Do light needs of Tridacnids increase with age?

[Rovert]

I was just reading an interesting article by one of our members about his theory on Elegance corals, and this statement caught my eye:

We know that T. clams require more light as they grow due to the skin on their mantels becoming thicker with size.

Is this true? Do the Tridacnids require more light as they get older? I thought the inverse was true, that they required more light when younger because the mantle was not as developed, meaning there was less surface area for zooxanthellae, therefore more light was necessary than an older clam with a larger mantle.

[jsl6v8]

I know young clams tend to need more in the way of food supplements than larger ones and the larger ones live pretty much off light, other than that.

[Rovert]

Yeah, that was always my understanding about young clams, too. But the suggestion that older clams need more light because their mantles are thicker is a new claim to me. That's why I'm curious.

[jsl6v8]

seems sort of logical if they aren't eating as much phytoplankton but does it mean more light than they were previously getting or just they use the light more. In other words would I need to upgrade my lighting, or leave my MH on longer, as the clam gets larger or will it just be using the light more efficiently. Also as the clam gets larger they will be using more light as they have a larger surface area for the light to hit. Sorry if I'm rambling.

[jmaneyapanda]

This is not how it works. For simplicity's sake, you can say zooxanthellae live within the mantle, not necessarily underneath it. So as the clam grows, and the mantle also grows, light needs to penetrate no deeper than before. Some species of clam start life attached to the reef structure (rocks) by byssal threads, and when they get older, and larger, can release, and rely on their weight to simply hold them in place on the sea floor. So this species will actuallt likely recieve less light as it ages.

[Rovert]

Originally posted by jmaneyapanda
This is not how it works... as the clam grows, and the mantle also grows, light needs to penetrate no deeper than before.

Yep, that was pretty much my understanding of it. Then you believe this guy's clam about clams needing more light as they age is incorrect? If so, it makes me wonder about the rest of his hypothesis related to elegance corals.

[jmaneyapanda]

Based on my experience, I would say he is incorrect. At the very least, his logic is flawed. The "thicker skin blocking transmission of light throiugh it" theory shows a misunderstanding of clam physiology. I have had clams for about 5 years, and they are growing well under the same lighting. Any many others have had clams for much longer than me.
In nature, clams dont migrate towrads the surface as they get older. In certain species, they may even go deeper as they get larger, and more rely on their weight to anchor them in the sand bed.

[Rovert]

Ok, I'm with 'ya. Just wanted another opinion or two, just for $hits and giggles.

[critterkeeper]

Two things:

Actually, yes, as a clam gets older its mantle gets thicker and some of the zooxanthellae in the lower parts are shaded to some degree by those in the upper part. Thus, the shaded ones make less "food" for a clam.

However, a clam's respiratory rate also drops a great deal as they get older and older, thus they need less and less food relative to their size (mass). Just like old people...


Apparently this "system" works pretty well...

[jsl6v8]

I'll have you know my grandpa eats like a pig and drinks like an irishman.