The seasonal biological surveys of 1971 / John C. Ayers, Samuel C. Mozley, John A. Stewart.

PHYTOPLANKTON

Techniques
Phytoplankton samples were collected by Nansen bottle at a depth of 1 m,
with the exception of the nearshore stations. Nearshore collections (serial
number zero stations) were made by submerging an open l-liter bottle 4 inches
below the water surface. All samples were l-liter whole samples. Each sample
was fixed with Utermohl's iodine fixative immediately after collection and
stored in an opaque container.
In the laboratory, each sample was concentrated to 100 ml by settling in
a 1000-ml graduate cylinder and siphoning off 900 ml of fluid. The concentra
ted sample was stored in a 100-ml opaque bottle.
Samples were prepared for counting by placing an aliquot of the concentrated sample in a tubular combination settling and counting chamber and
allowing the aliquot to settle overnight. The counting chamber containing th<
settled cells was then separated from the settling chamber, covered, and
placed on the microscope. The samples were counted on a binocular inverted
microscope at l000x magnification.
Solitary species, green and blue-green algae colonies, and the filaments
of filamentous forms were each counted as one cell. Each colonial diatom cel
was counted except when the size of the filaments or colonies prohibited
counting the individual cells; in this case, the number of individual cells
was estimated.
Results
Summary Table. The phytoplankton summary which follows (Table 3) is
based on the one used by the Michigan Water Resources Commission in reporting
their phytoplankton collections. Our summaries differ only in that we have
counted or estimated the cells in filamentous and colonial diatoms, while
the Commission counts a filament or colony as a single organism. The station
by-station phytoplankton records constitute Appendix B.
Dominant and Codominant Phytoplankters. In each phytoplankton sample,
one species or group typically was present in substantially greater numbers.
We have called these species or groups "dominant." In many stations one, two
or three additional species or groups challenged the numerical superiority of

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