Guido,

People begin to notice a relationship between acidity (the more CarbonDioxyd
in the sea, the less alcalin it is) and species vanishing.
For the moment, this relationship has not been clearly demonstrated, as the
oceans are, naturally, huge CO2 reservoirs; anthropic impacts are small,
there, but a little percent of acidity could affect the solidity  and
existence of many thin and fragile species that use dilluted CaCO3 to build
exoskeletons (Coccolithophora, Foraminifera, Pteropoda etc...): everybody
knows that CaCO3 + acid ----> porridge.

For more infos about this subject, launch a research on Scott, Doney, Woods,
Hole, Mass.
Nota bene that recent studies driven by N. Gruber (Calif) let believe that
+/-50% of the anthropic CO2 is absorbed by sea water.
Thus, it is not very surprising to see that this acidrise phenomenon seems
to begin in shallow water, and slowly attacks deeper levels, year after
year.

If all that was true, you might accentuate shell collecting, as a testimony,
because we are changing of geological layer!

Cheers

Olivier Caro

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