Differential Effects of Growth and Loss Processes in Controlling Natural Phytoplankton Populations

摘要

An investigation was made of factors controlling algal succession in a small, oligotrophic lake during summer stratification. Weekly measurements were made of growth rate, sedimentation rate, and population density for each of the dominant phytoplankton species. Weekly diel measurements were made of zooplankton grazing rates using exp 14 C labeled algae. Cyclotella michiganiana was the dominant algae through the end of June at which time Cyclotella comensis began to increase, becoming the dominant by August. In August, high grazing pressure caused the rapid declines of both C. michiganiana and C. comensis which were followed by an increase of Sphaerocystis Schroeteri. The combined effect of greater growth rates and lower loss rates of C. comensis resulted in its dominance over of C. michiganiana. In contrast, the C. comensis - S. Schroeteri succession clearly resulted from differential mortality alone. It is likely that the importance of losses due to sedimentation and/or grazing is large in many lakes and that interspecific competition may be less important in actually controlling seasonal succession. (ERA citation 81:026208)