Aquatic Sciences Meeting, Albuquerque 2001

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

Date: Tuesday, February 13, 2001, Time: 4:45:00 PM

Location: Acoma/Zuni/Tesuque

Gaedke, U, , University Potsdam, Potsdam, Germany, Gaedke@rz.uni-potsdam.de

Hochstädter, S, , University of Potsdam, Potsdam, Germany, hochstae@rz.uni-potsdam.de

Straile, D, , University of Konstanz, Konstanz, Germany, dietmar.straile@uni-konstanz.de

THE INTERPLAY BETWEEN LIMITATION BY FOOD QUANTITY AND QUALITY IN FOOD WEBS. A CASE STUDY BASED ON MASS BALANCED FLUX MODELS

We established seasonally resolved flux models of the pelagic food web of large Lake Constance, which were mass balanced simultaneously in carbon and phosphorus. P was taken as surrogate of food quality as summer algal C:P ratios exceeded the threshold above which stoichiometric theory predicts P limitation of herbivores. This multiple currency model enabled to evaluate the dualism in the function of zooplankton as P sink and source and a balanced representation of energetic and stoichiometric constraints. We found no singly, strongly limiting factor but a mutual dependence of the energy and nutrient deficiency for predominantly herbivorous consumers. Their C demands were largely met by phytoplankton whereas P was mostly obtained from bacteria and their predators. This favored the occurrence of omnivores, i. e. organisms that minimized P deficiencies at the cost of enhanced energy limitation yielding colimitation by P and C of herbivores. Protozoa improved the food quality for larger consumers by repacking into larger food particles and providing a better biochemical composition. Carnivores were more important remineralizers than herbivores, which contrasts previous perceptions.

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Aquatic Sciences Meeting, Albuquerque 2001

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