Giant Clams | JONATHAN BIRD'S BLUE WORLD



Giant clams are no myth. In New England, people love clam chowder, but in the Pacific, some of the clams are as big as a suitcase! On an expedition to Micronesia, Jonathan goes in search of Giant Clams. These clams are so big that people used to think they caught people–and it almost looks like they could. It turns out that the problem is too many people eating the clams.

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Compared to those little New England clams, this tropical clam is a monster. But I heard about giant Killer clams here in the tropical Pacific that can reach 3 feet across and several hundred pounds. The real question is why do they call them Killer Clams? Do they kill people? Can they grab you by the foot? I don’t know but we’re here to find out.

I have come to the middle of the Pacific ocean to find a Giant clam, more specifically known as the Tridacna clam.

In the Marshall Islands, people have been eating Tridacna clams for thousands of years. A mature Tridacna can feed quite a few people. Except for being a bit heavy, hunting these clams isn’t very hard…it’s not like they can get away. So they have been over-harvested in most of the Pacific, and finding them these days is not an easy task.

I set out to a secret place in the Marshall Islands where there are supposed some giant clams.

Well, this is the spot so I guess now its time to go look for some killer clams!

When I hit the water, I start to search for the clam. The reef is beautiful, with healthy coral everywhere. This is a perfect place for a Tridacna. All I have to do is look around.

At least I see a Tridacna clam! It’s grown into the reef—so it’s a little hard to spot.

It responds to my hand movements. That’s because it is sensitive to light and when my hand casts a shadow on it, the clam retracts to protect itself.

This is why people thought they were dangerous. Could a clam this large actually grab my hand?

Lets find out. I put my hand into the clam and it closes—but the clam can’t actually close all the way. All my fingers are still there. So much for the killer clam.

Tridacna clams live in shallow, sunlit waters. This is no coincidence, because they are solar-powered. The clams have symbiotic algae in their tissue. The algae absorbs the energy from the sun and turns it into energy that it shares with the clam. Without the sun, and the algae to turn it into energy, the clam would die.

Clams also feed on plankton in the water. They have two openings, called siphons. The clam slurps up water through the incurrent siphon, and filters the water through a sieve, extracting the plankton. Then the water comes back out through the excurrent siphon. The giant clam can filter hundreds gallons of water every day with this method.

Unfortunately, there isn’t much plankton in clear tropical water. That’s why the clams need the algae.

These reefs would be teeming with giant clams except for the fact that they taste good—so they have been overfished.

Here on the island of Kosrae, overfishing of giant clams in the past has left the reefs depleted of these incredible animals, so the solution is a clam farm!

Kosrae is known for having one of the world’s few Tridacna clam farms. Here they raise hundreds of the clams both for food, and to release into the wild.

A dozen large tanks have clams of different sizes soaking up the tropical sun. Seawater is pumped in from the ocean. These clams make their own food from sunlight, just like plants. All they need is a circulating water supply and time to grow.

As you might expect, they don’t grow very fast.

So if a 5 pound clam takes 7 years to grow, we can only imagine how old this clam is. This hundred pound tridacna might easily be more than 50 years old. It’s three feet across! Experts say that they may live for a hundred or more years.

So the are old clams, and they’re big clams, but they’re not really killer clams. They sit on the bottom and collect sunlight. They’re about as dangerous as sponges, but that’s a story for another day.

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