Range: Indo-Pacific marine waters Habitat: Coral reefs and shallow waters Size: 0.5-4.5 feet in length (15.24cm-1.37m) long Diet: Plankton, detritus, and more Threats: Crabs, parrotfish, wrasses, rays, and turtles Life span: One hundred years or more

Transcript:

Today on Animal Fact Files, we're talking about giant clams. Smooch the sub button to stay up to date with new episodes. We say smooch because these clams are often referred to as blue-lipped clams, and I’m guessing you can see why. Those “lips” are what’s called the clam’s mantle. Inside this mantle, giant clams house microscopic symbionts who not only contribute to the giant clams’ colorful displays but also their gargantuan proportions.

The largest species of giant clams, and in fact the largest bivalves in the world, are the species most often referred to as the giant clam, but, technically, there are about a dozen giant clam species. These guys stand out from other clam species because they stick the hinge of their shell into substrate while most other clam species dig in the opposite way.

The biggest giant clams may have shells more than four and a half feet in length (1.37 meters), but smaller species like the boring giant clam may only reach just under half a foot (15.24 centimeters) in length. As a disclaimer, the name ‘boring giant clam’ doesn’t relate to how fun they are to be around and actually pertains to their behavior of literally digging into the reef or rocks around them. That being said, giant clams tend to live in coral reef communities as well as shallow coastal waters of the Indian and Pacific oceans.

The zooxanthellae living within their mantle require sunlight for photosynthesis, so giant clams have to ensure they’re positioned in waters that give these symbionts as much access to sunlight as possible. This relationship is mutual. While giant clams are filter feeders consuming plankton, detritus, and any other edible particles floating by, they are also able to consume the excess sugars and proteins produced through photosynthesis performed by the zooxanthellae; in turn, the giant clam offers a safe place for the zooxanthellae to live. Supposedly there are myths that these giants can eat humans, but that’s dumb.

It’s thought that giant clams may be able to live for more than 100 years, though actual reports for this still need developing. Depending on the species, giant clams may start reproducing around four years of age. This likely won’t come as a surprise to long time viewers of this show, but giant clams breed via spawning. They’re a little different from most spawning species because they don’t release all the bits at the same time, but apparently this strategy works for them because one researcher has been quoted saying they’re the “pinnacle of fecundity in the animal kingdom”.

Different species spawn at different times and separate factors, such as tide, temperature, and even the lunar cycle may influence when spawning takes place. Swimming larvae will hatch from the fertilized eggs within twenty four hours and within two weeks they’ll have settled to the ocean floor to begin life as a tiny giant clam. It’s during this larval phase that giant clams consume the zooxanthellae that will grow with them for the rest of their lives. As they grow, their chances of being eaten by animals other than humans lessens, but throughout their lifetime giant clams may be prey for crabs, fish such as parrotfish, wrasses, and even rays, as well as turtles.

Why giant clams look so brilliantly bright has to do with many factors. The zooxanthellae play a part in coloration but so do cells called iridocytes which sort of act like sunscreen for the giant clams’ mantle. I mean, if you think about it, they spend a lot of time in the sun; even they have to watch out for sunburn!

For more facts on giant clams, check out the links in the description. Give a thumbs up for awesome animals, and thank you for watching Animal Fact Files.