Tridacna gigas
Photo: B Coleman
What to look for
Two heavy, fluted shells wedged into the coral, open to show a thick mantle patterned in blue, turquoise, green and brown with rows of tiny eyes along the edge. Pass a hand’s shadow over it and the clam closes slowly: the eyes see you. The mantle colours are different on every clam, like a fingerprint.
Solar powered
Giant clams get most of their food from the algae living in the mantle, which is why they sit in the sunlit shallows with the mantle spread wide. They can live for a hundred years and, despite the stories, cannot trap a diver: the shells close far too slowly. They were nearly wiped out across Asia for the shell and meat trade, and Australia’s reef holds the biggest surviving populations.
Where to see it
- Reef dive · Outer reef Thetford ReefMax depth 5-30 m.
- Reef dive · Agincourt Reef Horse ShoeMax depth 20 m.
- Reef dive · Agincourt Reef Phil’s ReefMax depth 16 m.
- Reef dive · Agincourt Reef The PointMax depth 25 m.
- Reef dive · Agincourt Reef Three SistersMax depth 20 m.
- Reef dive · Agincourt Reef Turtle BayMax depth 22 m.
- Reef dive · Agincourt Reef West EndMax depth 15 m.
Dive with us to see it
You might also see
- AnemonefishThe clownfish of the reef, living in a sea anemone that would sting anything else. Nearly every site has a family.
- Green turtleThe turtle you’ll meet most on the reef: grazing on the shallows, resting under ledges, surfacing to breathe beside the boat.
- Titan triggerfishThe biggest triggerfish on the reef, and the one with a reputation: give a nesting female a wide berth.
