The giant clam is the largest living bivalve mollusk. They are part of the genus Tridacna and have two shells. There are several species of “giant clams” in the genus Tridacna, but they are often mistaken for Tridacna gigas, which is the species most people mean when they say “giant clam.”
Giant Clam Nomenclature
Tridacna gigas is the name of this clam in the scientific world. The word “Tridacna” comes from the Greek words “tridaknos,” which means “oyster,” and “gigas,” which means “giant.” It is a member of the family Cardiidae and the class Bivalvia. This clam comes in 100 different kinds.
Giant Clam Appearance
Their thick, heavy shells protect the soft mantle inside these clams with fluted edges. Moreover, its mantle has patterns of brown, blue, green, yellow, purple, and green with iridescent blue. Furthermore, the color of this clam’s shell comes from the algae it stores in its body. The pale spots on an adult clam’s shell are called “windows.” Moreover, the length of these clams is between 4 and 4.5 feet.
They are about 500 pounds each. If you put 3 bowling pins next to each other, that’s how long a 4-foot giant clam is. A giant clam that weighs 500 pounds is the same as half a horse. Thus, the record for the heaviest giant clam is 550 pounds.
The southern giant clam is another type of this animal. Its scientific name is Tridacna derasa. Even though it looks like the Tridacna gigas, the southern giant clam is only about 2 feet long.
The size and thickness of an adult giant clam’s shell make it a good defense against most predators. Moreover, this clam can also close its shell almost all the way to protect itself. So, an adult clam can’t close its giant clam shell by snapping it shut. The clam sticks to a reef and stays there for the rest of its life.
Diet: What Do Giant Clams Eat?
These clams eat everything. But they can’t hunt for food because they are stuck in a coral reef. The food comes to them, which is good news. These mollusks have a siphon that lets them catch small animals that float by. This system for siphoning is like the filtering system in a backyard pool.
Who or what eats big clams? You might think that this clam’s size would keep all dangers away. But there are some things that eat this mollusk. The meat of the clam is eaten by reef fish, eels, and starfish. People also get meat from these clams to eat.
What do these big clams eat? The phytoplankton and zooplankton that these clams eat are both plants and animals. These clams have a siphoning system that lets them take in water and small bits of food.
Also, the clam gets sugar and protein from the billions of tiny pieces of algae that are stored in its tissue. Thus, this is what’s known as a relationship where both sides benefit. Moreover, the algae are safe when they live in the clam’s body tissue, and the clam gets the nutrients it needs in return.
During the day, these clams open their shells to let light in through the holes, or windows, in their mantles. The algae get their food through a process called photosynthesis.
Habitat: Where Do Giant Clams Live?
These clams live in places where the water is warm. They live in the South Pacific and Indian Oceans, to be exact. They live near Australia’s northern coast, the Nicobar Islands, and Fiji. Moreover, many of these clams live in the Great Barrier Reef near Australia. They live in shallow sandy areas of lagoons and on reef flats.
Most of the time, they are found about 65 feet down. 65 feet is not a very deep depth in the ocean. These clams can get filtered sunlight because they live in shallow water.
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Giant Clam Predators
The meat of these clams is eaten by eels, reef fish, and starfish. When one of these animals eats a giant clam, it doesn’t kill it. But it does hurt people.
People are also a danger to this clam. Furthermore, people get meat and shells from these clams. In particular, the adductor muscle of a giant clam is thought to be one of the best parts of this sea creature to eat. So, the Japanese, the French, and people all over southeast Asia love to eat these clams.
Fish, octopuses, and crabs eat the young of these clams. These larvae are so small that one big fish could eat thousands of them. The main reason a giant clam makes so many eggs is because of this. It makes it more likely that some of them will grow up.
These clams are also in danger from dirty water. Pollution can slow down the rate at which these sea creatures have babies. The official status of these clams is that they are Vulnerable.
Giant Clam Reproduction
There are both sperm and eggs in each giant clam. They have babies by putting both sperm and eggs out into the water. One giant clam can lay up to 500 million eggs all at once. The sperm from another giant clam is what makes the eggs grow. We call this “broadcast spawning.”
When the eggs are fertilized, the larvae come out. Giant clam larvae swim around in the water, looking for plankton and other tiny food particles until they are big enough to settle near or on a coral reef.
A giant clam goes through many stages as it grows. It begins as an egg, which then hatches into a larva. After that, it becomes a veliger, then a pediveliger, then a juvenile, and finally an adult. Giant clams take years to grow to their full size and weight, but they can live up to 100 years. So, it has a lot of time to become a 4-foot-tall, 500-pound adult.
Giant Clam IUCN Status
According to the IUCN Red List of Threatened Species, the number of these clams is not clear. It is in danger because people kill it for its meat and shell. This sea creature is also in danger from water pollution. This clam is a Vulnerable species in terms of conservation.
What Does A Giant Clam Look Like?
The edges of a giant clam’s shell are curved, and its shell is thick and heavy. Inside its shell, the soft tissue, called the mantle, has a pattern and a mix of colors like yellow, green, iridescent blue, and purple. The mantle of a giant clam is like a person’s fingerprints. No two mantles look the same.
The clear spots on a giant clam’s shell are called windows. The algae that live inside the clam’s tissue can reach the light through these windows. For algae to make food, they need to take in light.
There are also two siphons in the mantle of this clam. One siphon takes in water, plankton, and zooplankton simultaneously. The other one lets water out.
Are Giant Clams Dangerous?
No. A story that has been around for hundreds of years says that giant clams can grab divers and eat them. This is why some people call them “maneaters.” But this is just a story that movies and fantasy books have spread.
Is Giant Clam Edible?
People all over the Pacific and Asia love to eat both the mantle tissue and the big muscle that closes the shells of giant clams. People take the shells to use as decorations.
Do Giant Clams Still Exist?
Tridacna gigas are hard to find on coral reefs because people overharvest them. But giant clam aquaculture has become a good alternative to getting them from the wild. The Endangered Species Act protects giant clams from killing.
How Big Can A Giant Clam Get?
The giant clam is one of the biggest mollusks. There are different kinds of giant clams; the biggest ones can be four feet across and weigh more than 600 pounds. Giant clams have two thick, bony shells that are joined by a flexible ligament hinge. This is true for all species.
Do Giant Clams Have Pearls?
The gigas giant clam, which is the largest species, is one of the biggest clams in the world. But even though giant clams have a bad reputation for eating people and being sea monsters, they are actually gentle giants that can make beautiful, rare giant clam pearl.
Parvaiz Yousuf is a senior SEO writer and editor with an experience of over 6 years, who also doubles up as a researcher. With an MSc zoology degree under his belt and possessing complete Search Engine Optimization (SEO) knowledge, he works as a science journalist for a US-based website and Asian Scientist (A Singapore-based magazine). He also works as Director of Wetland Research Centre, Wildlife Conservation Fund YPJK since 2018. Besides, he has several publications to his name on cancer biology and biochemistry in some reputed journals such as Nature & International Journal of Molecular Sciences, & magazines such as Science Reporter, BUCEROS BNHS, and has an abiding interest in ornithology. He also worked as a Research Associate for JK Policy Institute.