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:
- 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).