Bivalves: The Filter Feeders Worth $1 Billion a Year to the U.S.

Clams, oysters, mussels and scallops look simple — a soft-bodied animal inside a two-part hinged shell — but they filter the water around them, build their own homes as they grow, and live in almost every part of the world ocean. They are also valuable: NOAA estimated the 2011 economic value of commercial bivalve harvesting in the U.S. at about $1 billion annually.

A roughfile clam from the Flower Garden Bank National Marine Sanctuary, one of many bivalve species. Credit: NOAA.

How a bivalve lives

• Breathing. Like fish, bivalves breathe through their gills.
• Feeding. They are filter feeders, and they gather their food through those same gills.
• Moving. Some have a pointed, retractable "foot" that pushes out of the shell and digs into the sediment, letting the animal move or burrow.

A shell that grows with its owner

Bivalves make their own shells. An internal organ called the mantle secretes calcium carbonate, so that as the soft animal inside grows, its shell grows into a roomier home.

Everywhere in the ocean

About 9,200 species of bivalves are estimated to exist, and together they live in virtually the entire world ocean: from the warm tropics to the sub-zero Arctic, and from the deep ocean to sandy and rocky shorelines. A few have even settled around hydrothermal vents deep in the Pacific Ocean, below 13,000 feet.

Wherever they live, many play important roles in their ecosystems. They filter the water, and they serve as habitat and prey for a wide variety of sea life.

What they are worth

Beyond their place in the ecosystem, bivalves are big business. NOAA estimated the 2011 value of commercial bivalve harvesting in the U.S. at about $1 billion annually, with a harvest weighing an estimated 153.6 million pounds.

Sources

Based on "What is a bivalve mollusk?" from NOAA's National Ocean Service, a work of the United States government in the public domain.