The seasonal biological surveys of 1971 / John C. Ayers, Samuel C. Mozley, John A. Stewart.

TABLE 11. Percentages of Tubificidae which were mature in
surveys of 1970 and 1971. Only species which lacked hair
chaetae and could not be identified in the immature stages
are included. * insufficient specimens (<50).
- Benthic depth zone
0 1 2 3
July 1970 * 55 65 86
November 1970 11 42 22 22
April 1971 40 23 29 27
July 1971 55 72 74 67
November 1971 * 3 2 5

cycles. There is only some indication of intensified reproductive activity
in summer and autumn.
DISCUSSION
These first five surveys have revealed several important facts about
benthic communities in Lake Michigan adjacent to the Cook Plant, facts which
are relevent to interpretation of apparent operational effects in years to
come. Many of them were unknown or inadequately understood prior to these
surveys. Other results merely confirm information derived from previous
studies in Lake Michigan or in other Great Lakes. This latter information
includes a tendency ofr increases in abundance with increasing depth near
shore and the overall taxonomic composition in the deeper zones. The first
area of new information is the difference between benthic zone 0, or depths
less than 8 m, and deeper zones. The zoobenthos is dominated by Chironomidae
of several species, and more typical Great Lakes species are rare, such as
Pontoporeia affinis, various Tubificidae and Pisidiumn spp. Total macro2
benthos numbers per m are very low in relation to numbers in deeper zones.
Seasonal changes in the character of the fauna are large, especially in midsummer. Small Chironomidae larvae and possibly certain Naididae become
common in summer, but are absent or very rare in other seasons. While some
of the Chironomidae in zone 0 are also common in deeper zones, a few kinds of
larvae occur primarily in this zone (Paracladopelma nereis and Parachironomus
ctr. demeijerei. This is the zone into which the Cook Plant will discharge

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