Transcript Henry Schmitx

The Effect of Bythotrephes longimanus on Copepod Populations in Lake Mendota
Henry Schmit with Jake Walsh and Dr. Jake Vander Zanden
UW Hasler Center for Limnology
Background
Data/Methods
Copepods are a type of native microscopic crustacean that
play an intrinsic role in the ecosystem of many lakes. The
invasive predatory zooplankter, Bythotrephes longimanus,
was first detected in Lake Mendota in 2009 (Vander Zanden,
personal communication), but its effects on native copepod
communities are poorly understood (Lathrop et al., 2002). In
Lake Mendota, cyclopoids consist of two main species
Diacyclops thomasi and Mesocyclops edax.
In order to count zooplankton a mesh net is dropped down and then drawn
up; the contents of the net are then washed with ethanol into a jar. At the lab,
the zooplankton were suspended in water and from that a subsample was
analyzed.
Research question
Have copepod populations in Lake Mendota changed since
the spiny water flea invasion, and if so why?
Near the center of Lake Mendota, data were gathered by letting a plankton
net drift down 15 meters and then pulling it up at a constant rate of three
seconds per meter. The mesh size of the net is 83um. The net was always
dropped at a point marked by a buoy that measures temperature and other
parameters. The plankton at the bottom of the net then were sprayed with
ethanol, washing them into a jar.
Analysis
Diacyclops thomasi, Cyclopoid copepod density over several years (1995-2013). The y-axis
is a logarithmic plot. The vertical dashed line indicates the approximate date of the
invasion of the spiny water flea.
Mesocyclops edax, Cyclopoid copepod density over several years (1995-2013). The yaxis is a logarithmic plot. The vertical dashed line indicates the approximate date of the
invasion of the spiny water flea.
A subsample of the data were analysed in the lab under a microscope by
counting the number and kind of plankton. This procedure consisted of:
● putting the sample with the ethanol through a 35 or 80 um mesh
● rinsing it into a beaker with water until it was filed to the 140 ml mark
● a 1 ml subsample was drawn using Hensen-Stempel pipette
● the sub-sample was put onto a counting wheel for examining under the
microscope.
Some types of plankton were identified down to the species, while others
were not.
Diacyclops thomasi,(left panel), Mesocyclops edax, (right panel), USGS
Mesh cup
Nauplii density over several years (1995-2013). The y-axis is a logarithmic plot. The vertical
dashed line indicates the approximate date of the invasion of the spiny water flea.
Copepodite copepod density over several years (1995-2013). The y-axis is a logarithmic plot.
The vertical dashed line indicates the approximate date of the invasion of the spiny water flea.
Hensen-Stempel Pipette
Limited research has been done on these animals and how they
affect aquatic food webs. They eat plankton earlier in their
development, then turn carnivorous, eating more zooplankton,
daphnia, and younger copepods as they grow older (Confer, 1971).
Copepods are eaten by planktivorous fish.
M. edax
D. thomasi
Calanoids
Before invasion 1995-2008 (n=210)
2.19
3.60
4.86
3.51
0
After invasion
0.64
3.43
5.12
3.46
0.89
Years
If their numbers are decreasing it may be from direct spiny water
flea predation or spiny water fleas eating their prey such as
Daphnia. If their numbers are increasing it may be from spiny water
fleas eating their competition (Rollwagen-Bollens et al., 2013).
Ward counting wheel
2009-2013 (n=74)
and Oceanography 16.4 (1971): 663-66. JSTOR. Web. 19 Aug. 2014.
<http://www.jstor.org.ezproxy.library.wisc.edu/stable/2834186>.
Lathrop, R. C., Johnson, B. M., Johnson, T. B., Vogelsang, M. T., Carpenter, S. R., Hrabik, T. R., Kitchell,
J. F., Magnuson, J. J., Rudstam, L. G. and Stewart, R. S. (2002), Stocking piscivores to improve fishing and
Copepodites
B. longimanus
Logarithmic average of Mesocyclops edax, Diacyclops thomasi, Calanoids, Copepodites, and Bythotrephes longimanus before and after the spiny water flea invasion.
Summary
References
Confer, John L. "Intrazooplankton Predation by Mesocyclops Edax at Natural Prey Densities." Limnology
Calanoid copepod density over several years (1995-2013). The y-axis is a logarithmic plot. The
vertical dashed line indicates the approximate date of the invasion of the spiny water flea.
It was discovered that M. edax population density was reduced by an order of magnitude after the B.
longimanus invasion. However, D. thomasi and Calanoids increased after the invasion, which may have
occurred because of reduced competition from M. edax and Daphnia pulicaria, a dominant grazing
zooplankton in Lake Mendota that has been negatively impacted by B. longimanus predation. However in 2013
the number of D. thomasi sharply dropped off, and we are not sure why. The number of Copepodites increased
in 2011 most likely because they did not reach full size and so could not be identified down to the species.
water clarity: a synthesis of the Lake Mendota biomanipulation project. Freshwater Biology, 47: 2410–2424.
Links
doi: 10.1046/j.1365-2427.2002.01011.x
Rollwagen-Bollens, Gretchen, Stephen M. Bollens, Alejandro Gonzalez, Julie Zimmerman, Tammy Lee, and
Josh Emerson. "Feeding Dynamics of the Copepod Diacyclops Thomasi Before, during and following
Filamentous Cyanobacteria Blooms in a Large, Shallow Temperate Lake - Springer." Feeding Dynamics of
Spiny Water Flea (Bythotrephes Longimanus) Photo by Jake Walsh
http://www.glsc.usgs.gov/greatlakescopepods/Detail.php?GROUP=Cyclopoid&SPECIES=Diacyclops%20thomasi
http://www.glsc.usgs.gov/greatlakescopepods/Detail.php?GROUP=Cyclopoid&SPECIES=Mesocyclops%20edax
the Copepod Diacyclops Thomasi Before, during and following Filamentous Cyanobacteria Blooms in a
http://limnology.wisc.edu/blog/invasive-spiny-water-flea-found-in-trout-lake
Large, Shallow Temperate Lake - Springer. Hydrobiologia, 01 Mar. 2013. Web. 17 Aug. 2014.
http://limnology.wisc.edu
<http://link.springer.com/article/10.1007/s10750-012-1385-5>.
Acknowledgements
Thanks to the Long Term Ecological Research (LTER)
network, and the Science Research Internship program.
Another thanks to the UW students who worked in the lab:
Bridget, Jared, and Sam.