8067

• UCREFRP Catalog Number: 8067
• Author: Nance, E. L.
• Title: Planktonic and Benthic Invertebrate Densities in Three Backwater Habitats on the Lower Green River Final Report.
• USFW Year: 1997.
• USFW - Doc Type: Grand Junction, CO.
• Copyright Material: NO

100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
1-May

. Other
Ii Nauplii
o Copepoda
. Rotifera
. Nematoda

8-May

is-May 22-May 29-May

S-Jun

12-Jun

Figure 3: Percent composition of dominant zooplankton in Holeman canyon..

Free-living nematodes comprised 15% of the catch in the Millard Canyon samples on the
8 May sample date, but were less abundant (1-4%) or absent at other times. In contrast,
nematodes made up approximately 20% of the samples in Anderson and 25% of the
samples in Holeman. On the 08 May sample at Holeman, nematodes comprised over
50% of the average of 5 tows.

Rotifers were the only organism present in every sample and on every date and at every
site. They comprised over 50% of the total catch for the first two weeks in Millard,
dropped to an average of 20% for the next five weeks, and peaked at 86% of the average
total catch on 10 July. Except for a peak of34% on the 01 May sample in Anderson,
rotifers comprised approximately 20% of the remaining samples in both Anderson and
Holeman.

Copepod adult and copepodid life stages remained low in all sites and sample dates,
never comprising above 14% of any tow. On average, they comprised 7-10% of samples
at all three sites. Though species diversity was not determined, the dominant copepods
observed were in the suborder Cyclopoida.

In general, the naupliar copepod life stage was the dominant organism at all three sites.
Populations in Millard began with almost 40% of the organisms in the average of five
tows containing nauplii, dropping to a mere 6% on the 8 May sample, and then increasing
to 60-70% of the average of five tows in the remaining sample weeks. The drop in the 8
May sample is likely explained by their reproductive cycles. The approximate incubation
period for cyclopoid eggs ranges from 12 hours to 5 days. While many fully hatched
nauplii were not observed on this sample date, there were many hundreds of single eggs
and egg masses. Naupliar stages were more consistent in Anderson, averaging 40% of
the average of five tows at all dates. Naupliar life stages were also the dominant

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