Joint variation of zooplankton and seston stoichiometry in lakes and reservoirs

Summary We tested several stoichiometric hypotheses for thejoint dependence in element ratios in zooplanktonand their resources using direct chemical measure-ments of zooplankton (>80 µm) and seston. Our fivefield sites included three small boreal lakes, a warmwater reservoir and Lake Superior. Zooplankton ele-ment pools were generally not large compared to thetotal seston. We found a tight homeostasis in bulkzooplankton element ratios compared to theirresources. Weak correlations consistent with stoichi-ometric hypotheses were seen. Zooplankton C:P andC:N were very slightly positively correlated withseston ratios, but the zooplankton N:P ratio wasnegatively correlated with the same ratio in theseston. Acknowledgements Financial support came from the National ScienceFoundation, NOAA, and the University of Minne-sota. Fig. 3. Expansion of the vertical scale of Fig. 2A.Horizontal dotted lines indicate reported values ofC:P for a high and a low C:P zooplankton taxon(from S TERNER et al. 1992). The wavy line is a dis-tance-weighted least squares regression. The solidinclined line represents an hypothetical region ofexclusion (high seston C:P precludes dominance bylow C:P zooplankton).