Document: JAM-3-48-2

Nutrient limitation reduces food quality for zooplankton in nature: Responses of Daphnia growth to short-term amendment of phosphorus under field conditions.

ELSER, J.* ¹, K.HAYAKAWA ² and J.URABE ³

Arizona State University, Tempe, AZ 85287 USA ¹
Lake Biwa Research Institute, Otsu, Japan ²
Kyoto University, Otsu, Japan ³

Abstract:
Pelagic ecologists are increasingly recognizing from laboratory studies that the quality of nutrient-limited algae is sub-optimal as food for zooplankton production. However, little is known about food quality in nature and how quality is affected by nutrient limitation of phytoplankton in the field. To test for P-limitation of zooplankton growth in the field, we performed a set of short-term P-supplementation experiments using Daphnia dentifera as an herbivore and suspended particulate matter (seston) from three lakes at the Experimental Lakes Area (ELA) as food. In our 5-day growth experiments, neonate Daphnia fed for 6-h per day on freshly collected seston enriched (+P enrichment) or unenriched (control) with PO₄ , spending the rest of the day feeding on unaltered natural seston. Within the 6-h period, PO₄ enrichment did not affect food abundance but dramatically lowered seston C:P ratio. P-amendment of lake seston significantly stimulated Daphnia growth. The response of Daphnia growth was unrelated to concentrations and composition of fatty acids but instead seemed associated with seston P content. These results demonstrate that, even in field situations, the effects of phosphorus limitation extend beyond the algae to herbivores through reduced food quality.

Keywords: food quality, ecological stoichiometry, Daphnia

This abstract is being presented at: 1:45 PM in session:
Oral Session #47: Zooplankton Ecology.