What Is Red Sponge Coral?

Written by reannan raine
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What Is Red Sponge Coral?
Coral grows in colonies in the sea. (texture of the sea coral. image by Olga Khoroshunova from Fotolia.com)

Red sponge coral is an organism that lives in the sea. It is bright red in colour and is harvested largely for the making of jewellery. Red coral jewellery is easy to find and inexpensive in spite of conservationists' concerns for the survival of this precious coral.


Red sponge coral (Corallium rubrum) is a filter-feeding invertebrate that creates a home from excreted calcium carbonate or protein. The coral colony is a culmination of generation after generation of these tiny organisms that continually add onto the structure made by the previous generations. Each coral takes on a form similar to a very small, bare tree with eight tentacles or branches extending out in all directions. Individual corals group together to make huge colonies or coral formations. Coral grows to between 50 centimetres and 1 meter.


Red coral colonies are either all male or all female. Reproduction is wholly dependent on the sperm released from a male colony floating or swimming over to a female colony. Fertilisation takes place internally. Larvae develop within the female's body cavity from the fertilised eggs and are released into the water after about 30 days. The larvae sink and attach to the substrate, adding to the formation. The whole process culminates in late July and August. Coral grows less than 1 centimetre per year, reaches maturity after seven to 12 years, and lives for 100 years. They consume tiny particles of organic matter by catching it with tentacles.


Bright red sponge coral grows in the Mediterranean and in seas around Japan. It can be found living in deep water around caves and under ledges where the bottom currents are strong.


Red sponge coral has been collected by humans for at least 25,000 years and used in jewellery for more than 10,000 years. Archaeological digs have unearthed it along with 25,000-year-old Paleolithic human remains and red coral amulets have been found in Switzerland that have been dated to 8000BC. Originally, it was gathered from beaches after heavy storms washed it ashore. Harvesting was started 5,000 years ago by Greek fishermen.


Red sponge coral is one of the most highly sought-after corals. Red coral is used extensively to make jewellery. ("Although rather soft by gem standards, they are reasonably tough and take a high polish," according to Barbara W. Smigel, PhD, GG.) The jewellery is primarily made in China, Japan and Italy. It is not generally expensive jewellery. A pair of red coral and sterling silver earrings can be purchased for around £32. It is also used as an art medium for carving.


Red sponge coral populations have been severely depleted over the years. Conservation efforts are ongoing on behalf of this precious coral. "Corallium has been intensively harvested for centuries, and both landings and population data provide strong evidence that most commercially viable Corallium beds are now depleted," according to Andy Bruckner of the National Oceanic and Atmospheric Administration Fisheries.

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