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

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from year to year. However, Eggleton had only 167 samples, collected
over a two year period, available for his analysis while more than 1, 700
samples were collected in the three years of the present study. Further,
his 1932 samples were from a different region of the lake than those taken
in 1931.
Henson (1954), in an investigation of a single produndal station in
Cayuga Lake that was approximately 100 m deep, reported that in 1952
there was a significant increase in the total crop of Pontoporeia occurring
from May to October. He found that the 1953 standing crop was significantly greater than that in 1952. He attributed the 1953 increase to the
production of young and the immigration of amphipods from the shallower
depths.
Although there was no significant seasonal variation in the abundance
of amphipods at the 10-35 m zone in Lake Michigan there was considerable
variation within sampling seasons. The numerical decrease from March
to April 1966 represents the death of spent females. The low density of
amphipods in the late spring and early summer is probably attributable
to losses arising from the elutriation- screening device that separates the
organisms from the sediment. Large numbers of newly released amphipods may have been swept through the separating screen, As the small
amphipods increased in size, they were less inclined to be lost in this
manner. The remaining three depth zones do not appear to show any
well defined patterns within the sampling periods.