Dear Tom et al.,
I think the encrustations may be calcareous scale which comes out of a
calcium carbonate-saturated solution which has lost dissolved volatile acid.
Artesian water from the Floridan Aquifer, when aerated to release various
sulfurous vapors to make it potable, leaves a similar deposit as the
calcium (mostly as carbonate) and other salts fall out of solution. John's
cascade tailwater would be a perfect situation to measure a rise in pH in
the water from its upstream composition. Another effect of the waterfall
would be the cooling, which makes the water a weaker solvent for calcium salts.
Deposits of this sort are increased in proportion to the amount of exposed
surface area. Any alga which occupies hard surfaces in such a hypothetical
habitat would likely facilitate the encrustation. The microchemistry of
such surfaces, as Allen suggests, may be a factor as well.
Harry
At 07:53 AM 7/25/2004, you wrote:
>At 12:00 AM 7/25/2004, you wrote:
>>Conch-Lers,
>>
>>Seeing Paul Kanner's query about his mystery shell made me realize I might
>>be able to solve a mystery with the help of the folks on Conch-L. I have
>>some small nerites that are coated with a coralline encrustation. Of
>>course, putting that title on it does not mean I know what it is. Is it a
>>natural encrustation like a buildup of lime or is it caused by an animal
>>like a bryozoan? Big mystery. I have seen it on three or four freshwater
>>nerite species. Thanks to the generosity of Bill Frank and the Jacksonville
>>Shell Club Web Page you can see one of my shells at:
>>http://www.jaxshells.org/tome.htm
>>
>>If anyone has any ideas of what this is, I would love to hear from you.
>>Thanks,
>>
>>Thomas E. Eichhorst
>
>This may not answer Tom's question, but I collected some totally encrusted
>Vittina variegata in a steep stream -- cascade actually -- near Port Vila,
>Éfaté Is., Vanuatu, in 1995. As I recall, the entire bottom of the stream,
>made up of solid rocks, was encrusted with the same material. It wasn't
>until Glenn Duffy pointed them out, that I noticed the well-camouflaged
>Nerites. The encrustation was easy to crack off, and I kept only one
>specimen with it on. In this case, it seems to be a buildup of lime.
>
>John
>
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Harry G. Lee
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