Melithaea ochracea
A soft coral used in jewelry as red spongy coral.
Melithaea ochracea, a colonial soft coral from the family Melithaeidae, is better known as knotted fan coral. It forms tree-like, fan-shaped colonies on coral reefs across the South China Sea and is harvested for the jewelry trade under the name red spongy coral.
Colonies are arborescent, typically reaching about 20 cm (8 in) in length, though larger specimens exist. They grow in a single plane with a branching, fan-like structure. The main stalk and branches are jointed, with swollen nodes at the larger joints. The hard, calcareous internodes alternate with flexible, horny joints. A flexible membrane called the mesoglea, packed with tiny calcareous spicules (sclerites), covers the skeleton. These spicules—including capstans, double discs, disc-spindles, unilaterally spinose spindles, plain spindles, clubs, and anthocodial sclerites—are key for distinguishing this species from close relatives. Three sides of the branches are thickly covered with dome-shaped, perforated calyces from which the polyps emerge. Colony colors vary, typically in shades of yellow, orange, red, and white, sometimes with contrasting calyx and polyp hues. This coral lacks symbiotic algae (azooxanthellate). In Singapore, it grows near the low tide mark at depths under 3 m (9.8 ft), where colonies are larger and mostly have yellow branches with red calyces. Deeper, down to 15 m (49 ft), colonies are smaller and show different color combinations.
Its range includes shallow reefs from Taiwan to Indonesia, as well as Singapore and Malaysia. In Taiwan, it is the most widespread gorgonian coral, found on higher reef fronts where water flow varies from 4 to 40 cm (1.6 to 15.7 in) per second, allowing its numerous small polyps to feed.
In reef aquariums, it requires moderate water flow so its polyps can capture non-evasive zooplankton and likely phytoplankton. In jewelry, it is called sponge coral due to its porous structure. Bright orange-red pieces are most prized, but variegated specimens with yellow or orange streaks are also sought. Most commercial sponge coral is stabilized by filling with resin or polymer and polished; it may also be dyed, crushed, mixed with epoxy resin, and molded. It carves easily and is relatively cheap. Natural, unenhanced coral is more expensive but attractive rough material is scarce.
Quick Facts
- Taxon
- Melithaea ochracea
Facts from the source article.
Lore & Background
Colonies of Melithaea ochracea are arborescent and usually grow to about 20 cm long, though much larger specimens can be found. They grow in one plane and have a branching, fan-shaped structure. The main skeletal stalk and branches are jointed, with swellings at the larger joints; internodes are hard and calcareous while joints are flexible and horny. The skeleton is covered by a flexible membrane containing minute calcareous spicules, including capstans, double discs, disc-spindles, unilaterally spinose spindles, plain spindles, clubs, and anthocodial sclerites. Colonies vary in color—shades of yellow, orange, red, and white—sometimes with contrasting calyces and polyps. It is an azooxanthellate coral, lacking symbiotic algae. In Singapore, it grows near the low tide mark at depths under 3 meters, where colonies are larger and mostly have yellow branches and red calyces; at greater depths down to 15 meters, colonies are smaller with different color combinations.
Reader's Guide
Melithaea ochracea is significant for its dual role in reef aquaria and the jewelry industry. In aquaria, it requires moderate water flow to feed on non-evasive zooplankton and probably phytoplankton. In jewelry, it is known as sponge coral due to its porous structure. Bright orange-red specimens are most desirable, but variegated specimens with yellow or orange streaks are also sought. Most market sponge coral is stabilized by being filled with resin or polymer and polished; it is sometimes dyed or crushed, mixed with epoxy resin, and formed into shapes. It can be carved and is relatively cheap. Natural, unenhanced coral is more expensive but difficult to find in sufficient attractive rough material. With a Mohs hardness of 3.5, it is easy to work but also easy to damage; it should not be worn next to skin because it may become stained. Harvested in the South China Sea between Taiwan and Indonesia, it is sometimes farmed and grows much more quickly than traditional hard corals (Crallium spp.), with harvesting believed to be sustainable.
Did You Know?
- Melithaea ochracea is an azooxanthellate coral, meaning it does not contain symbiotic unicellular algae in its tissues.
- The coral measures 3.5 on the Mohs scale of mineral hardness, making it easy to work but also easy to damage.
- It is harvested in the South China Sea between Taiwan and Indonesia and is sometimes farmed.
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