Ecology of the burrowing amphipod, Pontoporeia affinis, in Lake Michigan / by Wayne Paul Alley.

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tion from April to August followed by a slight decline from August to
November. The 1966 population decreased in numbers from March to
April., increased from April to August, and then decreased sharply
from August to November.
A Spearman rank correlation coefficient was computed for the
four depth zones and for all depths combined to determine if any association patterns of Pontoporeia abundance existed among the three
sampling seasons (Table 9). The results indicated no correlation in
the seasonal patterns of abundance for any of the four depth zones.
Only the 10-35 and 36-65 m zones showed any association when all the
stations were combined.
Figure 45 shows the patterns of seasonal abundance of Pontoporeia
for the seven stations of the C transect. The Kruskal-Wallis test
indicated that only at station C-3 was the average standing crop significantly different for the three sampling seasons; there appeared to be
no seasonal differences at the other C stations. The grand mean number
of amphipods for these 7 stations for the three sampling seasons and
the results of the Kruskal-Wallis test are presented in Table 10.
Figure 45 indicates that the patterns of amphipod abundance for
1965 and 1966 are quite similar for stations C-2, C-3, C-6, and C-7,
and changes in amphipod counts of stations C-4 and C-5 were similar
in many respects. The seasonal changes at station C-l, however,
differ strongly from the other six stations.