Seashells on the Seashore
Have you ever wondered why seashells are different colors? I have, and I finally decided to do some research and learn why.
Seashells are the remains of sea mollusks that washed ashore, some small, some larger. Their shells are made mostly of calcium carbonate along with a little protein. The calcium carbonate portion is made by calcium ions secreted from the cells of these little creatures and the carbonate ions present in the water. Another interesting fact is that the seashell grows outward, so the newest part of the seashell is the outer edges.
If you’ve enjoyed the various colors of seashells, you know that there are many assortments, not only in the type of shells (mollusks) but in the assortment of colors. The colors of a seashell often camouflage it, thus enabling these small critters to hide from their predators. But their different patterns and shell coloring also become a means by which the different species communicate with each other.
So, besides camouflage and communication, why do they display a rainbow of colors? The shells are composed mostly of calcium carbonate (CaCO3), which is also found in rock, eggshells, and pearls. I’m sure you’re also familiar with it as the main cause of hard water. But what color is CaCO3? It’s white. Not ALL seashells are white, are they? I have found a few beautiful pure white seashells; but from my shell collecting, they are rare. The color or coloration of the seashells is dictated mostly by the diet of the mollusk and the water environment in which the creature lives. Impurities and waste from the organism are captured in the shell when it is formed, thus adding more variation to its color. The food the mollusk eats causes it to produce pigments in the mantle covering (layer) of the mollusk. If the pigment is secreted continuously it creates a spiral or radial band of the shell (see picture to the left) but if it is periodic the shell develops sports or flecks. It is also interesting that shells that are red in color usually have carotene or what is called pterodines in them. Shells that have brown or black hues have melanin in them.
You may also be thinking about the iridescent shells that are multicolored and shiny. It is a different process that creates that effect. This iridescence is called mother-of-pearl and is caused by a coating of nacre on the shells, which is secreted by oysters and some other mollusks to protect their bodies from parasites and disease. This coating is usually very thin, in the range of several hundred nanometers thick, yet it is very strong, very resilient. The nacre is also the same substance that composes pearls.
So, as you can see there’s a lot more that goes into a seashell than you may have considered. Next time you’re at the beach, take a closer look at the seashells spread across the sand in front of you. Indeed God has created some fascinating examples of His infinite creativity and beauty, and we are the beneficiaries.
Here’s some beautiful and colorful seashells I collected from North Myrtle Beach, SC earlier this month. Notice the variety in colors.