Giant clam is the largest clam in the world. It can reach more than 4 feet (1.2 meters) in length. It can weigh about 550 pounds (250 kilograms).
The giant clam lives in much of the Indian and southwestern Pacific oceans. It is found mainly in coral reefs and tropical lagoons. Like other clams, it is a bivalve—a mollusk with shells made up of two parts called valves. The valves protect the soft body of the clam. See Clam.
The giant clam has a unique relationship with single-celled algae known as zooxanthellae. These algae live in the clam’s colorful mantle—a fleshy part of the body just inside the shell. The algae make food using sunlight, in a process called photosynthesis. The algae provide some of this food to the clam, and the clam gives the algae a safe place to live. This type of relationship is called mutualism. The giant clam also filters the water for plankton. Plankton are various tiny organisms that drift with the currents.
The giant clam reproduces by releasing sperm and eggs into the water. The fertilized eggs drift with the currents and develop as larvae (young). The larvae eventually settle onto the ocean floor. Adult giant clams are fixed in place. They can probably live for more than 100 years.
The giant clam has become rare or even disappeared entirely from some areas. It is threatened mainly by overfishing and habitat loss. People harvest the clams for food or to use their shells as ornaments, floor tiles, or bowls.
Some people believe that giant clams can clamp down on divers’ legs and eat them alive. But giant clams are physically unable to attack and eat human beings.
Several closely related species (kinds) of clam are also known as giant clams. These species do not grow as large.
