. Bulletin. Natural history; Natural history. 390 Illinois Natural History Survey Bulletin Vol. 32, Art. 4 I al. (1976) found Corbicula were more abundant on substrates of sand in combination with mud or detritus than they were on substrates which were predominantly mud or detritus. In Dale Hollow Reservoir, Tennessee, Abbott (1979) found highly significant differences between 8-m and 12-m depths for shell sizes and densities, with larger individuals occurring at 8 m and greater densities occurring at 12 m. Temperature differences between the 8- and 12-m depths were hypothesized as the major f
. Bulletin. Natural history; Natural history. 390 Illinois Natural History Survey Bulletin Vol. 32, Art. 4 I al. (1976) found Corbicula were more abundant on substrates of sand in combination with mud or detritus than they were on substrates which were predominantly mud or detritus. In Dale Hollow Reservoir, Tennessee, Abbott (1979) found highly significant differences between 8-m and 12-m depths for shell sizes and densities, with larger individuals occurring at 8 m and greater densities occurring at 12 m. Temperature differences between the 8- and 12-m depths were hypothesized as the major factor affecting shell size, whereas substrate type appeared to modify density. The highest densities of Corbicula in several Texas reservoirs were associated with sand-gravel substrates and boulder rubble, while the lowest densities were noted in fine sand, in sharp granite gravel, and in substrates containing a high percentage of clay and sih (O'Kane 1976). Eng (1979) reported densities in sediment bars of the concrete- lined Delta-Mendota Canal, California, of 10,000-20,000 clams/m2. During the summer of 1975, the mean density of clams in the littoral zone (1-3 m depth) was higher in all areas of the cooling loop (except the discharge canal) than it was in the control arm (Fig. 6). The highest average clam population in the littoral zone was found within the intake canal (*). In other areas of the cooling loop average concentrations decreased gradually from 50 clams/m^ in the discharge arm to 25 clams/m^ in the intake arm south. The average density in the control arm littoral zone was at least three times lower at 8 clams/m^, which suggested that the population in the cool- ing loop benefited from power plant operations that supplied heat and/or cur- rent. The lowest clam density in the lit- toral zone was in the discharge canal (4 clams/m^). That low population was attributed to the clam die-off during the summer of 1975 as a result of 40''C water temperatures. In cont
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