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

components-cyclopoids, diaptomids, and Bosminidae patterns can be seen.
Bosmina was most abundant at the inshore stations, at some of which it
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exceeded 100,000/m and comprised over 80% of the crustaceans collected.
Both Diaptomus and Cyclops were taken in greatest numbers at the offshore
stations.
Of the Diaptomus species, D. minutus was most abundant, while among the
cyclopoids, only Cyclops bicuspidatus thomasi was common. We found the other
principal cyclopoid, Tropocyclops prasinus mexicanus, in small numbers. Signs
of reproductive activity were noted in Cyclops, Tropocyclops, Diaptomus
ashlandi, D. minutus, and D. oregonensis. Limnocalanus was present at the
deeper stations and a few Eurytemora affinis were found in most samples, but
Epischura Zacustris was absent from all stations visited in this survey.
Aside from Bosmina, the only other abundant cladoceran was the large
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preditor, Polyphemus pediculus, whose numbers averaged 240/m. We found
roughly equal numbers of the large predaceous rotifer, Asplanchna, at the in3
shore and the offshore stations —ca. 1800/m.
The Survey of 2 September 1971
Zooplankton counts averaged 70,000/m3 in September, 40% higher than September of 1972. Inshore-offshore differences were pronounced on this date,
with all copepod species more abundant at the deeper stations and most of the
cladoceran species more abundant inshore.
As in 1972, immature cyclopoid and calanoid copepods were a substantial
part of the September fauna. They outnumbered adults by more than 5 to 1.
Among the cyclopoids, Tropocyclops was nearly as abundant as Cyclops on this
date (ca. 2000/m3); and of the diaptomid adults, D. ashZandi was again (as in
April) the most common species. Both D. ashlandi and D. oregonensis were reduced in abundance inshore, but this does not appear to have been true for D.
minutus. The hypolimnetic species D. sicilis and LimnocaZanus were absent
from the survey area during September —possibly the result of a deepened
thermocline. Highest numbers of Eurytemora (ca. 25/m ) and Epischura (ca.
70/m3) were recorded on this date.
The September collections were most notable for their richness in cladocera. Bosmina abundances averaged 15,000/m, a reduction from averages of
57,000/m3 in July but not the striking crash seen in 1972. Around 700

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