Aquatic Sciences Meeting, Albuquerque 2001

SS19 Revisiting Redfield: C:N:P Stoichiometry in Aquatic Ecosystems (Disciplinary Connections)

Date: Tuesday, February 13, 2001, Time: 2:30:00 PM

Location: Acoma/Zuni/Tesuque

DeMott, W, R, Indiana-Purdue University, Fort Wayne, USA, demott@ipfw.edu

Tessier, A, J, Kellogg Biological Station, Hickory Corners, USA, tessier@kbs.msu.edu

TESTING MECHANISMS OF FOOD QUALITY LIMITATION OF ZOOPLANKTON GROWTH

We used growth assays with natural seston, measurements of P balance and feeding experiments to test mechanisms of Daphnia food limitation in three eutrophic Dutch lakes and six oligotrophic Michigan lakes. Improved growth and increased P-content in response to P supplementation confirmed P limitation of native Daphnia in the Dutch lakes. However, addition of Synechococcus, a readily assimilated cyanobacterium, improved growth beyond that achieved by P addition alone. Despite similar seston concentrations, Daphnia growth in seston from three deep Michigan lakes (mean 0.14/d) was much lower than in seston from three shallow lakes (0.33/d). Daphnia from the deep lakes exhibited weak responses to P and fatty acid additions, intermediate responses to a P-deficient alga and strong responses to Synechococcus. Higher P assimilation efficiency in shallow lakes (mean 43%) than in deep lakes (20%) showed that digestion resistance can account for the growth differences between lakes. Deviations from P homeostasis further suggest that Daphnia were on the edge of P deficiency. Understanding zooplankton food limitation in nature will require simultaneous testing for energy limitation and nutritional deficiencies.

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Aquatic Sciences Meeting, Albuquerque 2001

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