the 'gills' of mushrooms. Like mushrooms, they do become active in the dark but they grow in sunlight using their symbiotic algae. Some divers like to pick them up or accidently kick them over. They must be placed right side up or the polyps will die. I try to turn them over when I find them upside down. The corals are very pale because, the algae have not been able to photosynthesise. Eventually, they die, if left upside down.
Staghorn Coral hard coral
Staghorn corals have complex architecture explained simply and clearly in my Marine Biology course. 5 or 6 polyps live on each bump on the staghorn coral branch. Each polyp lives inside a tiny hole called a corallite. These coral houses are sunken into pits on the tiny wart shaped bumps on the staghorn's branches. It is a most complex cement structure. To think that such a primitive lifeform can build such an amazing structure. This is an encrusting coral with large round polyps about 8 to 10 mm in diameters. The colony resembles a brain.