LIFE-HISTORY, GROWTH, AND PRODUCTION OF EPHEMEROPTERA IN EXPERIMENTAL PONDS

We determined voltinism, emergence patterns, larval growth rates (instantaneous-growth method), and annual production (size-frequency method) for Caenis amica Hagen (Caenidae) and Callibaetis floridanus Banks (Baetidae) in six experimental ponds. Larvae were sampled with artificial substrates and a dip net, and adults were sampled with a light trap. Both species were bivoltine. C. amica emerged in June and july-August; C. floridanus emerged in April and September. Growth rates were 0.015 and 0.025 mg dry weight per day for the first and second generations of C. amica and 0.011 and 0.015 mg dry weight per day for the first and second generations of C. floridanus, respectively. Annual production was relatively low, 5 mg dry weight per sampler per year for C. amica and 11 mg dry weight per sampler per year for C.floridanus. The number of generations of C. floridanus and the growth and production of both species in the experimental ponds were lower than what has been reported in other studies. Some of the observed differences may have been at least partly caused by temperature (lower accumulated degree days), food (less algae), and habitat (sparse macrophytes). Our results demonstrate the usefulness and feasibility of life-history and production measurements for environmental toxicology studies conducted in large-scale model ecosystems (mesocosms).