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The Dead Zone

Ecology and Oceanography in the Gulf of Mexico


Kathleen Archer
Biology Department
Trinity College
Lauren Sahl
Corning School of Ocean Studies
Maine Maritime Academy


This interrupted case study focuses on the seasonal hypoxic area in the Gulf of Mexico known as the Dead Zone. It follows Sue, a college student, whose father is a commercial fisherman affected by the lack of fish in his usual fishing grounds in the summer.  In her quest to determine why the fish disappear, Sue learns about both the biological and physical forces that produce, maintain, and eventually dissipate the hypoxic zone. The case introduces students to the marine food web, the aquatic microbial loop, the impact of exogenous nutrients, and the physical forces that affect oxygen content and water stratification. It could be used in introductory biology or ecology courses or in an oceanography course.


  • Understand the close integration of biological and physical influences on an aquatic environment and the outcome when nutrient inputs are elevated.
  • Understand the structure of an aquatic food web.
  • Understand the role of the microbial loop.
  • Understand the role of salinity and temperature in creating water column density structure.
  • Understand how the interaction between biological processes and water column structure can cause hypoxia.
  • Read and interpret graphical data.


Gulf of Mexico; microbial loop; dissolved oxygen; aquatic hypoxia; nutrients; fertilizer; algae; marine food web; phytoplankton; nitrogen; water column; seawater; salinity

Topical Areas

Policy issues

Educational Level

Undergraduate lower division, Undergraduate upper division



Type / Methods

Interrupted, Demonstration



Subject Headings

Ecology  |   Environmental Science  |   Earth Science  |   Marine Science / Oceanography  |   Botany / Plant Science  |  

Date Posted


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Eric Ribbens
Western Illinois University
Macomb, IL
I really like this case, in part because it nicely replicates how science works, gradually narrowing the possible explanations and using data to eliminate ideas and reinforce others. For a recent update on this issue, read the following article: "Runoff from Iowa farms growing concern in Gulf Written" by Perry Beeman Oct. 28, 2012,