Standard Operating Procedure for
Phytoplankton Analysis
1.0 Scope and Application
This method is utilized to identify, enumerate and measure phytoplankton taxa in samples collected
from the Great Lakes. Algal taxa are identified to the lowest taxonomic rank possible. A listing of
all organisms identified and their respective density and morphometric measurement for biovolume
calculation is reported.
2.0 Summary of Method
The method consists of two parts - analysis of phytoplankton (excluding most diatoms) and
analysis of diatom. For operational reasons, the first part of the analysis is also called "soft algae"
analysis. The "soft algae" are defined as those that are either naked or have a cellulosic cell wall
and cannot withstand acid digestion treatment. In contrast, diatoms have relatively "hard" silicious
valves and the valves can tolerate harsh acid treatment. Initially a preliminary scan is made of a
settled 10 mL sample in order to determine the volume to be used for each of the two analyses. For
the soft algae analysis, organisms are enumerated in a settling chamber using an inverted
microscope at 500x magnification. For diatom analyses, the samples are pretreated with strong
oxidants and the cleaned samples are mounted on glass slides and enumerated using a compound
microscope at 1250x magnification.