Marine Biology Notes: Oysters and Pearl-making

Calcium carbonate (CaCO3) = chemical that makes pearls
Chemical compound available in both land and aquatic environments, the latter more than former
Earth’s crust stores heavy amounts of calcium
Rivers and oceans have taken in layers of calcium deposits 1000+ years old
Atmospheric CO2 + seawater → dissolved carbonate
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Hydrothermal vents (heated seawater + salts high in calcium) → accelerated rate of calcium washing into Earth’s waters
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Step 1: Oysters begin as unshelled larvae →
Step 2: Mantle tissue produces molecules like proteins to build scaffold-like structure →
Step 3: Oyster separates calcium & carbonate from seawater in filtration syst’m →
Step 4: Calcium and carbonate fuse into calcium carbonate →
Step 5: Electrically charged proteins carry calcium carbonate over the scaffold so they start forming shell layers →
Step 6: Oysters apply specific proteins to converting CaCO3 into aragonite & calcite, 2 crystal structures
Aragonite & calcite differ from one another in their characteristics despite sharing same chem compound b/c each mineral’s crystal lattices are organized differently
Calcite exhibits greater stability than aragonite; less vulnerable to gradually dissolving
Oysters, like other mollusks, rely on calcite for their shells’ hard outer layer
Aragonite solubility gives it advantageous survival in surroundings of various levels of acidity
Aragonite makes up oysters shells’ inner layer → oysters’ internal pH levels stabilize
Process of layering aragonite repeatedly and spreading the mineral out w/ proteins → Oysters create nacre (a distinctively strong form of aragonite)
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Nacre, put under a microscope, is structured as rows and columns of hexagonal bricks → iridescent effect occurs; layers’ thickness mimics visible light’s wavelength
Particles of light that penetrate nacre ricochet within its crystalline, brick-stacked composition, rendering as rainbows
The cells needed to make it protect other mollusk organisms against parasites or foreign objects like stray sand via a coating the mollusk generates
Wrapped intruders in proteins and aragonite are called “pearl sacs” → unwanted object/organism gets dissolved into a pearl

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