OXFORD, Mississippi, June
10, 2005 (ENS): A decline in the abundance of freshwater
mussels about 1,000 years ago across what is now the southeastern
United States may have been caused by the cultivation of maize,
or corn, by Native Americans, according to new research by scientists
with the U.S. Forest Service.
In the April 2005 issue of "Conservation Biology," Wendell
Haag and Mel Warren, who work at the Forest Service's Southern Research
Station unit in Oxford, report results from a study of archaeological
data from 27 prehistoric sites in the southeastern United States.
Of 297 freshwater mussel species found in the United States, 269
species are found in the Southeast.
“We can tie declines of specific mussel populations to the
construction of dams, stream channelization, or pollution from a
specific source,” says Haag, “but the worldwide patterns
of decline in these animals implies that larger-scale disturbances
such as sedimentation and nonpoint-source pollution may have an
Worldwide, freshwater mussels have proven to be susceptible to
human disturbance, and they are the most endangered group of organisms
in North America, say Haag and Warren.
Among freshwater mussels, members of the genus Epioblasma, known
as riffleshells, are the most endangered. Epioblasma consists of
20 species and eight subspecies; at least 13 of these species and
four subspecies are presumed extinct. Of those remaining, the snuffbox
mussel, Epioblasma triquetra, is the only species not listed on
the federal endangered list.
“Human population in the Southeast began to increase steadily
about 5,000 years ago,” says Warren. “With increasing
population came land disturbance from agriculture. This intensified
about 1,000 years ago, with the beginning of large-scale maize cultivation.
No one has really tried to look at how this change in land use impacted
water quality and aquatic organisms such as freshwater mussels.”
Working with Evan Peacock from the Cobb Institute of Archaeology
at Mississippi State University , Warren and Haag used survey data
from prehistoric shell middens - refuse heaps of shells discarded
after eating - to examine differences in the abundance of Epioblasma
species before and after maize cultivation started in the Southeast.
They compiled data from both published and unpublished archaeological
reports from 27 different sites along 12 rivers in the Southeast.
“As far as we can tell, Native Americans harvested mussels
without preference for species,” says Haag. “Shell middens
provide us with a way to establish the range of freshwater mussel
species before human impacts, and to chart changes in relative abundance
as impacts increased.”
The researchers found that the relative abundance of riffleshell
mussels in the rivers they studied declined gradually during the
period between 5,000 and 1,000 years ago and the decline accelerated
during the period between 1,000 and 500 years ago, when thousands
of acres of land were cleared for farming.
“We know that freshwater mussels are very sensitive to stream
alterations,” says Warren. “Although we cannot entirely
rule out the influence of long-term changes in climate, the dramatic
changes in land use in this period provide a compelling explanation
for the changes in mussel abundance we found.”
Today, none of the riffleshell species the researchers found in
ancient middens survive at the study sites, where they were gathered
by Native Americans over the millennia before European settlement.
Most are extinct as a result of modern land disturbances.
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