Giant Clam

ID points

• Two heavy wavy shell edges clamped tight onto the reef
• Mantle patterned in brilliant blue-green or golden brown
• When startled the mantle snaps back and the shell closes

Basics

Family

Tridacnidae

Length

50–120 cm

Depth

1-20 m

Regions

Indo-Pacific reefs

Distribution

Shallow tropical coral reefs from the Indian Ocean to the Pacific

Habitat

Shallow reef flats, embedded in coral

Diet

Sugars from symbiotic algae, plankton

Easily confused with

Soft CoralNo stony skeleton, soft and springy to the touchSea FanA fan-shaped mesh skeleton growing perpendicular to the currentTube-dwelling AnemoneLives in a long soft tube of its own making

Fun fact

The giant clam is the largest bivalve in the world, reaching 1.4 metres across and 300 kg in weight, and living for more than 100 years. The iridescent blue, green and purple of its mantle comes from the billions of symbiotic algae living inside it. It gapes open in the sunlight so those algae can photosynthesise and supply most of its food.