Case Study:
Name: ___________________________
The Spring Phytoplankton Bloom in Puget Sound
1) Examine the temperature, salinity, and potential density graphs for a full year (on
slide) and from April to June (on handout). How does water column mixing and
stratification change as you move through the spring months?
2) Now examine the dissolved inorganic nitrogen graph (on slide). During what season
are nutrient concentrations high and when are they low? Given what you know
about the sources of nutrients and stratification, how do you account for this?
3) Given that phytoplankton grow most rapidly when there is ample light and
nutrients concentrated in a surface layer, draw a line showing diatom abundance on
the diatom graph (see reverse) starting in the winter and going through to the
summer.
4) Think about how you expect zooplankton abundance to respond to phytoplankton
abundance, and vice versa. On the zooplankton graph (reverse), draw a line on the
graph showing zooplankton abundance from the winter and through the spring and
into the summer.
5) Draw two lines on the bacterial graph (reverse), one representing cyanobacteria,
one representing heterotrophic bacteria. Think about how cyanobacteria will
respond to the light and nutrient levels, and how will heterotrophic bacteria will
respond to the decaying biomass.
6) Look at the graphs on the handout. What explains the changes in nitrate abundance
as you move through the spring months? Silicate abundance? What do you think will
happen to nutrient abundance after all these organisms die?
Abundance of diatoms 
spring
summer
winter
spring
summer
winter
spring
fall
winter
Abundance of zooplankton 
winter
winter
fall
winter
Abundance of bacteria 
fall
summer