Monday, June 4, 2007 - 2:00 PM
19

Ontogenetic changes in elemental ratios and growth rates of Caenis spp. (Ephemeroptera: Caenidae) in response to phosphorus enrichment

Jason M. Taylor, Jeff A. Back, Ryan S. King, Kari L. Fallert, and Emily Hintzen. Department of Biology, Center for Reservoir and Aquatic Systems Research, Baylor University, One Bear Place #97266, Waco, TX 76798-7266

We contrasted the carbon, nitrogen, and phosphorus (C:N:P) stoichiometry of Caenis spp. (Ephemeroptera:Caenidae) nymphs from 2 stream reaches differing in P enrichment.  We also estimated growth rates of nymphs reared on periphyton of different P content in a laboratory experiment. Stoichiometric comparisons from the field and laboratory growth rate estimates were analyzed across nymphal development classes.  C:N ratios of field-collected nymphs increased with developmental class whereas C:P and N:P ratios increased from classes 2-4 and then declined sharply in class 5 at both sites.  C:P was lower at the highly enriched site for all but one development class.  Growth rates generally increased in response to P enrichment, but this growth response diminished in later development classes resulting in a significant interaction between P treatments and development classes.  Trends in field data imply that later stages of development have higher N and P requirements than earlier classes and nutrient enrichment may affect sequestration of P by nymphs.  Laboratory data suggest that early development classes are more P limited but in light of field results, nymphs may shift P allocation from somatic growth to reproductive development as organisms mature. 

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