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Giant Clam: The Life and Trials of the Ancient Mollusk

Giant Clam: The Life and Trials of the Ancient Mollusk

Written by Leisure Pro Staff
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Published on June 23, 2014
giant clam

Giant clams are the largest species of clam on Earth. Once rumored to be a man eater, there are no actual cases of a giant clamshell snapping shut on an unsuspecting diver, but they are omnivores, eating both plants and small animals. Inhabitants of the great stony coral reefs of Indonesia and the South Pacific, they fasten to one spot and stay there for life. The multi-colored flesh within their shells is much like a fingerprint to us humans: no two patterns are ever the same.

The lifespan of a giant clam

Life in the case of these monster mollusks can span a period of a century or more, as long as they’re in warm, clear, and fairly shallow saltwater. Water quality is very important, since the clams both house and feed on algae that require photosynthesis to survive. During the day, their giant, ruffled maws gape open, revealing the fleshy animal inside. They bask in the filtered sun, siphoning water and catching plankton as it drifts by. Not a bad way to spend a 100-year lifespan!

giant clam shell underwater
Photo by Vandan Jhaveri on Unsplash

How a giant clam reproduces

Giant clams are hermaphrodites, but they do not reproduce asexually. Rather, they release sperm and eggs into the water at mating time, which mixes together with the sperm and eggs of other giant clams to produce larva that will eventually settle on the seabed or reef and begin a new life. They can grow to be 4-6 feet in length and top out at around 500 lbs.

Diet: What does a giant clam eat?

Just like some coral species, giant clams share a symbiotic relationship with millions of single cell dinoflagellate algae called ‘zooxanthellae’. They consume the sugars and proteins produced by the billions of algae that live in their tissues; in exchange, they offer the algae a safe home and regular access to sunlight for photosynthesis, basking by day below the water’s surface with their fluted shells open and their multi-colored mantles exposed. They also get nutrients by siphoning up and filter feeding on passing plankton.

Predators

Despite their gargantuan size, they do have a few marine predators like starfish, snails, reef fish and eels who take advantage of the sessile nature of the giant clam and settle in for a bite.

Their most dangerous predator is actually the human, who discovered that the fleshy adductor muscle that opens and closes the shell made for a delectable delicacy. In fact, over-harvesting of giant clams has reduced their population so drastically in some regions, such as Fiji, that they are considered to be endangered locally.

giant clam
Photo by NOAA on Unsplash

Threats

Unfortunately, the Tridacna gigas (giant clam) is one of the most endangered clam species with it’s numbers diminishing at an alarming rate. The giant clam is a delicacy in Japan, France and some other South-East Asian and Pacific countries.

But, the main reason for this species’ declining numbers are mussel-catching vessels that uproot these uncharacteristically large creatures. The shells are even sold in the Black Market as decorative ornaments and in some cultures like the Chinese, the adductor muscle, believed to have aphrodisiac powers, is sold for large sums of money.

So the next time you consider buying one of these giant clam shells as garden decoration, as footbaths, sinks, or foodbowls, remember that this ecosystem that supports thousands and thousands of species and life forms.

Giant clam: A misunderstood species

This huge shellfish, has often been misunderstood in history and were once labeled the killer clam or man-eating clam! However, the clam is not aggressive at all and while it is certainly capable of gripping a person, the shell’s closing action is too slowly to pose a serious threat. So all those stories of divers or fisher folk drowning because of giant clams latching on to their arms with malicious intents were all discredited to be false.

The presence of Giant Clams are actually an indication of a healthy coral reef. These creatures are highly sensitive to changes in the water acidity and temperature and perish where conditions are less than perfect. They also play a very important role in the reef as they act as nurseries for a host of fish and invertebrates as well as shrimp. Clam shells even provide the perfect substrates for attachment for several species of sponges, coral and algae which promote the development of the reef.

Leisure Pro Staff

Leisure Pro Staff

Marketing Director for LeisurePro