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Pearl Grafting
When the nucleus is implanted into the mollusk, a small piece of mantle tissue is placed alongside the nucleus. When the outer cells of the mantle tissue, called the ectoderm, come into contact with a foreign object, the nucleus, they rearrange themselves around it and eventually form a sack in which the pearl will develop. Glands that secrete nacreous substance also begin to form. The whole process takes 1-2 weeks, depending on the temperature of the water.



Knowledgeable grafters are able to select mantle tissue from the correct location near the rim of the outer mantle that contains cells that will produce nacre immediately. These cells are young and produce smaller aragonite platelets, which will in turn produce a higher degree of luster on the finished pearl.

Formation of the platelets as well as any conchioline layers that develop are a result of the individual mollusks reactions to the foreign object and its immune system’s reaction. The farmer’s goal is to influence the development of the platelets, which form the pearly layer, to begin growing immediately and smoothly throughout the pearl’s formation. Success can be determined via x-ray, which has shown a significant decrease in cultured pearls with layers of conchioline thanks to improvements in culture technology.

By 1969, experiments by Dr. Koji Wada of the national Research Institute of Aquaculture also proved that it is possible to influence the color of the finished pearl through proper selection of mantle tissue. All these techniques are not absolute however, environmental factors which are impossible to control have a strong effect on the health of the mollusk and subsequently, the development of the pearl.

There are many factors that influence the growth rate of a pearl including temperature, the time of the year, and even the time of the day. Fluctuating temperatures have serious effects on the mollusks’ health. Cold temperatures in particular cause the mollusks to retreat into hibernation, sometimes halting their metabolism entirely. When the growth rate is merely slowed however, the platelets that form tend to be smaller, producing a higher luster. Because of the effects the seasons have on the mollusks, many farmers move them to different locations throughout the development process.

Once the nuclei are inserted, the mollusks require about six weeks under close observation. Some do not survive the insertion process, while others reject the foreign object. After six weeks, the remaining mollusks are examined via x-ray to ensure that the nuclei still remain. Next, they are placed underwater, either in baskets or strung onto ropes, suspended from rafts. Mikimoto himself observed that vertically placing the mollusks for the long term growth period produced better results.

In the early years of cultured pearl farming, pearls were left to grow for three to six years, forming pearls with a very thick nacre, up to 0.9mm. By the end of World War II, growth times were decreasing, though three years was still considered the minimum. Small nuclei were beginning to be left in for only a year, and 5-6mm nuclei were only given two years to grow. On average, pearls in this time period showed a decrease in quality.

In the 1990s, mollusk mortality rates began to reach an all-time high. Farmers in Ago Bay were found to be hanging more baskets than allowed from each raft, claiming that they did not have enough space to spread them out. Many farmers were unwilling to deal with the risks of the longer pearl growth, even if it meant a bigger return. The costs of maintaining the farms are high, and there were a great number of environmental risks that could easily destroy years of hard work.

One of most critical aspects of maintaining a successful pearl farm is being constantly aware of the environment and the effect it can have on the mollusks. Sudden shifts in temperature can kill the mollusks, so weather and water temperature must be carefully monitored. The circulation of plankton in the water and the strength of water currents is also measured to ensure that the mollusks are able to get the proper nutrition. Extreme weather, such as typhoons or excessive rainfall, which lowers the salinity of the water, can be disastrous.

Probably the most-feared risk factor is the red flood. It is difficult to predict, and requires immediate action to remove the mollusks, which can be killed in a matter of minutes. The flood itself is sparked by an abnormal change in the plankton, which causes micro organisms to reproduce and die at an incredible speed, poisoning the water. These floods can last anywhere from days to years, and are impossible to fight or control.

The mollusks themselves have natural enemies in the water as well, such as eels, squids, and sea stars, some of who are small enough to even infiltrate the baskets.

Water pollution is an increasing concern, as containments from the cities and industrial compounds find their way into the water off the shores. The pearl farms themselves generate a large amount of natural waste from the mollusks and the organisms that attach themselves to the shells, which now layers the ocean floor beneath the farms and can kill plankton necessary to the mollusks’ survival. Strategies to deal with the pollution issue have been suggested but not put into effect. Scientists are also still investigating the factors that could have lead to the highest mortality rate of mollusks on farms in 1996.   

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