标签：over tag alter ann jewel end man real group
珊瑚中最具价值的是贵珊瑚，PreciousCorals贵珊瑚又被称为红珊瑚，它们的骨质比较致密，硬度和象牙非常相近，色泽有红色、粉红色和橙红色等，适合加工成为华美的珠宝或高级艺术品，深受世界各地人们的喜爱。 “precious corals,” are deeper-water, branching cnidarians that have been used for thousands of years to make beautiful beads, idols, and expensive jewelry. Interestingly enough, this group secretes an endoskeleton that is considerably harder than the exoskeletons of the so-called hard corals.
There are four types of precious coral in Hawai‘i: black coral (Antipathidae), gold coral (Parazoanthidae), red or pink coral (Corallidae) and bamboo coral (Isididae). Each of these has a different internal skeleton. Red and pink corals produce a calcite skeleton similar in hardness to ivory and pearls. Bamboo corals, on the other hand, produce a skeleton composed partially of calcite and partially of protein that is similar to the keratin in your fingernails. These alternating bands of material resemble a bamboo stalk; thus the corals‘ name.
Black and gold corals secrete only protein and no calcite. In addition, gold coral is a parasite, whereby its larval stages settle out on other species of corals, particularly bamboo corals. Eventually, the gold coral overgrows the entire bamboo “tree,” incorporating the bamboo coral‘s skeleton as the core of its own skeleton. Gold and bamboo corals also have another interesting characteristic: They are bioluminescent. These corals light up in a beautiful show of sparkling blue lights when mechanically stimulated, such as when the current is strong or when a crab walks down one of their branches. Perhaps it attracts the small animals they feed on; no one really knows for sure.
Harvesting Methods
Precious corals have been harvested in a number of ways. For centuries, fishermen dragged nets over the sea floor, which broke and entangled the coral trees so they could be hauled into a boat. Because this method can impact other marine life attached to the sea floor, dredging and drag netting are now banned in the United States. The nation‘s precious corals are harvested by permit and only with selective methodologies.
In Hawai‘i, black corals are found in 100-300 ft of water, shallow enough to harvest using scuba equipment. Many harvesters, however, have died in pursuit of coral trees at the deep end of this range. Red, gold and bamboo coral are found between 1,000 and 1,500 ft; harvesting is conducted with remotely operated vehicles (ROVs) or submarines.
英语preciouscorals贵珊瑚PreciousCorals红珊瑚
标签：over tag alter ann jewel end man real group
原文地址：https://www.cnblogs.com/tolearn/p/11629567.html
