NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE

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1 CASE TEACHING NOTES for Fish as Fertilizer: The Impacts of Salmon on Coastal Ecosystems by Mark L. Kuhlmann, Biology Department, Hartwick College, Oneonta, NY INTRODUCTION / BACKGROUND In this case study, students examine data from a number of published studies of the effects of Pacific salmon on freshwater and riparian ecosystems. The case focuses on the interesting phenomenon of spawning salmon acting as nutrient conveyor belts, transporting nutrients from the ocean upstream into freshwater spawning areas and, in some cases, even onto land, reversing the more typical downstream movement of nutrients. As students work at analyzing and interpreting graphical data, they will also increase their understanding of the principles of biogeochemical cycling and gain an appreciation for the interconnectedness of different types of ecosystems. This case study is appropriate for students with at least an introductory background in ecology such as would be gained in most introductory biology courses. The topic is appropriate for any course covering ecosystem ecology (e.g., general ecology, freshwater or marine ecology, environmental science). Students should have a general knowledge of food webs and biogeochemical cycling, and should also be introduced to the basics of the Pacific salmon life cycle and the technique of stable isotope analysis. Summaries of the latter two topics are presented in the General Backgound section of the case study and can either be presented by the instructor in class or given to the students as a reading assignment prior to starting the case. Because Pacific salmon support an important commercial fishery and are of significant conservation concern, this case study can easily be extended to include applied issues such as conservation biology or fisheries management. For example, it is relatively easy to estimate the effect of decreased salmon stocks on the delivery of nutrients to spawning streams, or diagram changes in the pattern of nutrient delivery caused by changes in land use (dams, deforestation, etc.). Data on changes in salmon stocks and per-capita nutrient content as well as samples of these kinds of calculations are available in several of the references listed under Additional Sources below. Objectives The objectives of this case are for students to: Be able to analyze, interpret, and draw conclusions from graphical and tabular data. Be familiar with the principles and significance of biogeochemical cycling. Understand connections between marine, aquatic, and riparian ecosystems. Understand the differences between experimental and observational studies. Case Summary Table Part Suggested Method Cognitive skill Class size / Time Part 1 Do salmon add marine-derived nitrogen to the stream ecosystem? Part 2 Do marine-derived nutrients affect stream organisms? Part 3 How does marine-derived nitrogen get to stream-side terrestrial ecosystems? Part 4 Does salmon-derived nitrogen affect the terrestrial ecosystem? Think-Pair-Share Comprehension, analysis Any/Moderate Jigsaw Informal group work Think-Pair-Share Comprehension, analysis, synthesis Comprehension, analysis, synthesis, evaluation Comprehension, analysis, synthesis Small/Long Any/Moderate Any/Moderate Page 1

2 CLASSROOM MANAGEMENT This case study is designed to be used as a major course unit on the ecology of ecosystems and will take around six to eight (50- to 60-minute) class periods to complete, depending on how much background information needs to be covered and how much of the group work is done in class. The amount of class time can be decreased by assigning some of the small-group work as homework. Most of the parts of the case will also work as independent units that could be completed in one or a few class periods. General Background Students need some background on biogeochemical cycling, salmon life history, and the use of stable isotopes for tracing marine-derived nutrients. This can either be presented as an introductory lecture or lectures or by assigning the General Background section of the case as reading, perhaps supplemented by appropriate sections of the course textbook. This material will take at least one hour of class time to present, more if the students have little previous background in biogeochemical cycling. Part 1 Students should read the background information for this section, then work with a small group to understand the figures and answer the questions. This can be followed by a class discussion of the figures and questions. I often call on students to describe and explain each figure or share their answers to the questions. This part will take 1 to 1.5 (50- to 60-min.) class period(s). For students not familiar with aquatic macroinvertebrates, the Resources section below lists several websites with descriptions, drawings, or photographs of representative examples. Part 2 (2A, 2B, and 2C) This section uses a three-way jigsaw to examine the effects of marine-derived nutrients (MDNs) on different groups of stream organisms. The first set of groups each get one section of figures with questions to work on; the members of one group become experts on their figure(s). When the first groups are done, reorganize the class into new groupings, each containing one member from each of the original groups. In the second grouping, students explain the figures to each other; the expert for each section should take the lead on the figure(s) from his/her first group. When the second grouping is done, all students should understand what each of the figures shows and understand the answers to the questions with each figure. To finish, each group should work together to answer the last two questions. See the Resources section below for more information on using the jigsaw method. This section is the longest and will likely take at least two class periods since each student in the second grouping will need time to explain the figures and answers to the others in their group. Group work can be followed by a class discussion of the figures, but I find that, through the process of the jigsaw, most students understand all the figures at the end. However, a short class discussion of the Second Jigsaw Group questions (in Part 2) may still be useful. Part 3 Students should read the background information for this section, then work with a small group to understand the figures and answer the questions. This can be followed by a class discussion of the figures and questions. I often call on students to describe and explain each figure or share their answers to the questions. This part will take 1 to 1.5 class period(s). Part 4 Students should read the background information for this section, then work with a small group to understand the figures and answer the questions. This can be followed by a class discussion of the figures and questions. I often call on students to describe and explain each figure or share their answers to the questions. This part will take approximately 1 class period. Closure If all or most of the sections of this case have been used, it may be useful to have the class review all the different interactions to get a complete picture of the connections within and between the different ecosystems. A partial diagram of interactions between salmon and stream and riparian ecosystems, including pathways of nutrient flows, is given below in Figure 1. [For a somewhat simpler diagram focusing on nutrient pathways, see Figure 3 in Gende et al. (2002).] One of the interesting implications of the research in this system is the possibility of positive feedback loops to the salmon. That is, the nutrients of the dead salmon might benefit their own offspring. One loop is through the stream food web: salmon carcasses increase growth in juvenile salmon, probably by increasing the Page 2

3 Figure 1: A partial diagram of known and hypothesized effects of salmon on stream and riparian ecosystems. LWD = large woody debris. abundance of juvenile salmon prey. More complicated and more speculative is feedback from the riparian community. Salmon nutrients stimulate growth in riparian plants, which could result in lower sediment loads (by decreasing erosion), cooler stream temperatures (through shading), and more hiding places for juvenile salmon (through inputs of course woody debris ), all beneficial for juvenile salmon. More abundant or nutrient-rich vegetation could also result in higher allochthonous inputs (organic matter in the form of leaves, sticks, cones, bark, branches, etc.) to the stream, feeding back to salmon through the stream food web. Since the students will be doing considerable work in small groups, you might want to assess individual contributions to the group assignment, particularly if much of the work is done outside of class. See the last entry in the Resources section for an example of a peer evaluation method and form that is available online. Student Assessment Below are several suggestions for assessing students overall understanding of the case study. The diagram quiz essentially asks students to construct a concept map of the whole case. For more information about concept mapping, see the Resources section. Short essay quiz: Many salmon stocks in the Pacific Northwest have declined greatly since the mid- 1800s. What effects might this decline have on both stream and riparian ecosystems? Try to incorporate as many of the ecosystem components and effects that you learned about from the figures in the case as you can. Short essay quiz: Some researchers call Pacific salmon keystone species in coastal ecosystems. A keystone species is one that has a disproportionate and widespread impact within its ecosystem or community. Based on what you learned in this case study, do you think salmon are keystone species? Page 3

4 Support your answer with evidence from the research studies you examined. Diagram quiz: Make as complete a diagram as you can of the movement of nutrients from the ocean into components of the stream and riparian ecosystem. Label each component in your diagram. Between components, write a phrase or sentence that clearly describes the relationship or connection between the components. ANSWER KEY Answers to the questions posed in the case study are provided in a separate answer key to the case. Those answers are password-protected. To access the answers for this case, go to the key. You will be prompted for a username and password. If you have not yet registered with us, you can see whether you are eligible for an account by reviewing our password policy and then apply online or write to answerkey@sciencecases.org. REFERENCES Overviews / Background Information Cederholm, C.J., M.D. Kunze, T. Muroat, and A. Sibatani Pacific salmon carcasses: Essential contributions of nutrients and energy for aquatic and terrestrial ecosystems. Fisheries 24:6 15. Gende, S.M., R.T. Edwards, M.F. Willson, and M.S. Wipfli Pacific salmon in aquatic and terrestrial ecosystems. BioScience 52: Moore, J.W Animal ecosystem engineers in streams. BioScience 56: Naiman, R.J., R.E. Bilby, D.E. Schindler, and J.H. Helfield Pacific salmon, nutrients, and the dynamics of freshwater and riparian ecosystems. Ecosystem 5: National Research Council (U.S.). Committee on Protection and Management of Pacific Northwest Anadromous Salmonids Upstream: Salmon and Society in the Pacific Northwest. Washington, D.C.: National Academy Press. Peterson, B.J., and B. Fry Stable isotopes in ecosystem studies. Annual Review of Ecology and Systematics 18: Reimchen, T.E Salmon nutrients, nitrogen isotopes and coastal forests. Ecoforestry Fall 2001: Ruckelshaus, M., P. Levin, J.B. Johnson, and P.M. Kareiva The Pacific salmon wars: What science brings to the challenge of recovering species. Annual Review of Ecology and Systematics 33: Schindler, D.E., M.D. Scheuerell, J.W. Moore, S.M. Gende, R.B. Francis, and W.J. Palen Pacific salmon and the ecology of coastal ecosystems. Frontiers in Ecology and the Environment 1: Vanni, M.J Nutrient cycling by animals in freshwater ecosystems. Annual Review of Ecology and Systematics 33:341. Main Sources Bilby, R.E., B.R. Fransen, and P.A. Bisson Incorporation of nitrogen and carbon from spawning coho salmon into the trophic system of small streams: Evidence form stable isotopes. Canadian Journal of Fisheries and Aquatic Science 53: Chaloner, D.T., K.M. Martin, M.S. Wipfli, P.H. Ostrom, and G.A. Lamberti Marine carbon and nitrogen in southeastern Alaska stream food webs: Evidence from artificial and natural streams. Canadian Journal of Fisheries and Aquatic Sciences 59: Helfield, J.M., and R.J. Naiman Effects of salmon-derived nitrogen on riparian forest growth and implications for stream productivity. Ecology 82: Hilderbrand, G.V., T.A. Hanley, C.T. Robbins, and C.C. Schwartz Role of brown bears (Ursus arctos) in the flow of marine nitrogen into a terrestrial ecosystem. Oecologia 121: Hocking, M., and T. Reimchen Salmon-derived nitrogen in terrestrial invertebrates from coniferous forests of the Pacific Northwest. BMC Ecology 2:4. Mathewson, D., M. Hocking, and T. Reimchen Nitrogen uptake in riparian plant communities across a sharp ecological boundary of salmon density. BMC Ecology 3:4. Peterson, D.P., and C.J. Foote Disturbance of small-stream habitat by spawning sockeye salmon in Alaska. Transactions of the American Fisheries Society 129: Wipfli, M.S., J. Hudson, and J. Caoutte Influence of salmon carcasses on stream productivity: Response of biofilm and benthic macroinvertebrates in southeastern Alaska. Canadian Journal of Fisheries and Aquatic Science 55: Wipfli, M.S., J.P. Hudson, and J.P. Caouette Marine subsidies in freshwater ecosystems: Salmon carcasses increase the growth rates of stream-resident salmonids. Transactions of the American Fisheries Society 132: Page 4

5 Additional Sources Ben-David, M Timing of reproduction in wild mink: The influence of spawning salmon. Canadian Journal of Zoology 75: Ben-David, M., T.A. Hanley, and D.M. Schell Fertilization of terrestrial vegetation by spawning Pacific salmon: The role of flooding and predator activity. Oikos 83: Bilby, R.E., B.R. Fransen, P.A. Bisson, and J.K. Walter Response of juvenile coho salmon (Oncorhynchus kisutch) and steelhead (Oncorhynchus mykiss) to the addition of salmon carcasses to two streams in southwestern Washington, U.S.A. Canadian Journal of Fisheries and Aquatic Science 55: Chaloner, D.T., G.A. Lamberti, R.W. Merritt, N.L. Mitchell, P.H. Ostrom, and M.S. Wipfli Variation in responses to spawning Pacific salmon among three south-eastern Alaska streams. Freshwater Biology 49: Drake, D.C., R.J. Naiman, and J.M. Helfield Reconstructing salmon abundance in rivers: An initial dendrochronological evaluation. Ecology 83: Finney, B.P., I. Gregory-Eaves, J. Sweetman, M.S.V. Douglas, and J.P. Smol Impacts of fishing and climatic change on Pacific salmon abundance over the past 300 years. Science 290: Francis, T.B., D.E. Schindler, and J.W. Moore Aquatic insects play a minor role in dispersing salmon-derived nutrients into riparian forests in southwestern Alaska. Canadian Journal of Fisheries and Aquatic Sciences 63: Gresh, R., J. Lichatowich, and P. Schoonmaker An estimation of historic and current levels of salmon production in the Northeast Pacific ecosystem. Fisheries 25: Helfield, J., and R. Naiman Salmon and alder as nitrogen sources to riparian forests in a boreal Alaskan watershed. Oecologia 133: Helfield, J., and R. Naiman Keystone interactions: Salmon and bear in riparian forests of Alaska. Ecosystems 9: Kline, T.C., J.J. Goering, O.A. Mathisen, P.H. Poe, and P.L. Parker Recycling of elements transported by runs of Pacific salmon: I. 15N and 13C evidence in Sashin Creek, southeastern Alaska. Canadian Journal of Fisheries and Aquatic Sciences 47: Kline, T.C., J.J. Goering, O.A. Mathisen, P.H. Poe, P.L. Parker, and R.S. Scalan Recycling of elements transported by runs of Pacific salmon: II. 15N and 13C evidence in the Kvichak River waterhshed, Bristol Bay, southeastern Alaska. Canadian Journal of Fisheries and Aquatic Sciences 50: Larkin, G.A., and P.A. Slaney Implications of trends in marine-derived nutrient influx to south coastal British Columbia salmonid production. Fisheries 22: Meehan, E.P., E.E. Seminet-Reneau, and T.P. Quinn Bear predation on Pacific salmon facilitates colonization of carcasses by fly maggots. American Midland Naturalist 153: Merz, J.E., and P.B. Moyle Salmon, wildlife, and wine: Marine-derived nutrients in humandominated ecosystems of Central California. Ecological Applications 16: Minakawa, N., and R.I. Gara Ecological effects of a chum salmon (Oncorhynchus keta) spawning run in a small stream of the Pacific Northwest. Journal of Freshwater Ecology 14: Minakawa, N., R.I. Gara, and J.M. Honea Increased individual growth rate and community biomass of stream insects associated with salmon carcasses. Journal of the North American Benthological Society 21: Mitchell, N.L., and G.A. Lamberti Responses in dissolved nutrients and epilithon abundance to spawning salmon in southeast Alaska streams. Limnology and Oceanography 50: Moore, J., D.E. Schindler, and M.D. Scheuerell Disturbance of freshwater habitats by anadromous salmon in Alaska. Oecologia 139: Moore, J.W., and D.E. Schindler Nutrient export from freshwater ecosystems by anadromous sockeye salmon (Oncorhynchus nerka). Canadian Journal of Fisheries and Aquatic Sciences 61: Moore, J.W., D.E. Schindler, J.L. Carter, J. Fox, J. Griffiths, and G.W. Holtgrieve Biotic control of stream fluxes: Spawning salmon drive nutrient and matter export. Ecology 88: Reimchen, T.E Some ecological and evolutionary aspects of bear-salmon interactions in coastal British Columbia. Canadian Journal of Zoology 78: Scheuerell, M.D., P.S. Levin, R.W. Zabel, J.G. Williams, and B.L. Sanderson A new perspective on the importance of marine-derived nutrients to threatened stocks of Pacific salmon (Oncorhynchus spp.). Canadian Journal of Fisheries and Aquatic Sciences 62: Page 5

6 Schindler, D.E., P.R. Leavitt, C.S. Brock, S.P. Johnson, and P.D. Quay Marine-derived nutrients, commercial fisheries, and production of salmon and lake algae in Alaska. Ecology 86:3225. Walter, J.K., R.E. Bilby, and B.R. Fransen Effects of Pacific salmon spawning and carcass availability on the caddisfly Ecclisomyia conspersa (Trichoptera: Limnephilidae). Freshwater Biology 51: Wilkinson, C.E., M.D. Hocking, and T.E. Reimchen Uptake of salmon-derived nitrogen by mosses and liverworts in coastal British Columbia. Oikos 108: Willson, M.F., and K.C. Halupka Anadromous fish as keystone species in vertebrate communities. Conservation Biology 9: Winder, M., D.E. Schindler, J.W. Moore, S.P. Johnson, and W.J. Palen Do bears facilitate transfer of salmon resources to aquatic macroinvertebrates? Canadian Journal of Fisheries and Aquatic Sciences 62: Wipfli, M.S., J. Hudson, D.T. Chaloner, and J. Caoutte Influence of salmon spawner densities on stream productivity in Southeast Alaska. Canadian Journal of Fisheries and Aquatic Science 56: RESOURCES Underwood, C The Salmon Forest. Bullfrog Films, Oley, PA. Documentary video. This video examines the complex rain forest ecosystem along the northern Pacific coast of British Columbia. It shows how the salmon provides nutrients for the forest, biodiversity of insect life in the rain forest canopy and how native peoples depend on this ecosystem to sustain themselves. See bullfrogfilms.com/catalog/sal.html for ordering information. [Last accessed: 2/16/09] Pacific salmon information. These sites have information and links to salmon biology, conservation, and recovery plans: Oregon Sea Grant Marine Education. oregonstate.edu/links/index.html#salmon (scroll to Salmon ) [Last accessed: 2/16/09] Salmon Populations, NOAA s National Marine Fisheries Resources, Northwest Regional Office. Populations/Index.cfm [Last accessed: 2/16/09] Salmon Recovery, Washington Department of Fish and Wildlife. recovery.htm [Last accessed: 2/16/09] Wild Salmon Our Precious Natural Resource, Washington Department of Fish and Wildlife. [Last accessed: 2/16/09] Short introduction to the impact of salmon on riparian forests, from the David Suzuki Foundation, research sponsor and producer of the Salmon Forest video listed above: Science.asp [Last accessed: 2/16/09] Overview of research by Dr. T. Reimchen s lab: [Last accessed: 2/16/09] Overview of stable isotope analysis: [Last accessed: 2/16/09] Overview of biogeochemical cycles: html [Last accessed: 2/16/09] Pictures or photographs of macroinvertebrates: invertebrates.html [Last accessed: 2/16/09] Information on concept mapping from Wikipedia; entry includes links to additional information: [Last accessed: 2/16/09] Information about using the jigsaw method in case studies: [Last accessed: 2/16/09] teaching/jigsaw.html Short article describing methods for assessing students when using case studies, including a good example of peer-evaluation of group work: teaching/justice.html [Last accessed: 2/16/09] Acknowledgements: Thanks to the students in several rounds of my aquatic ecology class for field-testing versions of this case. Mary Allen and three anonymous reviewers provided helpful suggestions on earlier drafts. Thanks also to Hartwick College s Pine Lake Environmental Campus for a quiet and beautiful place to write. Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Originally published March 27, Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work. Page 6