Pearls, valued as jewellery and precious stones, are produced by oysters when an irritant enters their body. While pearls over 80 years old may have been taken from wild oysters, because pearls only occur in only 1 in 10,000 oysters, all commercially sold pearls are cultured in a lab.
Pearls are actually the oyster equivalent of an ulcer, and like human ulcers, they are the result of stress or irritation. An irritant is injected into the body of the oyster, and the oyster responds by coating the irritant with layer upon layer of nacre, which is what we call Mother of Pearl. Fewer than half of oysters survive this process, and those who do are usually re-inserted with irritant. Cultivators purposely stress oysters by suspending them in different temperatures and shaking their cage to speed up the process.
While oysters are animals, they do not have central nervous systems and so they are unlikely to experience pain in a way resembling ours. However, there is simply no way to know this for sure, and just because their experience of stress and pain does not resemble ours, it does not follow that their experiences should not be taken into moral consideration. Oysters are clearly aware in that they do respond to stress and environmental changes, as this is the entire basis for the practices employed by the pearl industry.
When we weigh up the potential harm caused against the gain, considering that pearls are by any reasonable definition an unnecessary luxury item, putting oysters through this process is unjustified. Given that synthetic pearls are widely available and are of sufficient quality to be indistinguishable from natural pears to anyone who is not a trained jeweller, there is no good reason to buy pearls that are farmed from living animals.