Variations in the Physiological State of Size-Fractionated Plankton and their Relations with Environmental Parameters in Hypertrophic Lake Barato

Abstract

Variations in the physiological state of planktonic assemblages were studied twice in hypertrophic and shallow Lake Barato. The adenylate energy charge (AEC) and adenylate concentration were applied as indicators of the physiological state of a plankton community. AEC value and adenylate concentration in three fractions (> 100μm, 100 to 2μm, 2 to 0.2μm) fluctuated markedly, but the variations did not synchronize. AEC values significantly varied during the observation over 24 hr. AEC varied from 0.51 to 0.65 for the large fraction, > 100μm, from 0.30 to 0.71 for the medium fraction, 100 to 2μm, and from 0.31 to 0.74 for the small fraction, 2 to 0.2μm, in June 1986. In August 1986, they ranged from 0.47 to 0.72 for > 100μm, 0.55 to 0.75 for 100 to 2μm, and 0.43 to 0.77 for 2 to 0.2μm. These values ranged from " in a high active state " to " in a low active state " (CHAPMAN, 1977). Other factors detected in the lake water might influence variations in the physiological state of planktonic assemblages in L. Barato. A relatively high correlation was found between the AEC values of planktonic assemblages of the 100 to 2μm and 2 to 0.2μm fractions and concentration of dissolved proteins (D-Pro) and dissolved sugars (D-Su). It is suggested that a microbial community of the 2 to 0.2μm fraction is affected through the excretion of D-Pro and D-Su which increased with the activity of plankton of 100 to 2μm. This indicates that the physiological state of microorganisms in the 2 to 0.2μm fraction may depend on that of planktonic organisms larger than 2μm, probably through the release of organic matter.