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t r ti INVERTEBRATES Invertebrates were sampled only on 15 October. No permanent stations were established at this site. Water column invertebrate samples were taken at three different locations on the main body of the pond. A benthic sample was taken from the southwestern shoreline. In addition, three water column samples and one benthic sample were taken from the Colorado River Only two taxonomic groups, Cladocera and Copepoda, were identified in water column samples of the pond. Densities of the two groups were similar; cladoceran density was 25.9 L'1 and copepods 28.1 organisms L'1. These two taxonomic groups were also present in the river but at much lower densities; Cladocera 0.07 L'1 and copepods 0.14 L'1. The pond benthic sample produced only chironomids at a density of 68.5 L'1 or 1371 m'2. No benthic organisms were found in the sample obtained from the river. Studies by Marsh and Langhorst (1988) found that Cladocera and Copepoda were important in the diets of larval razorback suckers in a backwater of Mohave Lake. Densities of these organisms in the 29 5/8 pond are at moderate levels for this time of year. Nothing however is known of the seasonal population densities. Benthic invertebrates, consisting of chironomid larvae, also occurred at relatively moderate densities. Chironomidae, as described by Grabowski and Hiebert (1989), are important to the diet of several endangered fish. It is likely that between the two strata, water column and benthos, that sufficient populations of invertebrates occur to support larval fishes. The low invertebrate taxa richness could possibly be related to the lack of aquatic vegetation. No submerged or emergent vegetation was observed in or around the margins of the pond. The lack of vegetation creates little habitat for organisms that are not strictly pelagic such as the Chironomidae, Ephemeroptera and Odonata. The absence of vegetation in the pond also reduces the diversity of benthic habitat. Other environmental factors do not appear limiting to aquatic -invertebrate life. The four variables measured and presented in Figure 1 were all taken on the surface of the pond within six inches of the surface. Corresponding readings near the bottom were also taken and those readings were all similar to near surface measurements. This indicates that at .this time no temperature or oxygen stratification occurred. The shallow nature of the pond (5.5 feet deep) in combination with wind action likely aided in mixing the water. Water quality measurements were taken from 1440-1545 hours when oxygen levels would be high due to water column algae. 2