9410

• UCREFRP Catalog Number: 9410
• Author: Wydoski, R. S. and E. J. Wick.
• Title: Ecological Value of Floodplain Habitats to Razorback Suckers in the Upper Colorado River Basin.
• USFW Year: 1998.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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1987 and 1988. Mabey and Shiozawa (1993) documented zooplankton densities
in the middle Green River as 0.3 to 1.3 organisms per liter, 1.5 to 7.1 in
the Ouray backwater, 63.4 at Intersection Wash (a large backwater), and
206 to 690 in an floodplain depression (Old Charley Wash) along the middle
Green River (Appendix 1) .

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In an open water habitat of the Moab Slough along the Colorado River
immediately upstream from Moab, Utah, the density of cladocerans and
copepods averaged about 2 per liter for backwater sites and about 36 per
liter for an open water wetland during the summer of 1993 (Appendix 2;
Cooper and Severn 1994a). Cooper and Severn did not collect any
zooplankton during their sampling from the main channel in this reach of
the Colorado River. Samples of cladocerans and copepods from the
Escalante Ranch site on the middle Green River, upstream from Jensen,
Utah, contained 0 per liter for the main river channel, a mean of 41 per
liter for backwaters, and a mean of 71 per liter for an open water wetland
(Appendix 2; Cooper and Severn 1994b). The mean number of cladocerans and
copepods from a backwater of the Gunnison River at the Escalante State
Wildlife Area, about 5 miles downstream from Delta, Colorado, was 11 per
liter and the mean number from an open water wetland was 25 per liter
(Appendix 2; Cooper and Severn 1994c). Cladocerans and copepods samples
from a floodplain depression (Old Charley Wash) in the middle Green River
on the Ouray National Wildlife Refuge contained a mean of 31 per liter in
1993 (Appendix 2; Cooper and Severn 1994d). Samples taken from the main
channel and a backwater on the refuge did not contain any cladocerans or
copepods when sampled (Appendix 2; Cooper and Severn 1994d). The density
of cladocerans was 26 per liter and the density of copepods was 28 per
liter in a gravel-pit pond along the Colorado River in October, 1993
(Appendix 2; Cooper and Severn 1994e). These studies document that the
highest zooplankton densities in the Upper Basin were in floodplain
habitats. Seasonal dynamics of zooplankton were not made in the studies
summarized above.

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The mean number of aquatic organisms captured in 5 vertical tows with a
20.3 cm plankton net in backwaters of the lower Green River in 1997 varied
between 2.4 to 124.1 organisms (combined zooplankton and free-swimming
benthic invertebrates) per liter, depending upon site and date of
collection (Table 3; Nance 1997). The mean numbers of aquatic organisms
increased in the lower Green River between May and July that corresponded
to warmer water temperatures (Table 3). The four major taxa represented
in lower Green River samples were Nemotoda, Oligochaeta, Rotifera, and
Copepoda. Several of the minor taxa included Cladocera and Chironomidae.

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Microcrustaceans that form zooplankton communities are also found in
substrates of aquatic habitats as benthos. Mabey and Shiozawa (1993)
reported between 1,000 and 6,300 benthic microcrustaceans (Cladocera,
Copepoda, and Cyclopoida) per square meter in the main channel of the
middle Green River through the Ouray National Wildlife Refuge, between
4,900 and 6,000 organisms per square meter for a backwater, 23,000 per
square meter at Intersection Wash and between 8,600 and 263,000 per square
meter in Old Charley Wash. The mean number of aquatic organisms collected
in five 1.85 cm bottom cores from backwaters in the lower Green River
varied from 65,200 to 562,200 organisms per square meter, depending upon
the site and date of collection (Nance 1997).

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C. Production of Benthic Macroinvertebrates in Various Aquatic Habitats.
Various factors affect the microdistribution and habitats of benthic
invertebrates in streams including water velocity and substrate size such
as rock, cobble, gravel, silt, and detritus (Rabeni and Minshall 1977).
The experimental results of Rabeni and Minshall (1977) are supported by

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