The phytoplankton of the Cook Plant monthly minimal surveys during the preoperational years 1972, 1973, and 1974 / by John C. Ayers.

PHYTOPLANKTON ABUNDANCES 1972 THROUGH 1974

The nine sampling stations of the monthly minimal surveys provide a means
of assessing whether there has been increase of the phytoplankton population.
The cells per ml data initially were condensed spatially by averaging the data
from all nine stations for each month. Inspection of the results, however,
suggested that in many of the surveys the counts were higher at stations near
the shore, accordingly the nine short-survey stations have been separated
into an inshore and an offshore group. The inshore group includes the stations
situated at a half mile or less from the shore; these are stations DC-O, DC-1,
NDC-.5-1, and SDC-.5-1. The offshore group (DC-2, DC-3, DC-4, DC-5, and DC-6)
are all located at more than a half mile from shore. The choice of a half
mile as the critical distance follows an inflection point in zooplankton
numbers there and appears to give reasonably homogeneous groups.
Means and standard errors have been computed using the above groups. The
results are given in Table 3 and are plotted in Figure 2. In most of the
months studied the mean abundance was lower in the offshore stations; aside
from this the abundance data seem to be essentially random. No repeating
typical seasonal pattern is evident.
In July 1972 the Utermohl method of phytoplankton analysis was replaced
with the Settle-Freeze method of Sanford, Sands, and Goldman (1969) (see
Ayers and Seibel 1973 for a discussion of the reasons). Because of the
method change the abundance data of 1972 have not been subjected to statistical
testing. The data for 1973 are counts by two different analysts of greatly
different experience and have not been tested. The 1974 abundance data are
all the work of one analyst and have been considered strong enough for testing.
Application of the Student's-t test to the 1974 data shows the inshore-offshore
abundance differences to be insignificant.
The grand mean of the abundance data from the inshore stations for all
months for 1972 through 1974 is 1631 cells per ml. This can be a preoperational reference value to which postoperational data can be compared.
There is no clearly defined progressive increase in the abundance of
phytoplankton in the Cook Plant region over the years 1972 through 1974. At
present it is not possible to give a clear-cut reason for the increase in
numbers of "abundant" forms, other than increased skill of the analysts. In

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