I received the following from another list I am on (water issues).  It
doesn't deal with shells directly but it is a critical report on the
environment of seashells.

Tom Eichhorst in New Mexico, USA

Soaring ocean temperatures in the Caribbean have caused the first mass
die-off of coral in the region for 3,000 years.
Scientists suspect that the record temperature of 31.5 deg Celsius, recorded
in 1998 off Belize, was the result of global warming and the El Nino climate
phenomenon.
[snip]
"There is growing concern that global climate change is degrading coral reef
ecosystems, with coral mortality increasing as a result of bleaching and
emergent diseases: our results from Belize appear to justify this concern,"
said Richard Aronson of the Dauphin Island Sea Laboratory in Alabama, US.

The Belize barrier reef is the largest in the Northern Hemisphere.
[snip]
The researchers then used radiocarbon dating on 12 coral cores to determine
historical events on the reefs. This showed no similar bleaching had
happened for more than 3,000 years.

The research is published in the journal Nature.
[end extract]

Full article at:
http://news.bbc.co.uk/hi/english/sci/tech/newsid_735000/735941.stm