The Angry Oysters Collective: Pearls Are Produced by Irritated Mollusks

In the center of a famous Vermeer painting, pearls have long been prized as jewelry. Yet they do not form from the Earth’s depths; they grow inside the protective shells of mollusks.

Mother-of-Pearl Spheres

The shells of mollusks, with their soft and slimy bodies, are their main line of defense. But when pathogens manage to breach them, these creatures employ a remarkable strategy to trap them. By absorbing calcium carbonate found in the surrounding water, they can produce aragonite, which, when bound to a protein known as conchiolin, ultimately forms a nacreous sphere with a distinctive luster.

To obtain large quantities, the jewelry industry relies on farming. Generally, oyster farmers manually insert a small foreign object (such as a fragment of glass or plastic) inside the oyster’s shell before returning it to the water. It will take up to five years to yield a fully formed pearl.

Among the most sought-after is the black pearl, with anthracite or dark green hues, produced by the Tahitian black-lipped oyster. While pearl oysters produce them less frequently, they can still be genuine giants.

For these bivalves, the official record is held by the species Tridacna gigas, with a pearl weighing over 27 kilograms found in the Philippines in 1959. Not confirmed by Guinness World Records, a specimen weighing 34 kilograms, known as the Puerto Princesa Pearl, was discovered in 2006 in the same waters by a fisherman.

A Not-So-Radiant Future

Like many marine species, climate change poses a major threat to mollusks.

In the coming decades, the warming of the seas and ocean acidification, linked to rising atmospheric carbon dioxide levels, could push these creatures to devote more of their resources to strengthening their shells, thereby reducing the nacre available for pearl production.

In case you didn’t know, the oldest animal on Earth was a mollusk, which tragically died at the age of 507 years.