How old is the Giant Clam?

[Winton]

I am sorry your clam died, it would have been cool to have seen it before its demise.

 

[calypsonick]

Scubaroo,

It used to sit in the coral at 11-12 meters and then it was pried out and, as you can see from the top photos, a big hole was cut out of the mantle. The shell and remaining clam were left at 19 meters.

Two running theories: 1. the adductor muscle is a delicacy in some asian countries and that is what they were after. Locals would have taken all the mantle becasue they eat the whole clam here, whereas other asian countries only value the muscle (some use it in sashimi, others say it has aphrodisiac properties); 2. they went for the part that may have had a pearl, as some giant clams do produce them.

 

[Mako Mark]

That is a crying shame. I saw the same thing happen with a similar sized friend of mine in Oz a few years ago, its fate was just wanton vandalism. This is a good reason to stop divers carrying knives.

Tridacnia is a delicacy, in the pacific too, in some areas they keep a group of VERY large ones near the village that cannot be harvested, they do this for two reasons.

One is that the largest are the best reproductive stock, and these particular ones are called the Grandparents and seed the nearby reef with tastier younger ones, that can be harvested.

The second is that in times of starvation (like during hurricanes) there is a nearby emergency food source for the village.

This is a classic form of traditional, sustainable resource management, that had been lost in the indo pacific region, but fortunately, with encouragement is making a comeback.

 

[iainwilliams]

We have a popular giant clam here in East Timor that is approximately 1 meter in diameter. How old could it be?

How old? Depends on what you actually mean by old!

Clams have a linneage that dates from the late Cambrian Period (geologically) when hard parts iniially evolved and calcium carbonate and phosphates began to be used as a building material for marine shells and other critters.

The Ordovician Period which is the next youngest period from the Cambrian is when clams really took off and radiated evolving into many different families and species. The Ordovician is defined from 500 to 440 million years ago thereabouts. Therefore, your clam is quite OLD - well its linneage is!!................Iain

 

[archman]

Those are the EASY answers Ian! Now try for the evolutionary age for tridacnids, or at least the suborder it belongs in. I'm not even sure I have the answer!

 

[calypsonick]

Thanks Iain. What I was really looking for was the natural lifespan of a Tridacna gigas in order to get an idea on how old our deceased friend was. Is there any data on age:length for Tridacna?

Thanks
Nick

 

[archman]

Not being one to leave science questions unanswered, I did some quick searches. Here's the best I found.

Scientific name: Tridacna gigas

Distribution: Southern & Western Pacific and Indian Oceans

Size: up to 3 feet (0.9 m) and up to 600 pounds (270 kg)

Diet: plankton and nutrients produced by symbiotic algae

Despite their reputation as "killer clams", these colorful bivalves do not eat fish or people! The shells close relatively slowly and only for self-protection; giant clams cannot "snap shut" trapping unwary divers. Furthermore, fish and divers are far too large to be eaten by a giant clam.

The fleshy mantle tissue, which secretes the shells, is greatly expanded and fills the upper region between the shells. This mantle tissue contains large numbers of single-celled algae called zooxanthellae that produce food through photosynthesis. Using sunlight for energy, the tiny plant cells convert carbon dioxide and other raw materials into food molecules, some of which are absorbed by the clam. As long as there is lots of sunlight, the clams require no additional food. In fact, the clams on display at the Waikïkï Aquarium have never been fed anything except sunlight! Giant clams living on the reef, like other bivalves, may also obtain nutrition by filter feeding plankton.

Giant clams are molluscs, they belong to the group that includes other bivalves, like the oysters, scallops, mussels, and other clams. More distant mollusc relatives are snails, sea slugs, octopus, squid, cuttlefish and chambered nautilus.

There are seven species of giant clams found in the tropical Western Pacific and Indian Oceans. The smallest species reaches only six inches (15 cm) in length, while the largest species, Tridacna gigas, may grow to more than 3 feet (1 m) and weigh up to 660 pounds (300 kilograms).

The three Tridacna gigas on exhibit at the Waikïkï Aquarium were obtained from the Micronesian Mariculture Demonstration Center in Koror, Palau. The largest of the clams came to us in 1982; it was five years old and weighed 20 pounds (9 kg). It's now more than 20 years old and probably weighs over 125 pounds (56 kg). That makes it the largest and oldest of its species in the United States. The Waikïkï Aquarium was the first U.S. aquarium to display this huge species. Successful animal husbandry techniques developed here could mean that this clam will live another 50 years and reach a weight of more than 600 pounds (270 kg)!
A giant clam is sexually mature at five years of age and may produce either eggs or sperm. During spawning, many clams release their eggs and sperm into the seawater where fertilization takes place. The microscopic larvae drift in the currents with other plankton for about 10 days. Then they settle on the reef and attach to the bottom with threads produced by a gland in the foot. Juvenile giant clams are food for fishes, octopus, crabs and predatory snails.

However, by the time they are three to four years old the shells are about 12 inches (25-30 cm) long, too large and thick to be penetrated by most predators.

Both the mantle tissue and the large muscle that closes the shells are edible and highly prized by people throughout the Pacific and Asia. The shells are taken for decorative purposes. As a result giant clams are heavily harvested and have become rare on many Pacific reefs.

Clams, like many molluscs, can produce pearls. An irritant such as a piece of sand or a parasite is covered by layers of nacre (mother-of-pearl), a hard substance secreted by the mantle to form a smooth interior to its shell. However, most pearls of giant clams are not commercially valuable

Giant clams grow quickly and require no supplemental feeding. This makes them ideal for both commercial cultivation and subsistence farming. Commercial production may help to save the giant clams, which in some areas have been harvested to near extinction. Giant clam hatcheries produce young clams in seawater tanks or raceways and transplant them to nearshore reefs where they can be grown to marketable size. Enough clams are being produced for some to be placed back into natural reef areas.

 

[calypsonick]

Thanks archman! That estimate puts the lifespan at 70 years for the Waikiki aquarium individual. I have also seen 100 years cited.