The largest living bivalve mollusk and found on the Great Barrier Reef, the Giant Clam can grow to over 1 metre and over 200kg in weight and live for over 100 years.

Giant Clam - Tridacna (Tridacna) gigas. Viewed on a Sea Kayak trip off the Daintree Coast - Photo by Alex Pawlow

The largest ever recorded Giant Clam was found in 1817 off Sumatra and measured 137cm.

The Giant Clam has a unique circulatory system, hosting unicellular algae which adds to the food sources it filters from the surrounding water.

They reproduce by broadcasting sperm and eggs into the ocean. They are hermaphrodites so can reproduce with any nearby giant clam. Once fertalised, they can release up to 500 eggs at a time, which float around for up to 12 hours.

Once hatched, the larvae starts producing its shell and will spend the next week floating and "looking" for a suitable habitat. Once on the sea floor, it can still move with its "foot", until finally settling in one location for life.

Early growth is rapid (believed to be up to 12cm per year) but as the clam ages, growth slows.

In the early stages of growth, the clam has not yet developed its symbiotic algae, so relies entirely on filter feeding of plankton.

The Giant Clam is becoming rare in much of its wide range of habitats, but is often seen on the Great Barrier Reef, even on fringing reef, just off the coast.