CS39A Zooplankton - Feeding, Reproduction, Growth and Molecular Diversity
Date: Tuesday, June 11, 2002
Time: 11:30:00 AM
Location: View Royal
 
DeMott, W, R, Indiana-Purdue University, Fort Wayne, USA, demott@ipfw.edu
EdingtonJR, Indiana-Purdue University, Fort Wayne, USA, finallyconnected@hotmail.com
Tessier, A, J, Michigan State University, Hickory Corners, USA, tessier@kbs.msu.edu
 
TESTING ZOOPLANKTON FOOD LIMITATION ACROSS GRADIENTS OF DEPTH AND PRODUCTIVITY IN SMALL STRATIFIED LAKES
image
We used Daphnia juvenile growth assays to test the intensity and mechanisms of food limitation during summer in four depth strata of four lakes that differ in productivity. We also sampled resources (chlorophyll, particulate C and P) and the day/night depth distributions of Daphnia spp. The growth assays included treatments with natural seston and seston supplemented with phosphate or Synechococcus, a P-rich cyanobacterium highly deficient in sterols and essential fatty acids. Our results provide evidence for strong energy limitation and weak P-limitation in upper layers. Growth was very high with resources from a deep layer of sulfur bacteria that was protected from grazing by low oxygen. Strong positive responses to Synechococcus supplements and high growth with sulfur bacteria are both contrary to limitation by essential lipids. Across depths and lakes, strong food limitation was Daphnia density dependent, and was associated with community grazing exceeding about 20% per day.