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Implications
Areas were classified by the percentage they contain of each
potential habitat type. Areas that were identified for zebra mussels
only -- if zebra mussels do establish themselves -- may see shifts
in the food web because of higher grazing of phytoplankton. There
may also be some risk of biofouling, or the accumulation of these
mussels, on different types of infrastructure. Where both zebra
mussels and sea lamprey are potential, there is risk of both
parasitism to fish and a decrease in food supply
for the fish since zebra mussels consume phytoplankton, and that
could have an effect on zooplankton abundance, the food source for
zooplanktivorous fish. Zebra mussels and quagga mussels together
could mean a decrease in phytoplankton abundance through filter
feeding. However, these two mussel species occupy different physical
environments in terms of depth and temperature (Nalepa, 2008). Where quagga
mussels are present in combination with zebra mussels, links have
been seen between an increase in water clarity (by filter feeding)
and an increase in phosphorus availability, resulting in “nuisance
algae” near the shore (Nalepa, 2008). Areas where all
three invasive species could be present will also likely see shifts
in the food web. Quagga mussels and zebra mussels might compete for
food, but they are often spatially segregated. The mussels
and the lamprey should not directly compete with one another, but
will both likely negatively impact fish.
Not only do the maps consider qualitatively what types of
dispersal may happen in each county, but quantitatively the
potential habitat that is available. Relative efforts and use of
resources for monitoring these species might wisely be based on
their relative amount of vulnerable habitat.
Limitations and
Improvements
While the overall intent of this analysis addresses an
important issue, there are some limitations to this analysis. In
determining the potential habitat for the species, the only two
factors considered where the ability to disperse inland in terms of
distance and the presence of a tributary. This might be improved by
considering other variables relevant for each species and specific
to each species, such as water temperature. The presence of dams in
the water may further limit dispersal (but does not entirely rule
out the potential for further transmission upstream).
Since there may be a difference in the monitoring efforts
between different states and counties, the data points used in the
analysis might reflect those biases and more accurately represent
confirmed areas of occurrence in some states or counties over
others. Further, while the data original data points were the
results of long term monitoring, there only extended until 2004, and
changes have likely occurred since then.
Restricting the analysis to the Lake Michigan Basin may have
neglected important contributing variables, such as invasive species
from the other Great Lakes.
Overall, classifying areas in terms of relative risk can
allow for efforts and resources to be partitioned in a way to
reflect the risk. However, the Lake Michigan Basin is not a unified
political entity, and the sources of motivation for community
involvement in species monitoring may be different throughout the
basin.
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