The tridacna
- Friendly Fins
- Dec 23, 2024
- 4 min read
Updated: Mar 7
The most striking shell on the coral reef
When we are snorkeling in the coral reef, it is difficult to focus our attention on one animal in particular but our gaze certainly cannot help but rest on the tridacna.
"Who exactly am I? I always hear you call me by the most disparate names like stone, serpentine "thing" or coral but in truth I am a mollusk!"
What is tridacna?
The tridacna is part of the large group of molluscs that, after crustaceans, are the animals that have developed more adaptations in the sea, diversifying and colonizing the most disparate environments. To be precise, the tridacna is a bivalve mollusc, that is, it lives inside two "valves" or shells, which it produces itself, like mussels and clams, to be clear.
How we recognize it in the coral reef:
It is typical of the coral reefs of the Indian and Pacific Oceans;
It is firmly cemented to the reef;
It looks like a “colorful wave” among the corals;
The size varies from a few cm of the youngest animals up to 1.5 m of the giant tridacna;
The shell is very strong and you can see the various external growth rings, some also have a surface rich in protuberances. (The largest specimens can weigh up to 200 kg)
The colors are super varied but all very bright and fascinating: they go from a fluorescent blue, to blue, green, pink, with darker spots or brown with lighter streaks, and on to those who have more imagination!
At the slightest movement of the water it tends to close, to protect itself.
How the tridacna lives
We said that it is a bivalve mollusc but like all bivalves it is also called lamellibranch, that is, equipped with lamellae (gills are the respiratory organs of many marine animals). What does this mean?
“My gills are comb-shaped to better filter the nutrients I find in the water!”
What we see is nothing other than the animal's mantle, that is, the outermost part in contact with the shell and which produces it.
If we pay attention when we observe it, we will surely notice two holes without tentacles on the mantle: one is used to let the flow of water in and the other to let it out, in the middle there will be precisely these gills perfectly evolved for efficient filtering of nutrients (plankton).
“I am very smart and comfortable, thanks to this special mechanism I don't need to move to eat!”
The tridacna is a very hospitable shell, as it lives in symbiosis with an alga (perhaps the most important algae of the entire coral reef): the unicellular alga zooxanthella. Well, the color of the beautiful tridacna depends on this alga, but not only that! The function of the zooxanthella is of vital importance: it produces both oxygen and organic substance through photosynthesis for our friend the tridacna, about 90% of its needs!
Friendly Fins is not trivial.
What does it ask for in return? Light and protection, this is one of the reasons why the tridacna lives in the first meters of depth, in places that are always sunny. A situation of prolonged shade would seriously compromise its life.
“And my life is very long! I can live even more than 30 years!”
The shell of the tridacna
The shell of extraordinary beauty has become its curse unfortunately, fished without control for centuries, now it is among the vulnerable marine species precisely because its number is significantly decreasing. In some countries of the world it is also eaten because its adductor muscle (i.e. the one that allows the closure of the animal's valves) is considered a delicacy. Furthermore, fishing for resale to the large aquarium industry also has its percentage of damage to this peaceful animal.
Can we do something about the tridacna?
As always, my war continues against the collection of corals and shells, alive or dead, beached or in the sea. Even if we find the empty shell of the tridacna, it must not be collected because it will return to the marine environment, crumbling and giving life to new calcium carbonate that will be reused by other animals to produce new shells.
By buying them at local stalls we obtain the same result as direct collection.
"As long as someone buys us, there will always be someone who will fish us out to sell us."
After all, we are no longer in the 1800s when we need giant clams to make holy water for churches, nor in the 1900s when we need shells as ornaments in our bathrooms.
Times are changing, Friendly Fins, let's modernize too!
I am increasingly convinced that a beautiful photograph is enough to have a beautiful memory of the holiday! If we are really willing to spend hours on a plane, to spend money and time in extraordinary places, the LEAST we can do is leave them as we find them, WITHOUT EXCEPTIONS!
Comments