Science for Everyone

Learning from Shells

Post by Scallop Research Intern, Bailey Moritz

Toni Chute and I start the task of aging the first scallop of several boxes of scallop shells

Bustling with research vessels and ocean scientists, Woods Hole, MA is a fitting location for the Northeast Fisheries Science Center, located right on the water. Toni Chute, one of their scientists specializing in all things scallops, was generous enough to give Cait and I a run-down on how to determine the growth of individual scallops based on their shells. Cait will be using these data as part of the collaborative scallop research project she is coordinating. Scallop shells are formed from calcium carbonate that the shellfish precipitates over the course of its lifetime. Depending on what region of the ocean it grew in, pigments vary, from a rich pink to deeper purple to the rusty red color seen on most scallops here in Maine. The shell-building material is laid down during a period of the year when conditions, such as temperature and food availability, are favorable. Then growth stops for awhile. This pattern creates rings, or visible line markings on the shells surface, that indicate each year of growth the scallop has undergone. By measuring the change in height between rings, you can elucidate how much the scallop grew from year to year. But be careful! As we learned, false “rings” can form if the shell cracked, or was damaged slipping through the large rings of scallop dragging nets when they were still below legal harvest size.

     Measuring a shell with each of the         growth rings marked off in pencil.

     Measuring a shell with each of the  
      growth rings marked off in pencil.

Determining growth rings can be a tricky task. The surface of some shells have a heavy cover of barnacles and limpets that make it difficult to see the patterns. Often times you can turn to slight changes in color to pin-point the rings, and getting the shell wet and holding it up to the light helps to bring that trait out. We practiced on a number of our shells collected from Muscle Ridge and were still somewhat hesitant in distinguishing between growth rings and cracks. But Toni reassured us that familiarizing ourselves with the shells patterns makes finding rings easier. It’s also perfectly alright to eliminate a shell from your sample if you’re finding it’s just too difficult to tell where the annual growth rings are. So, next time you come across a scallop shell on the beach or at the market, try your hand at finding the growth rings and you’ll be told a story about the creatures path from small spat to adulthood. 

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