Food Chain Effects of Zebra Mussel (revised 7/22)
Notes to faculty
Outcomes: Students appreciate the effects of an introduced species on organisms in an
ecosystem. They gain experience working with data in a figure. They demonstrate
principled understanding of carbon movement/transformation through a simple aquatic
food chain.
What students do: They are briefly told the “zebra mussel story” and given data on
chlorophyll-a concentrations and Secchi disk depths in Seneca Lake after zebra mussel
introduction. They draw a box-and-arrow diagram of the flow of carbon in this system.
What to pay particular attention to: Some students have difficulty translating their
understanding of food chain processes from one context to another, in this case to an
aquatic ecosystem. Working in groups should be helpful here. Challenging steps may
be: photosynthesis in water – that the outcome is the same as in terrestrial systems,
decomposition of mussel fecal pellets through microbial decomposition-cellular
respiration (although, again, this is the same process that occurs in soils), and loss of
CO2 from animals through cellular respiration (perhaps some students will not recognize
mussels as ‘animals’ and some students may not recognize carbon as matter when it is
in a gaseous form). The idea here is that students will better understand these
processes (photosynthesis, respiration, transformation) by thinking about them in a
different type of ecosystem and by learning to explicitly apply the principle of
conservation of matter – taking what they know from terrestrial systems to an aquatic
one.
Logistics:
o Students can work in groups on this exercise in many different ways.
o You will need to practice the “Step One-Step Two” approach to reading and
interpreting figures ahead of time in class.
o Students will need experience with box-and-arrow diagrams before they do this
exercise. You can give them a specific example of what you are looking for from
another type of ecosystem.
o Aspects of the C cycle that may be confusing are: dissolution of CO2 in water
(you may need to briefly explain this), a double y axis (although the directions do
explain this), and what happens to fecal pellets (they sink, are decomposed).
o You could introduce the exercise with photos and other images from the web.
Some are listed below,
o The image is light; you can reproduce it from the URL.
Units & Quantitative Skills: phytoplankton measurements and data; data in a figure
translated to words.
Information specific to the activity: C transformations (e.g. photosynthesis, carbonic acid)
in water, introduced species
Resources
There is a great deal of information about zebra mussels on the web. In addition
to the images below, see:
o
o
o
o
USDA (http://www.invasivespeciesinfo.gov/aquatics/zebramussel.shtml)
National Atlas (http://www.nationalatlas.gov/articles/biology/a_zm.html)
Gulf States Fish. Com.
(http://nis.gsmfc.org/nis_factsheet.php?toc_id=131)
TIEE (http://tiee.ecoed.net/vol/v1/figure_sets/species/species_figs.html)
HIDDEN CURRICULUM ADDRESSED
• Principles: Conservation of Matter (assimilation of carbon by producers, transfer of
carbon from producers to consumers, transfer of carbon from producers/consumers to
decomposers, transfer of carbon to atmosphere during respiration by all organisms in the food
chain)
Processes: Generation (photosynthesis); Transformation (building of biomolecules
within an organism, consumption of one organism by another); Oxidation (autotrophic
respiration, heterotrophic respiration, decomposition)
• Scale & Time: Processes across atomic/molecular-organismal-ecosystem scales.
• Forms & Representations: Ecosystem matter flow (box-arrow diagrams; grouping of
individuals into trophic levels)
Student Directions
Someone in your group should read the information and questions below. Be sure you
all understand what is being said and shown before you move on.
Zebra Mussels (Dreissena polymorpha), a Eurasian species, were first discovered in
Lake St. Clair (Detroit) in 1988. They were unintentionally brought into the U.S. in ballast
water of ocean traveling ships (ballast water in the bottom of ships controls buoyancy).
They spread very rapidly over North America due in part to prolific reproduction (females
can lay over one million eggs) and lack of predators here. Now Zebra Mussels are a real
nuisance in many places, including the Great Lakes (see images below).
Spread of zebra mussels (pink) from 1988-1997 in the U.S.
www.crwr.utexas.edu/.../image014.jpg
Zebra mussels coating a shopping cart left in the water for a few weeks in the Great Lakes
(www.epa.gov/glnpo/atlas/glat-ch4.html).
Zebra mussels were first detected in Seneca Lake, one of the NY Finger Lakes, in
1992. These animals filter-feed very large volumes of phytoplankton (microscopic
floating algae). Plants (including algae) use the green pigment Chlorophyll-a to convert
sunlight energy into sugars in the process of photosynthesis. Therefore, scientists use
Chlorophyll-a to measure biomass of phytoplankton in water. Phytoplankton are an
important part of the aquatic food web because they are the primary producers of food
for zooplankton and fish.
The title of the graph below is “Average Secchi and Chlorophyll a Seneca”. The graph
shows changes from 1992-2004 in Chlorophll-a (line with diamonds); the values are
averages in micrograms per liter and are on the left hand size vertical axis.
Photosynthetic organisms (in this case algae in the water) use chlorophyll to
photosynthesize and therefore the amount of this pigment can be used to measure plant
biomass. The other line is the Secchi Depth; this is a simple-to-measure indication of the
turbidity of the water. To get this value, the scientist drops a white and black disk (about
the size of a dinner plate) attached to a rope over the side of a boat. The Secchi Disk
Depth is the depth at which s/he can no longer see the disk. The units are meters below
the surface of the water (0 is the water surface)and is on the right hand side vertical axis.
From: fli.hws.edu/sos/zebra_teacher.asp
Address the following questions:
1. To understand and interpret this graph, use this two-step approach. First
describe the graph – the axes, the legends, the lines. For the second step,
interpret the graph. Write your answers below, along with any questions you may
have.
o Step One:
o
Step Two:
2. Zebra mussels feed by filtering water through their gills (here they are filtering
out the microscopic floating algae). They are not very efficient in their feeding
and consequently excrete organic-rich fecal pellets which fall to the bottom of the
lake. In the space below, draw a box-and-arrow diagram showing the movement
of carbon through the Seneca Lake food chain after introduction of the mussels.
Include the different forms that the carbon is in plus the major processes. (Note:
carbon dioxide dissolves in water).