Did you know that only the top layer of a coral reef has living polyps? As new layers are added, the polyps leave the lower layers.
Photo: Nick Hobgood/Wikimedia Commons.
Coral reefs are called ‘rainforests of the oceans’, hosting a large community of living organisms – fish, plants and many other creatures including sponges, oysters, and sea anemones.
The main living structure is the reef itself which is made up of tiny animals called polyps that stay fixed in one place. The colony starts when a planktonic (free floating) coral larva settles on a hard substrate. Immediately after settling, the larva changes into a polyp.
This founder polyp then divides over and over to form the colony. Thus, all the polyps in a coral colony are clones (genetically identical copies) of a single founder polyp with connected digestive and nervous systems. These polyps lie in a self-made cup-like skeleton of calcium carbonate.
Over the years, a series of polyps, continually add layers of calcium carbonate, building a skeleton that can take many different shapes depending on the species involved. Each polyp is connected by living tissue to form a community. The living tissue is only a thin layer on the surface. It is the constantly growing calcium carbonate structure that creates the coral reef.
Coral polyps are small and simple looking. Each polyp has a ring of tentacles shaped like a cup around a central opening. These long arm-like tentacles have stinging cells. Like sea anemones, the tentacles are used to capture food, usually extremely tiny larvae of various crustaceans and molluscs, called zooplankton.
First appeared in: Sanctuary Cub, September 2013.