Effects of increased water temperature on Daphnia pulex
Effects of increased water temperature on Daphnia pulex Techniques were developed to study the effects of increased water temperature on certain zooplankters; specific studies were conducted on Daphnia pulex, an abundant and important zooplankter of the lower Columbia River. Study methods simulated prolonged exposure to constant high temperatures in thermal discharges and short exposures to increased temperatures in condensers of cooling systems. Effects were evaluated on the basis of survival and reproduction for periods ranging from 34 to 90 days. The time to death of 50 percent of the D. pulex, both mature and young, was less than 24 h at temperatures above 27/sup 0/C. Temperatures of 27/sup 0/C and below required an exposure of at least 192 h to cause 50 percent mortality. The young females were more tolerant of temperature increases than older females. The greatest reproduction by older females was at the control temperature (15/sup 0/C), whereas reproduction by the young females was low at lower temperatures. No reproduction occurred above 27/sup 0/C. Two groups of D. pulex (one from the Seattle, Wash., area and the other from the Columbia River) studied at increased temperatures for prolonged periods revealed similar patterns of survival and reproduction, but the Columbia River group appeared less tolerant of increased more »
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