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A Trip to the Beach

Untangling the Mystery of Algal Blooms in the Great Lakes

Co Authors:

Susan E. Gass
Environmental Science Program
Dalhousie University

Laurie S. Eberhardt
Department of Biology
Valparaiso University


This interrupted case study, designed for an introductory biology or environmental science course, introduces students to the complexity of ecosystems by examining changes in trophic interactions and abiotic factors in a freshwater ecosystem as a result of human actions. The case narrative describes the recent and undesirable appearance of decomposing algae (Cladophora glomerata) on a public beach in the Laurentian Great Lakes. Students are asked to use the scientific method by creating hypotheses and examining observational data to describe biotic and abiotic components of the Great Lakes ecosystem. The case requires students to differentiate between benthic and pelagic environments (e.g., the influence of depth and phytoplankton density on light availability, and the availability of phosphorus) and the interactions between organisms in both environments. Students also examine shifts in these interactions as a result of the newly introduced zebra and quagga mussels, which have ultimately resulted in the algae's presence on the beach. There are also opportunities to discuss the impact of these ecosystem changes on people who own property and/or visit the beach.

  • Illustrate the aquatic food chain in the Great Lakes ecosystem.
  • List limiting factors to freshwater algae growth.
  • Describe the perturbations caused by the invasive mussel species in the Great Lakes ecosystem.
  • Model the scientific process of posing, testing, and rejecting hypotheses.
Keywords: invasive species; aquatic ecology; Great Lakes; trophic interactions; Cladophora; quagga mussels; zebra mussels; Lake Michigan; phosphorous
Topical Area: Scientific method, Scientific argumentation
Educational Level: Undergraduate lower division
Formats: PDF
Type/Method: Directed, Interrupted
Language: English
Subject Headings: Biology (General)   Ecology   Environmental Science   Limnology   Zoology  
Date Posted: 7/28/2016
Date Modified: N/A
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

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