A Second Life for Shells

Farmers do not throw away empty shells after harvest. In fact, you may have products made from shells in your home.

What Are Shells Made of?

Blue mussel with debris and mud covering part of its blue-black shell.

© Ale1969/Dreamstime

Shellfish draw calcium and carbon from water. They use these materials to make calcium carbonate to build their shells.

How Is That Good for the Environment?

Once the carbon is locked into their shells, it does not return to the atmosphere. This is how shellfish capture carbon, which helps fight climate change.

Reducing Soil Acidity

Green tomatoes with rotting, brown-black bottoms, hanging from the vines of a tomato plant.

Kristi Blokhin/Shutterstock

In the 1800s and 1900s, farmers in Prince Edward Island used “mussel mud” as a substitute for lime, to reduce the acidity of their soil. Mussel mud is rich in calcium carbonate, an alkaline mineral released by the decomposition of shells.

Today, shellfish shells are used to fight both soil and water acidification. When soil becomes too acidic, many plants can’t absorb the nutrients they need to grow.

Calcium Supplements

Blue bottle of pills labelled “CALCIUM 600 mg + D.”

Donna Beeler/Shutterstock

Some calcium supplements contain oyster shells. The ground-up shells are a good source of calcium carbonate.

Heartburn Relief

Variety of pills in different colours and shapes against a white background.


Some heartburn medicines contain oyster shells. Calcium carbonate is an effective antacid.

Chicken Feed

Hen poking her head into a feed tray with a metal guard, with other hens doing the same behind her.

Thomas Shanahan/iStock

Calcium can help chickens grow! When ground-up oyster shells are fed to hens, the calcium carbonate in the shells helps them form eggshells and strengthens their bones.

Shells in Aquaculture

Black-and-white photograph of a man attaching long lines threaded with oyster shells to a metal bar, with piles of similar lines behind him.

Preparing oyster shells for spat collection, Eskasoni, ca. 1980. Beaton Institute, Cape Breton University

Shellfish farmers, including Indigenous ones, used scallop shells to collect oyster seeds for farming.