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

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Environmental Parameters Treated Individually
Depth: The samples of Pontoporeia were pooled into 10 m depth
increments. The shallowest depth interval included all observations
between 9 and 15 m and was designated the 10 m increment. The next
depth interval, including all observations between 16 and 25 m, was the
20 m increment, and so forth. An inspection of Figures 31 and 32 shows
that the maximum density of Pontoporeia occurred around the 30 m. On
the average, there were fewer individuals at the 10 and 20 m than at
30 m and the confidence intervals show considerably more variability at
these two depths than at any of the others. There is a sharp decline of
amphipods from 30 to 40 m, then a leveling off from 40 to 50 m with
another sharp decline from 50 to 60 m. They gradually decrease from
60 to 230 m, beyond which the density is fairly uniform. The correlation coefficient showed this same relationship.
Time: All observations of the three sampling seasons were combined into monthly intervals for Pontoporeia and no sighnificant monthly
variation in abundance was found (Fig. 33). Figure 34 likewise indicates
no significant correlation between average number of Pontoporeia per
station stop and day of the year.
Bottom Temperature: The samples of Pontoporeia were pooled
with respect to bottom temperature increments consisting of 1~C intervals. The 1~ interval included all observations between 0. 6 and 1.5 C
while the 20 increment contained all observations between 1.6 and 2. 5~C