Rob provided a tangible exercise for exploring nutrient-phytoplankton-zooplankton interaction — using toothpicks, styrofoam balls, and styrofoam cups as surrogates for their equivalents in the bay.



Students performed four physical transactions to represent events in the bay:

1. Adding a toothpick from one bin to an available styrofoam ball to represent the uptake of nutrients by phytoplankton (thus giving life).
2. Disassembling five styrofoam balls with embedded toothpicks and placing the toothpicks in a styrofoam cup while returning the styrofoam balls to a second bin (to represent zooplankton feeding upon phytoplankton and giving the zooplankton life).
3. Removing a toothpick from a styrofoam ball and returning the parts to bins 1 and 2 (to represent death of phytoplankton)
4. Removing toothpicks from a styrofoam cup and returning the toothpicks to the first bin (to represent death of zooplankton)

Rob suggested an initial game plan for performing the tasks:

1. Create phytoplankton until all the toothpicks are used.
2. Create one zooplankton by feeding it five phytoplankton.
3. Perform simulated timesteps of phytoplankton and zooplankton with the requirements that:
   • if the number of phytoplankton in "Narragansett Bay" is greater than the number required for the zooplankton to survive, they "eat" 5 phytoplankton for each zooplankton (take toothpicks from the eaten phytoplankton and add to the zooplankton and return dead phytoplankton ball to future phytoplankton reservoir)
   • if the number of phytoplankton in "Narragansett Bay" is less than or equal to the number required to survive, then the zooplankton dies (take toothpicks from the dead zooplankton and add to the nutrient reservoir and return dead zooplankton ball to zooplankton reservoir)

The actions were recorded in "steps" within a recording spreadsheet that then fed time series charts embedded in the spreadsheet. After 92 steps, the charts appeared as:



Students discussed the tangible transactions that were available and debated how best to represent a feasible progression within the bay. After performing the tasks in sequences representative of the outline given them, they came to the conclusion that existing animals would have to eat every step. As a result there was a higher rate of death and a limitation of nutrients even after an additional ten toothpicks were made available.

Rob facilitated a discussion of the insights that emerged from doing physical tasks with tangible objects. Like the sharks-stripers exercise from the first day of class, the exercise would be relevant for the class activities to follow in the NPDZ model development phase of the course.