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

CONCLUSIONS

This amphipod, Pontoporeia affinis, is a remarkable organism.
The field observations of this study indicate that Pontoporeia is capable
of enduring a wide range of environmental conditions. In Lake Michigan,
it is found from the sublittoral to the deepest profundal areas and tolerates
water temperatures that range from 1~ to 19~ centigrade. Although
Pontoporeia is a burrowing amphipod it is also found, in low densities,
within hard bottom surficial sediments, Juday and Birge (1927), in an
investigation of Green Lake, Wis,, found that Pontoporeia was able to
survive within the sediments when the water contained 0, 72 cc/1 dissolved oxygen one meter above the bottom.
The results of this study strongly indicate that Lake Michigan cannot be treated as a unit in the analysis of the interrelationships of
Pontoporeia and its environment. This amphipod has the extraordinary
capability of adjusting to the ambient environmental. conditions and has
even adapted its reproductive cycles to comply with these local conditions.
Within the sublittoral regions of the lake, Pontoporeia has developed
two distinct reproductive patterns that appear to be related to the water
temperature. It matures in one year in the warm shallow inshore regions
of the sublittoral and requires two years to mature in the deeper portions
of this zone. Pontoporeia of the sublittoral are geared for a late winter

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