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 equal impact.”
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
“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They compiled data from both published and unpublished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.
Copyright Environment News Service (ENS) 2005. All