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Section 779.20 (c) Continued. <br />• in the reservoir probably account for the difference in densities. <br />Diversity indices compared very closely between the 1975 and 1979 <br />studies, as diversity in 1975 was 1.3 while in 197S it was 1.4. <br />Number of taxa, density and diversity of aquatic macro invertebrates <br />in upper Foidel Creek compare closely with crhat was found in July, <br />1975 baseline studies indicating that little change in upper Foidel <br />Creek has occurred over the past four years. <br />Mid31e Foidel Creek. Samples from middle Foidel Creek contained <br />more taxa than any of the other stations sampled. As shown in Table <br />65, Density, Percent Relative Abundance, Ddiversity and Equitability <br />of Aquatic Macroinvertebrates Collected From Middle Foidel Creek, <br />a total of .l5 taxa each were collected by Surber and ]Ekman grab. <br />Mean total density for SL~.rber samples was 54.5 organisms/ft2 while <br />the Ekman grab samples contained 75.0 organisms/ft2. Predaceous <br />diving beetles were the. most abundant g*oup in the Surber samples <br />• representing 32.1 percent of the total mean density or 17.5 organisms/ <br />ft2. Blackfly Larvae (Diptera: Simulidae) were also relatively <br />abundant and represented 27.5 percent of the total mean density or <br />15 organisms/f t2. The midge Micropsectra sp. comprised 10.1 per- <br />cent of the total mean density of the Surber samples, while tubi- <br />ficid worms comprised 7.3 percent. <br />As a group, chironomid midges dominated the Ekman grab samples <br />collected at the middle Foidel Creek Station. They comprised 37.4 <br />percent of the mean total density or 28 ogranisms/ft2. Of the <br />chironomids, Micropsectra sp. was most abundant (14.7 percent total <br />relative abundance). A relatively high number of empty caddisfly <br />{Trichoptera) larval and pupal cases were found in the Ekman grab <br />sample. The cases were probably washed into the pools where they <br />settled. Presence of only empty cases indicated that emergence of <br />caddisflies in this reach of the stream had occurred prior to the <br />July sampling, and that the next generation was either still in the <br />• egg stage or at a very early instar stage, Tubificid worms were <br />779-225 <br />