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Clams & Giant Clams

Giant clams are really a sight to see in the Whitsundays. These amazing and formidable animals lay all over the ocean floor, decorating corners and crevices everywhere. You will see little clams wedged in cracks in the coral that they slowly grow into, all the way to giant clams sitting on the reefs floor or squeezed between rocks. With a hard outer shell and a brightly coloured flesh inside, they are hard to miss and an amazing site to see.

Giant clams are the largest living bivalve mollusc. They can weigh more than 227 kilograms, measure as much as 1.2 metres across, and have an average lifespan in the wild of 100 years or more.

The mantle tissues (the colourful 'lips' or fleshly inside) act as a habitat for zooxanthellaethe, the single-celled dinoflagellate algae from which it gets its nutrition. By day, the clam spreads out its mantle tissue so that the algae receive the sunlight they need to photosynthesize, which in turn gives the clam it’s nutrients.

While these magnificent molluscs are a favourite of today’s snorkellers and divers, historically, they have been very misunderstood, and even feared. Known in the past as a ‘killer clam’ or a ‘man-eating clam,’ it was believed that these giants would consume people. Reputable scientific and technical manuals made these claims, with versions of the U.S. Navy Diving Manual reportedly demonstrating how to release oneself from a giant clam by severing the clam’s adductor muscles that they use to close their shell.

Today the giant clam is not considered to be a threat to divers and snorkellers as it is neither aggressive nor particularly dangerous. While it is certainly theoretically capable of holding one in its grip, in reality the shell's closing action is a defensive response, not an aggressive one, and the process of closing the shell valves is far too slow to pose a serious threat. In other words, the clam is incapable of suddenly snapping shut on a person's arm or leg and drowning them, as it was previously believed. The best thing to do when you come across one of these beauties is stop and admire them, and to keep all limbs and fingers far away.

Lucky for us here on the Great Barrier Reef they are a protected species. However, some islands throughout the Pacific they are harvested for food. If you do some across one, you’ll see the bright flecks of colour within its flesh and their amazing and beautiful pattern that is unique to each individual clam.