Media Contact: Lisa Young
251/861-7509
Habitat modifications are among mankind’s
most pervasive alterations of our nation's estuarine ecosystems. When
such modifications are extensive, as is the case for the Mobile Bay
Causeway, they can alter patterns of natural hydrography. Among the
possible consequences of the Causeway is the reduction of water exchange
between the fresh water in the lower reaches of Mobile-Tensaw Delta, and
the saltier waters of the Gulf of Mexico. If true, this barrier may
have created persistent low salinity conditions that local
conservationists believe have provided refuge for an exotic species of
submerged aquatic vegetation, the Eurasian Milfoil (Myriophyllum
spicatum) to survive in during periods when salinity is high
throughout this estuary.
When salinity is low, milfoil fragments from these freshwater refuges
end up in nearby estuarine grassbeds, where they subsequently outgrow
and competitively displace native submerged grasses.
To test these hypotheses, Dr. John Valentine and Marine Technician Susan
Sklenar, both of the Dauphin Island Sea Lab (DISL) in Alabama, are
currently comparing the results of salinity tolerance experiments they
have conducted using milfoil at the DISL with two years of field data
which document salinity patterns within the upper reaches of Mobile Bay.
The preliminary results of these experiments suggest that only the most
extreme salinities, those observed during hurricane landfalls in the
northern Gulf of Mexico, are lethal to milfoil.
“Right after Hurricane Katrina, we noticed that milfoil was not as
abundant in those places where it used to be plentiful,” recounts Dr.
Valentine. “Whether it was the turbidity from the storm or the salinity
from waters crashing over the MBC, we’re hoping these experiments will
be able to help determine the cause.”
In the coming year, Dr. Valentine and his colleagues will be conducting
additional field experiments to determine if in fact milfoil will
outcompete native grasses for habitat within this estuary. It is hoped
that these experiments, when completed, will allow DISL to make
data-based recommendations for habitat restoration later next year.
Dr. John Valentine – jvalentine@disl.org
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