From fiery oranges to delicate purples, the colors of seashells are one of nature's most beautiful works of art. We often marvel at these hues while walking the shores, but have you ever wondered how these shells have such beautiful colors and patterns? The answer is a fascinating mix of biology, diet, and environment.
Shell colors aren't painted on after the shell is finished, they are woven into the structure of the shell as it grows. This happens with the mantle, the specialized organ responsible for building the shell's calcium carbonate structure. (To learn more about the mantle and it's role, check out this blog post on how seashells are made).
Within the mantle, there are pigment-producing cells. As the mantle secretes layers of calcium, it also releases liquid pigments. These pigments bind to the protein matrix of the shell, essentially dyeing the calcium as it hardens.
The specific colors and patterns you see are rarely accidental. They are influenced by three primary factors:
1. Genetics
Just like us, mollusks have genetics! Heredity determines the shell's "baseline" colors and patterns for a species, ensuring that a conch looks like other conchs, etc.
2. Diet
Just like a flamingo turns pink from eating shrimp, a mollusk’s shell color is heavily influenced by what it eats. The pigments found in the algae, sponges, or prey the mollusk consumes are processed by its body and deposited into the shell. If a mollusk’s food source changes abruptly, you might even see a color shift in the growth rings of its shell!
3. Environment and Sunlight
Environment and sunlight play a major role in the vibrancy of a shell. Creatures that live in shallow, sun-drenched areas often have much brighter colors and more complex patterns. In the dark, deep ocean, shells are often solid colors and darker tones. The lighter and darker colors help camouflage the animal to blend into its environment. A shell's colors can also be affected by the sediment it is buried in, which is why you may find darker greys and blacks.
But, how do shells get their patterns? Once again, the mantle is responsible for this! As a mollusk grows, the mantle acts like a biological inkjet printer, depositing pigment line by line along the shell's margin. This can form solid bands, vertical stripes, and dots and dashes depending on the mantle's design. Because a shell only grows at its edge, the patterns we see are actually a time record of that animal’s growth history!
Since the colors of a shell are organic pigments, they are sensitive to UV light. In the ocean, the shell is often protected by a thin, skin-like layer called the periostracum that preserves its color and pattern. Once that wears off and the shell is exposed to the harsh sun on the beach, the organic bonds in the pigment break down, and the color slowly bleaches away.
The next time you are combing the beach, stop and appreciate the amazing variety of colors and patterns you see. They are truly a unique, one-of-a-kind work of art!