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e <br />organisms. Hanf (1982) reported plankton densities of 10-4,702/m3 on the Columbia <br />River and Holden and Green (1960) reported maximum densities of 10,200/m3 on the <br />Sokoto River. Saunders and Lewis (1988a, 1988b, 1989) have reported river densities <br />of 510-4,760\m3 in Venezuela rivers. River densities in our study aze in agreement <br />with these studies. <br />FlDOdDlain. Floodplain plankton densities ranged from 205,923/m3 at high water <br />to 690,187lm3 at low water. The water level within the floodplain decreased one <br />meter during the sampling period. This would have decreased total water volume by <br />approximately one half. The increase in plankton densities was probably caused by the <br />concentrating affect of the decreasing water volume. Other studies have found that <br />high densities associated with decreased water levels in floodplain lakes do not <br />necessarily correspond to larger population sizes, although densities may increase <br />dramatically as reported in this study (Twombly and Lewis 1987, Crome and <br />Carpenter 1988). Benthic densities ranged from 262,808/m2 in June to 85,812/m2 in <br />August. The benthic density was higher than the plankton density during the first <br />sample period. <br />Maximum densities of zooplankton in floodplains as summarized by Welcomme <br />(1979) range from 270,000-10,000,000/m3 (counted organisms not known). Twombly <br />and Lewis (1987) report mean densities of abundant species of cladocerans and <br />copepods in Laguna la Orsinera along the Orinoco River, Venezuela of 420,800/m3. <br />Floodplain densities in our study would be lower than those found by Twombly and <br />Lewis had we only included abundant species and excluded naupliaz stages. Nauplii <br />16 <br />