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

life phase of Chironomidae lasts only a few days, these larvae must be in the
lake at all seasons, Probably they are too small to be retained in the
sieves or are in diapause in egg or early larval stages except for seasons
in which they appeared in the samples.
Figure 9 shows the patterns of two of the most numerous kinds of zoobenthos in the survey area, Pontoporeia affinis, the amphipod, and the aquatic
worm Stylodrilus heringianus. Both increased greatly in number with increasing depth, and largely determined the pattern shown by total macrobenthos. P.
affinis was more numerous in July than in April or November of the same year,
and means in July and November 1971 were greater than those in the same months
of 1970 in zone 3. These differences were not statistically significant however. S. heringianus was also more abundant in 1971 than in 1970 and again
primarily in benthic zone 3. S. heringianus was essentially absent from
depths less than 16 m (benthic zones 0 and 1) while P. affinis was numerous
in benthic zone 1 only in July of both years.
Figure 10 shows the bathymetric and seasonal patterns for the other two
numerically dominating taxa, the fingernail clams of the genus Pisidium
(several species) and the diverse aquatic worms of the family Tubificidae.
The only obvious generalization is that neither taxon is very numerous in
samples from benthic zone 0. Pisidium spp. were most abundant in benthic
zone 3 except in July 1970, when sample-picking procedures for the benthos
surveys had not been completely standardized. It is possible that very small
Pisidiwn (probably P. conventus) which are very abundant in deeper samples
were overlooked in that first month. The most numerous identifiable Tubificidae were Limnodridus hoffmeisteri, PeZoscolex freyi and Potamothrix moldaviensis in most samples (see Appendix D), but Tubifex tubifex, other Limnodritus species and occasionally Potomothrix moldaviensis or AuZodriZus
americanus contributed substantially to the total numbers for this family.
Large proportions of the Tubificidae were unidentified immatures, so that it
was not possible to represent depth distribution or seasonal fluctuations of
individual species. Both means and standard errors for Tubificidae were
largest in one of the two intermediate benthic zones (zone 1 or 2) with the
exception of April. This was due to a tendency for very dense populations of
Tubificidae to occur at a few stations between 8 and 24 m on every survey
(e.g., SDC-7-3 in November 1970).

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