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Snail Science:
Old shells, isotopes, and salty water
Following the trail of
snails through the springs and seeps of the Great Basin is a means
to an end for Dr. Saxon Sharpe, a paleoecologist in the Desert Research
Institute’s Division of Earth and Ecosystem Sciences. Sharpe’s
purpose is clear: she wants to know what ancient snail shells remaining
from the region’s prehistory can reveal about past—and
perhaps future—climate and the conditions that supported the
snails’ many tiny, unique, and isolated habitats.
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| Where the nails are.
Dr. Saxon Sharpe collects snail shells for clues to the environment
thousands or millions of years ago. - Photo by Kelly Conrad |
Sharpe works with shells
as small as the tiny balls of medicine packed inside 24hour cold
relief capsules—in fact, that’s how she stores them!
Others are as large as the familiar restaurant variety, and there
are many sizes in between. Radiocarbon dating is used to determine
the age of the shells, or of the material in the sediment in which
the snails’ shells were found. After preparing her shell specimens,
Sharpe sends them to a laboratory for analyses of the isotopic ratios
of oxygen and deuterium contained in the shells.
“Snail shells can
be considered waste products excreted by the snails that eventually
grow into their protective armor,” she says. “Included
in that waste are fixed stable isotope ratios from the water the
snails lived in that help to identify changes in the hydrology that
occurred during the snails’ lifetime.
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| Snails' details are important.
Examined by microscope, Sharpe
identifies snails shells for further preparation before sending
samples for stable isotoep analysis. - Photo by John Doherty |
“Was there a steady
flow of water through the snails’ habitat, or did the water
flow in and stay there to evaporate? This approach gives us specific
data about how each spring or seep was affected by varying precipitation,
groundwater flow, and climate.”
Another approach of Sharpe’s
research, and one that is brand new in the field of malacology—the
branch of zoology dealing with mollusks—is to understand how
the relative proportion of salts—specifically calcium and
carbonate—in water affects the distribution of different snail
species.
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| A spoonful of clues to
past and present environments. These
are someof the larger varieties of snails that Sharpe analyzes
for clues to ancient climates and the unique mix of salts that
make up suitable habitats for individual species. Photo
by John Doherty |
“For example,”
Sharpe says, “the occurrence of an individual springsnail
species may be tied to a particular ‘type’ of water.
This water ‘type’ is based on something we, as humans,
cannot see, taste, or feel: the percentage of calcium or carbonate.
The ‘type’ of water a snail inhabits may turn out to
be as important as water temperature or food sources.”
And why is it important
to know so much about snails? Because, Sharpe points out, “once
we understand what’s important to a particular species, we
can begin to figure out how to preserve the essential aspects of
individual habitats and preserve biodiversity for the future.”
–John Doherty
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