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

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ence in abundance was found among the four depth zones; the density
of numbers was greatest in the 36-65 m zone followed, in order of decreasing abundance, by the 10-35 m, 65-105 m, and greater than 105 m
zone.
Pooled amphipod counts of the four depth zones were again treated
with the Kruskal-Wallis rank test to determine if the standing crop of
a:mphipods were significantly different for the three sampling periods.
This test showed no apparent difference in the standing crop for the
10-35 m, 36-65 m, and greater than 105 m depth zones. The grand
geometric mean number of Pontoporeia for the four depth zones of the
three sampling seasons and the results of the Kruskal-Wallis test are
presented in Table 8.
A reexamination of Figure 44 and Table 8 shows that although
there was no significant seasonal variation in the abundance of amphipods
at the 10-35 m zone there was considerable variation within comparable
sampling periods. In 1965 there was a general increase in the populaTABLE 8. The grand geometric mean number of Pontoporeia affinis
for the three sampling seasons. H represents the results of the
Kruskal-Wallis test.
JDepth Zones 1964 1965 1966 H
10-35 m 62 55 67 2.78
36-65 m 78 75 75.52
66-105 m 50 59 58 7. 76*
>105 m 35 40 36 3.81
All stations combined 53 55 54.55
*Significant at 5%