Species Fact Profile: Giant Clam (Tridacna gigas)

                                                           Giant Clam

                                           Tridacna gigas (Linnaeus, 1758)

Range:  Indo-Pacific Ocean

Habitat: Coral Reef, up to 20 meters deep

Diet: Plankton, Photogenic Output of Symbiotic Algae

Social Grouping: Asocial

Reproduction: Hermaphroditic, each clam producing eggs and sperm.  Cannot self-fertilize.  Spawning season varies across range, broadcast eggs and sperm in the water.  Fertilized eggs float in the sea until larva hatches in about 12 hours.  At roughly one week, the clam settles on the seafloor, though at this stage it can move with a "foot."  Mature at about 15 centimeters in length

Lifespan: 100 Years

      Conservation Status: IUCN Critically Endangered CITES Appendix II

• Largest living bivalve, with a maximum shell size of over 1.2 meters and weighing over 200 kilograms (record weight over 330 kilograms).  Shell consists of two thick, slightly elongated valves joined by a hinge; the top valve has flattish-folds which interlock on the margin with those on the lower valve, protecting the soft clam muscle inside (though unlike other giant clams, the shell cannot close completely)
• Valve is gray-white, sometimes with pink, orange, or yellow tint, while inside is the soft body wall of the mantle
• Symbiotic relationship with photosynthetic algae, which grow in the mantle tissue.  This algae protects that clam from excessive UV radiation while also providing nutrients; the clam in turn provides a safe place for the algae to grow
• Clams of the genus can produce large, white pearls
• Genus name comes from the Greek for "three-bites," Ancient Romans claimed that these clams were big enough to require three bites to consume.  Species name refers to the giant sizes
• Collection from the wild both for meat, for the aquarium trade, and for their shells, used as decoration.  In Chinese Traditional Medicine, the muscle is believed to have aphrodisiac properties.  May be increasingly vulnerable to loss of both coral reef habitat and photosynthetic algae due to climate change (ocean warming, photosynthesis.  Programs in place to develop sustainable aquaculture, and there have been restocking efforts in the Philippines

Zookeeper's Diary: I'll admit, when I saw my first Tridacna, labeled simply as "giant clams," in a zoo, I was a little... underwhelmed.  Not being especially knowledgeable about invertebrates, I didn't know that there were many species of giant clams, the ones I saw being the smallest of them.  I've seen museum species of the shells of  T. gigas, which can stretch over a meter across and produce some tremendous pearls.  These shells dwarfed the actual specimens I later saw.  Contrary to legend, giant clams pose little safety risk to humans, and they cannot slam their shells shut, trapping and drowning divers

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