Black corals

Only a few species of coral have a combination of beauty, hardness, and luster, such the black coral species of Hawaii (Antipathes dichotoma and Antipathes grandis). These are highly valued by the jewelry trade. There are also a few red. pink. gold, and bamboo varieties that are in demand. Black coral also occurs in the Gulf of California and in the Pacific Ocean off Baja California, plus a few scattered locations in the Pacific Ocean east of Australia and north of New Zealand. Traditional sources of red and pink corals have been the Mediterranean Sea, various locations in the western... 

Decorative coral is usually one of the hard corals. They are described by color, rather than by species, and live in tropical and temperate seas. The traditional orange or red precious coral is native to the Mediterranean and has been severely over-collected for hundreds of years. Most red coral on today s market is dyed coral from the Pacific Ocean. Black coral is a branching, tropical type that is also rare. There are a number of corals that are collected and sold today as black coral, but it is often merely dark-colored coral that has been dyed black. 

There have been few real simulants of horn as supply is plentiful and the material is relatively inexpensive. However, it is not cheap to work as it must be hand crafted, so today it is regarded as a luxury item. Horn has itself been used as a simulant of other materials, most notably tortoiseshell, black coral and jet. 

These corals come predominandy from the Malaysian archipelago, the Red Sea, the Mediterranean and New Zealand. Ibere are several types of black coral used for jewellery. They have skeletons made of a homy material instead of calcium carbonate. 

It can be extremely difficult to tell the various black corals apart, even in their rou form, unless the whole coral is present. Phen made into jewellery or carvings, the task is often impossible. 

Most of the black corals used belong to the order Antipatbaiia (Fig. 11.14). They can be branched or tinl andied, and they have concentric layers of homy material around a central canal, which may be very fine C e same applies to golden corals of the order Andpatfaaiia (Figs 11.17 and 11.18)). Common to the antipathaiians is that th all have spines. Most of these are minute and, in many cases, are only present... 

Another Mediterranean black coral is Gerardia, of the order Zoanthiniaria. It is brownish to black, with a smooth surface, and can grow to 2 metres tall with a very sturdy trunk . It has been known and used for centuries. 

Both antipatharian and gorgonian corals can also occur in golden varieties. Here there is even more difBculty in identifying the species with absolute accuracy as black coral can be bleached to a golden colour. The bleach can permeate quite deep into the coral, and it can be impossible to tell without complicated tests - srtiether the golden colour is natural or bleached (Figs 11.17 and 11.18),... 

Figure 11.18 Golden antipatharian coral necklace. Possibly bleached black coral.

Black corals that consist of a homy material can be bleached with hydrogen peroxide - in much the same way as can human hair, which also consists of a homy material. The resulting coral resembles golden corals, which are more rare than black. The effect does not penetrate to the core, but it is very convincing, and thus difficult to identify without cutting into the material. 

Jet would not be used to imitate black coral, but, when polidied, the two could be confused. No structure will be visible on the polished sui ce of jet, but growth rings and other structures may be visible in coral. 

Black coral can take a high polish, but in some species it retains a natural sheen, and, viewed through a lOx lens, displays a structure of tiny bubble-like bumps on the surface. 

Polished black coral can be conhised with polished jet. The latter shows no structurej while signs of growth rings may be visible in polished coral (Fig. 11.16). However, breaks or chips in the material may help with identification. Black coral s fiacture is splintery, while that of jet is conchoidal. 

A rubbed or abraded area that looks dark, in an item apparently made of golden coral, indicates bleached black coral. However, this material is difBcult to identify, as the bleaching usually takes place after working, so even the drill hole in a bead will be bleached (Figs 11.17 and 11.18). 

The rules governing the conservation of the various corals are constantly changing, and many are now protected species and may not be collected at all. In some areas there is a quota for collection. At the time of writing, blue coral, Heliopora coendea, and some black corals are listed on CITES Appendix II, which means that their trade is covered by very strict controls. Sadly, the controls are not always effective, and there is also a certain amount of poaching. Further, for many species of corals the controls are not nearly stringent enough and whole areas are legally harvested until they are bare. 

It is known that black coral was being made into bracelets by the people of the Malay Archipelago in the mid-eighteenth century. They soaked it in coconut oil and heated it gently to form it, and sometimes inlaid it with gold for use by their chiefs. This treatment would have been possible because, being a homy material, it would be to some degree thermoplastic. 

B From Coska Maya, arrange a trip to snorkel the largest coral reef in Mexican waters. Banco Chinchorro lies off the coast of the southern Yucatan and is home to rare black coral, sea turtles and moray eels. 

Nowak, D., Florek, M., Nowak, J., Kwiatek, W., Lekki, J., Zieba, E., et al., 2005. Micro-spectrometric investigations of inoiganic components of the black corals for biomedical applications. Key Eng. Mater. 284—286, 297-300. 

Figure 17.1 Digital photos taken by ROV Holland I during NUI Galtvay cruise CE13008 aboard RV Celtic Explorer. Clockwise from top left giant hydroid at approximately 1500 m depth, Acesta excavata (-600 m), crinoid (1200 m), black coral (1200 m). Laser dots (where shovm) 10 cm apart. All photos copyright Marine Institute. A black and white version of this figure will appear in some formats. For the colour version, please refer to the plate section.

Three 20- and 22-carbon atom polyethylenic adds, bearing a hydroxyl group on carbon 8, were isolated from a black coral, a zoantharian of the genus Leiopathes whose spedes name is now Leiopathes glaberrima. These acids are probably derived from arachidonic acid and eicosapentae-noic acid (EPA), and fall into the category of oxylipins. 

The atypical sterols of Hexacorallia are polyoxygenated sterols similar to those usually encountered among Octo-corallia, but published work almost exclusively concerns only the orders Antipatharia and Zoantharia. The black coral Antipathes subpinnata has yielded about 10 polyoxygenated sterols without polymethylated side chains, but their principal characteristic is the presence of a hydroxyl group on one or other of the angular methyls at C-18 or C-19 (Aiello, Fattorusso, and Menna, 1991,1992). Most of these steroids are toxic to the shrimp Artemia salina. Some structures are shown in Figure 20.67. 

Antipathine A is a new carbazole alkaloid isolated from the Chinese Black Coral Antipathes dichotoma, and tubas-trine and tubastraine are two uncommon nitrogen-containing aromatic derivatives isolated from Tubastrea aurea and T. micrantha, respectively. No particular biological activity was mentioned for these compounds. 

Aiello, A., Fattorusso, E., and Menna, M. (1991) Five new polar sterols from the black coral Antipathes subpinnata. Steroids, 56, 513-517. 

Al-Lihaibi, S.S., Ayyad, S.-E.N., Shaher, F., and Alarif, WM. (2010) Antibacterial sphingolipid and steroids from the black coral Antipathes dichotoma. Chem. Pharm. Bull., 58,1635—1638. 

Guerriero, A., D Ambrosio, M., and Pietra, F. (1988b) Leiopathic acid, a novel optically active hydroxydocosapentaenoic acid, and related compounds, from the black coral Ldopathes sp., of Saint Paul Island. 

Nanjiols A-C are other examples of conjugated sterones that have been isolated from the species Nephthea bayeri, harvested near Nanji Island, in the east of the China sea (Shao, Zhu, and Guo, 2002). These conjugated 1,4-diene-3-ones have structural similarities (20S-hydroxy) with some of the sterols of the hexacorallian Antipathes sub-pinnata, better known as the black coral (see below). Nanjiols do not possess significant cytotoxic activity. 

---