How Can You Tell a Clam’s Age?

Have you ever collected shells at the beach, especially the large, flat, rounded ones that many people use as ashtrays? Well, those shells once belonged to the sea creature known as the clam.

At one time, two of those shells were fastened together and formed the home of the fleshy creature that lived inside. For years, scientists have not considered the clam a particularly unusual creature, but recently, a scientist at Princeton University, Dr. Ida Thompson, made a startling discovery. After ten years of research on clams, she found that the bands or rings on the clam’s outer shell indicates its age, just as the rings of a tree do.

Each year, the clam produces a ring on its outer shell. These annual rings are visible to the naked eye on the surf clam, but not on others like the quahog and the sea clam. Each ring’s width is slightly different from the next due to changes each year in the temperature of the water, the supply of food available to the clam, and the amount of oxygen in the water.

Because of these discoveries, Dr. Thompson believes that clam shells could provide science with a kind of “calendar” of the weather under the ocean floor over a period of years. Her studies have shown that some kinds of clams live as long as 150 years, but even the oldest of those studied showed no signs of old age and led active lives, active for a clam, that is.