Glittering diamonds, sparkling（发火花） gems（宝石） and precious pearls. Essential for any crown（王冠）. And true gifts from nature. So we'll give（做） that a bit of a wash with water. A beauty. Extracting（提取） these treasures often means exploitation（开发） and environmental damage.

  But there is another way to make（使） jewelry. If we look after nature, it looks after us. And nature can also instruct（指导） us in its treasures. If you know how it's done, you get a diamond at the end. So how does ethical and environmentally-friendly jewelry manufacturing work? The water is ice-cold.

  But for the nature conservationists, that's all in a day's work. Here's one, and another one. Here they are. They seem to like it here. They lie nestled（舒适地坐定） in the bed of this small stream. Freshwater（淡水） pearl mussels（蚌）, a delicate（纤细的） marvel of nature.

  The conservationists are in eastern Germany working to protect the mussels from extinction. They're important for the ecosystem, but not because of their pearls. Freshwater pearl mussels have existed on this planet for 230 million years, so they've seen a lot. It's one of the oldest species in the world today. Freshwater pearl mussels have seen the dinosaurs come and go. But now it's us humans who might be the ones to drive them to extinction.

  An aquascope helps the researchers have a clear（清晰的） view underwater. Rebecca Höss uses a detector（探测器） to locate the mussels（蚌） that have been tagged with a tiny microchip. That helps the scientists keep tabs on the mussel population, which they monitor once a week. This allows us to tell what kind of mussel it is without having to remove it from the stream, which would stress the mussel. But to make sure it's still alive, we do have to take them out once a year. The numbered microchips are attached to the shell with dental cement.

  There it is. The day is correct, and it's still where we left it. Super. Perfect. A few thousand years ago, the streams here were full of mussels. There are still people alive who remember that after the war, the mussel beds here were three layers deep.

  When they looked at the bed of the stream, it looked totally black. That's how many mussels there were. The pearls that can be found in this part of eastern Germany were first documented in the 15th century. The huge mussel population attracted pearl fishers in large numbers. But only one shell in every 2,000 mussels had the treasure nestled inside it. A news report from the 1960s is a testament（遗嘱） to that history.

  The eye of the law keeps watch. The fishing trip takes place under the supervision（监督） of the mayor. This pearl is said to be as valuable as the treasures fished from the South Pacific and the waters around Australia. The pearls were sought after by kings and queens as a symbol of power and wealth. But today, the mussels themselves are the treasure. A single mussel can filter（滤过） more than 100 liters of water a day, helping to keep the stream clean and healthy.

  But now, dry summers and intensive（加强的） farming are destroying their habitat. These days, the streams are often bordered by farmland rather than meadows. Soil makes its way into the water and ends up as mud. But the mussels can only thrive（兴旺） on a loose bed of gravel（砂砾）. It's a huge problem for young mussels, of course. The mud starves their habitat of oxygen.

  The young mussels end up covered in mud and suffocate. The young mussels die, leaving only a few adults, so few that hunting for pearls would drive them to extinction. What you see here is kind of like a hospice. The population in the stream is aging. You can imagine them as all middle-aged, 50 and up, without any young mussels at all. That's our biggest concern right now, and why we're breeding（使繁殖） pearl mussels（蚌） so that we can replenish（补充） the stream with young ones.

  It's the only way the conservationists can rescue the endangered species. The next batch of young mussels is ready to be moved into the stream. On the other side of the world, the South Pacific is home to pearl oysters（[动]牡蛎）. This species isn't endangered, so cultivating（培养） pearls here is viable（能养活的）, and it can also be sustainable. There's a huge oyster farm beneath（在……下面） the surface of the water, with thousands of oyster nets on ropes that extend for kilometres. Marine biologist（生物学家） Justin Hunter is an expert on these delicate（纤细的） ocean dwellers（居住者）.

  He's been farming the species Pingtada magaritifera for 20 years. Pearl aquaculture requires patience and a delicate touch. That's because every cultured pearl begins with a grafting procedure that mimics（模仿） what would normally be a natural process. We don't want to overstress them. This operation, of course, is quite a bit of stress, but we try to handle them as gently as we can. They are living animals.

  That's why, you know, they're kept wet, they're quickly washed, cleaned. They'll go through this process very fast and then be back into a recovery tank and then taken back out to the sea. Masura Dongallu is the most important member of the team. He carries out the grafting procedure on the oyster, which induces（劝诱） pearl formation by imitating a natural process. First, he extracts a tiny piece of mantle（斗蓬） tissue from a donor（捐赠者） oyster（[动]牡蛎）. That tissue is then implanted into the recipient（容器） oyster（[动]牡蛎）, along with a tiny mother of pearl nucleus.

  In a natural defense mechanism, the oyster will form what is called a pearl sac around the foreign body. Over time, the nucleus is covered with what is called nacre, layer by layer, creating a pearl. Hunter's client Jürgena travels from Germany to Fiji every three or four years to buy pearls. Here's the oyster that's already been implanted with the nucleus and the mantle tissue. The tissue will grow around the nucleus and over two years cover it with 2,000 delicate layers of nacre, mother of pearl. With any luck, the end result is a perfect pearl.

  Yeah, it's not a short process at all. But not all pearl cultivators are as patient as Justin Hunter. Many oyster farmers in Asia fatten（ 长胖） the shellfish（甲壳类动物） with organic waste from chicken and pig farming. The overfed oysters produce up to 60 pearls. After the harvest（收割） they die and this form of mass production is harmful to the environment. In Fiji, the oysters are returned into the sea for at least 18 months after they are seeded.

  Many stay longer to allow time for the pearls to grow, a single one per oyster, not 60. So now we're going to see the farm where the pearls come from, in paradise. Our work team and what they're working on now are oysters that will be implanted over the next couple of months.