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and a corresponding increase in dead rotifers was not noted. This may be explained by predation
(many large calanoid copepods were present) or settling in ballast tanks of dead individuals.
Therefore, although there was no significant difference among treatments during the fill or
during the discharge, there was a significant difference associated with holding time (p = 0.005)
for the May 12 trial.
Figure 2. Zooplankton abundance and percent dead among validation trials. Note: Percent dead
observed in T1 and T2 for the Y-fill sample port was zero.
The results show that phytoplankton abundances were more variable than zooplankton
from the same samples. This is not surprising given the smaller sizes, higher natural
concentrations, and natural patchiness of phytoplankton. While some significant differences
were found between C and T lines upon filling of ballast water (May 12 p = 0.256, May 13 p =
0.011, May 14 p = 0.040), it is important to note that no significant differences between the
concentrations of phytoplankton were found in the discharge water from the C and T tanks for
all three trials (May 12 p = 0.953, May 13 p = 0.242, May 14 p = 0.853). Over the 3 days of
testing, there was also an increase in ambient phytoplankton concentrations. This was mostly
due to a bloom of a very common spring bloomer
Prorocentrum minimum
. During the
validation testing period, dinoflagellates (mostly
P. minimum
) also increased from 300-400/ml