About Corals
© Michael Pitts / www.naturepl.com
What is coral?
Coral is the common name for a number of marine animals closely related to sea anemones, sea pens, jellyfish and hydroids. These groups are collectively known as the phylum Cnidaria, and are characterised by their simple body plan with two cell layers, and unique 'stinging' cells, known as cnidocytes, which are used for prey capture and defence.
Reef builders
Many stony corals have a special symbiotic relationship with zooxanthellae algae. The algae live and photosynthesise within the tissues of the coral, and help provide the coral with nutrients. Their partnership with zooxanthellae allows these corals to thrive in areas where the water is low in nutrients and to secrete large amounts of their limestone skeleton, forming large three dimensional structures. These reef-building or hermatypic corals are restricted to clear, shallow water, usually between 18 and 30°C.
A coral reef is the result of years of construction by the polyps of many coral colonies . Some of these reefs have been created over thousands, sometimes even millions, of years and are so big that they can be seen from space. Coral reefs may contain many different species of coral and support thousands of other species, making them one of the most diverse habitats on the planet.
Glossary
Cnidocyte: A cell housing a thread-like 'sting' called a nematocyst, unique to cnidarians. Used for prey capture and defence.
Colony, colonies (pl.): (relating to corals) Organisms, such as corals, which are composed of numerous genetically identical modules (also referred to as zooids, polyps or 'individuals'), which are produced by budding and remain physiologically connected.
Polyp: Typically sedentary soft-bodied component of cnidaria (corals, sea pens etc), which comprise of a trunk that is fixed at the base; the mouth is placed at the opposite end of the trunk, and is surrounded by tentacles.
Phylum: a major grouping in taxonomy
Symbiotic relationship: relationship in which two organisms form a close association, the term is now usually used only for associations that benefit both organisms (a mutualism).
Zooxanthellae: Dinoflagellate algae, all strains of the species Symbiodinum microadriaticum, which have a symbiotic relationship (a close association in which both organisms benefit), with some coral species.
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