As a member of the ecology team for the Potomac Environmental Research and Education Center’s (PEREC) summer OSCAR team project, my research goal is to investigate the predator-prey dynamics between fish and macroinvertebrates in two freshwater tidal Potomac River tributaries, Gunston Cove and Hunting Creek. This means, I examine the stomach content of 15 fish species known to inhabit both embayments in order to construct a food web for each location.
variations in aquatic habitat types within the embayments (i.e., vegetated and
non-vegetated), I use three different methods to collect my fish samples: fyke
nets, seine nets, and otter trawls.
A fyke net is a
passive collection technique in which fish are guided into a funnel shaped net
by three leads, or guide nets. Once fish enter the funnel through narrow
openings, they are unable to return to the outside of the net. The funnels on
the fyke net are comprised of subsequently narrower openings that make exiting
the net difficult for many fish. This method is implemented in heavily
vegetated habitats where the submerged aquatic vegetation is so dense it is
impossible to actively pull other types of net through.
method, seine nets, are an active collection technique in which two people extend
a long net perpendicular to the shore and then drag it parallel to the
shore for approximately 100 feet. This targets fish along the shoreline and can
be used in vegetated and non-vegetated habitat. However, seine nets become very
difficult or even impossible to use effectively once the vegetation reaches a
method, otter trawls, are another active collection technique in which a
weighted net is dropped off the back of the boat and dragged at a constant
speed for 5 minutes. Like the seine net, this method can be used in vegetated
habitats to an extent. If there is too much vegetation, the trawl will become
clogged or too heavy and will have to be reset, so it is best used in open
Once my fish
samples are collected, I take them back to the lab to remove their stomachs for
examination. I then sort the contents of their stomach into groups based on the
lowest possible taxonomic level, which can be challenging if the organisms in
the stomach have already begun to digest.
While there are
published studies focused on the diet of many of the fish species I am studying
this summer, none of the studies focus on populations in these specific
tributaries of the Potomac River. The species found in these systems are
unique, in a way, due to their close relationship with wastewater treatment
plants upstream. These treatment plants feed nutrient rich effluent (i.e., discharge
water) into the streams that then flow into these embayments. Adding additional
nutrients to an aquatic system has the potential to influence the type of
organisms that can live there.
I will use the organisms
I identify in the fish stomachs to construct a food web, which will allow me to
compare the diets of fish communities that reside in non-vegetated habitats,
such as shorelines and open water, to the fish communities that reside in
vegetated habitats, such as the submerged aquatic vegetation (SAV) beds.
question is interesting because in the 1980’s Gunston Cove was a hypereutrophic
(i.e., very nutrient rich) system, due to the nutrient rich effluent released
from the Noman M. Cole, Jr. Pollution Control Plant (NCPCP), which provided
ample nutrient resources for phytoplankton algae to grow. Eventually, the algae
became so abundant that it formed a thick green layer over much of Gunston
Cove, which blocked the sunlight from reaching the streambed, preventing the
growth of SAV. However, in an effort to reduce the occurrence of these harmful
algal blooms, NCPCP reduced the amount of nutrients released in their effluent
and after many years SAV beds began to reestablish (like they were prior to the
nutrients, such as phosphorus (the first nutrient that was reduced in the
wastewater effluent) and nitrogen, are better regulated, light is able to
penetrate the surface and in turn SAV is able to grow. The food webs I
construct will compare the potential impacts shifting from the
historically non-vegetated habitat to the emerging vegetated habitat may have
on the diets of fish in Gunston Cove and Hunting Creek.
Environmental Science student, I am very interested in the interactions that
take place between organisms within an ecosystem. One day I hope to incorporate
ecosystem modeling and spatial analysis into my own research, to investigate the
potential impact factors such as climate change or invasive species can have on
populations of aquatic species.
When I saw that
Dr. de Mutsert was looking for a student to help construct a food web, I
thought that this was a great place to start. Before I can create models to
predict how stressors such as climate change or invasive species will impact an
ecosystem, I must first understand how the species currently interact with
their environment and surrounding community.
Now, I begin
week seven of attempting to answer an unanswered question with high hopes and a
long to-do list. I have spent many hours this summer on a boat collecting fish
for my project, and macroinvertebrates
for my partner’s, trolling the internet and library for resources on how to
conduct a diet study and information on the history of the fish community in
the Potomac River. More recently I have begun processing my 196 fish samples to
try to understand what exactly is going on in the Potomac River (i.e., who is
eating whom). The past six weeks have been spent collecting my fish samples and
preparing the content in their stomachs to be examined.
With only two
weeks left until our results are due to our advisors, it is now time I use our
data to begin connecting the dots between the inhabitants of each embayment.
The only thing standing between the coveted answer and myself are approximately
190 fish stomachs, but have no fear – I’ve come prepared with my microscope,
tweezers, and coffee. Stay tuned to find out what happens next.