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SPRINGFIELD — It may not be a case for The X Files, but just
how Daphnia lumholtzi, an exotic species of zooplankton, came to
inhabit Bull Shoals Lake is an alien invasion that eludes scientific
explanation. First discovered in Texas in 1990, D. lumholtzi has
spread to over 100 reservoirs and lakes throughout North America and
continues to expand its range rapidly. Tina Tamme, a biology graduate
student at Missouri State University, is conducting experiments
that may provide insight into the mystery that remains unsolved after more
than a decade.
Her research is taking place at the Bull Shoals Field
Station, a center for research and education in an outdoor setting. The
Field Station is located on the western end of Bull Shoals Lake and adjacent
to the 6,000-acre Drury-Mincy Conservation Area. Missouri State faculty, graduate
students and visiting scientists conduct research there throughout the year.
D. lumholtzi is native to tropical and subtropical
lakes in east Africa, east Australia and the subcontinent of India. Although
no one is certain how it was first introduced to the U.S., many suspect that
it was transported with shipments of Nile Perch from Lake Victoria in
Africa. Nile perch were introduced to Texas as early as 1983.
D. lumholtzi is distinguished from native species of
zooplankton (a form of plankton, microscopic organisms which float or drift
with water currents) by its much longer helmet and tailspine. Current
research suggests that the invasive organisms do not displace native species
of zooplankton and is not a threat to the ecosystem. However, it may be too
soon to detect all of its ecological impacts.
Bull Shoals Lake is one of the many reservoirs in the
Southern and Midwestern United States invaded by the new species. However,
its surrounding ponds remain uninhabited by D. lumholtzi. Tamme's
research focuses on discovering why the foreign zooplankton have not spread
to these ponds.
Tamme uses 20 child-size pools to simulate the ponds'
environments. She manipulates factors in the pools to carry out two
different experiments. The first varies the amounts of algae, a food source,
and introduces predators, such as salamander larvae, into the environment.
The second exposes the exotic zooplankton to native species from a local
pond. By comparing the results of these experiments with actual measurements
from Field Station ponds, Tamme hopes to determine whether pond conditions
are a suitable habitat for D. lumholtzi.
"If I determine that D. lumholtzi is not able to
survive in the pond environment, dispersal by natural means may be
occurring, but the organism may not be able to tolerate the environment once
it gets there," said Tamme.
However, if her study reveals that D. lumholtzi could
survive in the ponds surrounding Bull Shoals Lake, the question as to why
the species has not yet inhabited the ponds remains.
One possible answer is human intervention. The close
proximity of affected reservoirs in Missouri to the site of the species's
first appearance in Texas leads many scientists to theorize that human
intervention is causing the wide dispersal of the exotic zooplankton. Their
preferred mode of transport may be "hitching rides" on recreational boats.
"It is not likely that a boat visiting a lake will also
visit a pond," Tamme noted. "If D. lumholtzi is able to thrive in the
various conditions I am subjecting it to in my experiments, human dispersal
may be a major contributing factor as to why they have not dispersed to the
pond environment."
Tamme graduated cum laude from Missouri State in 1999 with a bachelor
of science degree in biology and a minor in professional education. She will
finish her study and begin writing her graduate thesis in December. After
graduation in May 2002, she plans to continue working as a researcher in
freshwater biology.
For more information about Missouri State's Bull Shoals Field Station,
visit www.bullshoals.missouristate.edu.
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Bull
Shoals Field Station
