This is indirectly shell-related, since so many species of mollucs
depend upon coral reefs: just thought i'd pass it on!!

http://www.newscientist.com/news/news.jsp?id=ns99993606

Coral bleaching caused by "malaria of the oceans"

        This much we know: coral bleaching is a modern epidemic that some
biologists predict will kill up to half the world's reefs this century
as climate change raises sea temperatures. What we have missed is that
some bleaching may actually be an infectious disease spread by a worm, a
"malaria of the oceans". Israeli scientists say they have studied a type
of coral whose bleaching is triggered by a bacterium, and found that
this is carried and transmitted by a coral-feeding worm. If the same is
true for other corals, scientists may be able to prevent the disease by
targeting the worm vector, just as they control malaria by targeting mosquitoes.
        Corals depend on algae inside their bodies to provide carbohydrates and
oxygen through photosynthesis. This partnership allows corals to thrive
in infertile areas of ocean, and explains why reef communities are so
rich. But when water temperature rises, the algae either die or the
corals eject them in response to the stress of the heat. Before too long
the entire reef turns white. It is unclear how well reefs later recover,
and the sharp rise in coral bleaching since the 1980s has sparked dire
predictions for their future. Most marine biologists agree that
bleaching is caused by rising sea temperatures, and the best way to stop
it is to cut carbon emissions. But that is an indirect, long-term
strategy that may not save reefs in time.
         Now there may be a more immediate remedy:  In the late 1990s, Yossi
Loya and Eugene Rosenberg led a team from Tel Aviv University that found
a bacterium that causes coral bleaching. Crucially, it turns out to be
more virulent at higher temperatures. "Coral biologists are not
microbiologists," says Rosenberg. "They saw the association of bleaching
with temperature, but they did not see the bacterium." The microbe,
named Vibrio shiloi, was responsible for bleaching the stony coral
Oculina patagonica in the Mediterranean Sea. But researchers were
mystified because the bacterium was only present in the summer. "We had
to find out what happened to it in the winter," Rosenberg explains. To
reveal its hideout, they added a fluorescent chemical tag to the water
around the coral. This tag attaches specifically to the bacterium's DNA,
and they were surprised to see where the fluorescence later showed
up. "I thought we would find it in the water, or at least in the
sediment," says Rosenberg. But the strongest glow came from the marine
fireworm, Hermodice carunculata, they will report in an upcoming issue
of Environmental Microbiology.  The researchers believe the worm
harbours the bacterium, and transmits it to the coral while feeding.

From the Great, Still-White North,
Ross m.