The giant clam, Tridacna gigas, is the largest species of bivalve mollusc in the world, reaching more than 1.2 meters (47 inches) in length and weighing over 200 kilograms (440 pounds).
These molluscs inhabit the tropical Indo-Pacific, and are usually found on coral reefs in lagoons and reef flats down to around 20 meters. They can live for more than 100 years.
The thick heavy shell has four or five triangular projections around the soft mantle or dorsal body wall, which is usually yellow, brown, or green and covered with iridescent blue, purple, or green spots.
Giant clams are filter feeders. There is a large inhalant siphon at the center of the mantle that draws in water and suspended food particles.
However, they receive a significant amount of their nutrition from symbiotic single-celled algae called zooxanthellae that live in the tissues of the molluscs’ mantle.
These algae photosynthesize during the day and are farmed by their hosts, rather like the zooxanthellae in corals.
You can see a giant clam in situ on a reef in this video.
Matthew Oldfield is a freelance photographer based in Bali, Indonesia, specializing in editorial and documentary images from both above and below the waves. He works primarily with charities, NGO’s, and other organizations working to conserve the environment, endangered species, and disappearing cultures.
