Perhaps the most dramatic of all clams is the giant clam (Tridacna gigas) – the world’s largest bivalve mollusc. They were once plentiful around the reefs but as a traditional food source they have been over-harvested and are now becoming increasingly rare. Thankfully some conservancy projects are re-seeding clams with good success.

Giant clams are an important and integral part of the reef, serving as nurseries for a host of fish and invertebrate species including damsels, gobies and tiny commensal crustaceans such as shrimp. They also act as filter feeders, sifting planktonic debris from the water for food thereby improving overall water quality.

The giant clam can grow to over four feet (1.2m) and weigh around 500 pounds (225kgs) and are estimated to be able to live one hundred years or more. Although they are filter feeders their great size is largely due to a symbiotic relationship that clams have with zooxanthellae algae which live in the clams’ mantles and provide nutrients in the form of sugars to the clam as a bi-product of photosynthesis.

Take a closer look next time you dive and you’ll see stunning patterns and brightly coloured mantles which will be unique to each clam thanks again to the symbiotic algae.