DS>Now that you raise the point I cna't recall seeing any references to
DS>growth on turtles either.  If someone knows the answer I'd appreciate it
DS>if you pass that on to me otherwise I think I'll do a little digging of
DS>my own.
I have not had much experience with turtles but I have noticed that the
shells on live turtles I have seen have a rough surface and not the
smooth surface you see on shells on display.
My theory is based on the fact that the carapace is an adaption of the
reptilian scale.
Reptiles shed their skins periodically when the new skin underneath is
grown to the proper stage. They shed their scales with their skins.
Now comes the guesswork.  When turles shed their skins, the area of the
carapace is not shed but adheres to the new skin. The result is that the
shell is built up on the inside in distinct but strongly adhering
layers.
I believe that the outer layer gradually deteriorates and eventually
comes away.  There are possibly two mechanisms at work and the relative
importance of each would vary between species. Firstly, there is the
deterioration of the outer layer itself. Then there is the deterioration
of the adhesive between layers.
When the layer is more resistant to deterioration than the adhesive then
the outer layer would come away at one time and show a clean shell. In
the reverse case the layer would come away a small piece at a time and
in the extreme case would not show a smooth shell at any time.
Back to the original question, barnacles and such would not be able to
take hold for long because they would be shed with the layer they were
attached to.
There is a lot guessing there so feel welcome to shoot the theory down
in flames and we will all learn something.
Regards
Stephen
Popondetta, PNG.
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