Effects of Pesticide Application on Cyprinidon variegatus in a Salt Marsh Ecosystem

1
Effects of Pesticide Application on Cyprinidon
variegatus in a Salt Marsh Ecosystem
INTRODUCTION
Brian Gibbins. Southampton College - SCERP
research project

• Long Island has extensive salt marsh ecosystems
  that are frequently sprayed with pesticides to
  control mosquito populations. Resmethrin and
  Methoprene are the two pesticides used.
  Resmethrin is an adulticide that kills adult
  forms of mosquitoes and is used when there is a
  public health threat, such as presence of West
  Nile Virus. Methoprene is a larvicide that
  prevents the juveniles to morph into adults by
  blocking biochemical pathways. These pesticides
  are directly sprayed onto the marshes and can
  accumulate into the ditch systems present in the
  majority of Long Island ditches. This
  accumulation of toxins may have an acute negative
  effect on the naturally occurring biota found in
  the ditches. To test the effects of these
  pesticides cages of young Cyprinidon variegatus
  (Sheepshead minnow) were placed in these ditches
  during spray events to monitor acute mortality.
  In situ gauges monitored the physical parameters
  of the ditches during the course of a six day
  experiment. Control Sites that were not sprayed
  were used as controls to test the effects the
  pesticides.

Adulticide Results
The adulticide experiments were conducted late in
the summer of 2004. The spray site where the
adulticide was applied was Johns Neck in
Mastic/Shirley surrounded by residential housing.
The control site was Havens Point in East
Moriches which is also surrounded by housing and
a boatyard with a park. The first experiment
showed little effect with more mortality at the
control site and little mortality at the spray
site. The second experiment showed drastically
different results with a sharp decrease in the
survival in the cages directly after the spraying
event. Overall, there is no clear evidence that
suggests a definite acute effect from adulticide
application, but there is also no evidence that
shows that the fish are not harmed by the
adulticide.
Larvicide Results
The first two larvicide experiments show a
decrease in survival after application that shows
a strong relationship between elevated mortality
and larvicide application
The second half of the larvicide applications
displays stark differences than that of the first
half. The second half do not show a pattern of
increased mortality with pesticide application.
Just as in the adulticide experiments half of the
experiments support acute effects and half do not.
The above graphs of the gauges in the ditches may
show the most important story of the whole
experiment. As the summer progressed, the
dissolved oxygen percent decreased, most likely
due to increased heat and light intensity. This
would create periods of extremely stressful
conditions that cold be enough to kill small,
juvenile fish without the aid of toxic
pesticides. This may also explain why the earlier
experiments show a negative effect while later
experiments in the more stressful conditions
cannot show distinct results.
Conclusion
The take home message from this work shows that
these environments are extremely stressful and
hostile that can create a serious challenge for
survival. Adding pesticides to such a stressed
area cannot improve the conditions and an
alternative method for vector control should be
explored to ease the anthropogenic stresses
introduced to such important and delicate
environments.