Effects of temperature and nutritional state on the toxicity of acridine to the Calanoid Copepod Diaptomus clavipes Schacht

In acute bioassays, LC50's were used to estimate median lethal concentrations. Ninety-six hour LC50's for adult Diaptomus clavipes ranged from 2.36-6.43 mg/1 depending upon temperature and nutritional state of the animals. LC50's were highest for well-fed animals at 16° C. As food availability decreased, sensitivity to acridine increased as temperature increased. No differences in LC50's were found between the sexes except in starved animals at 26°C. Males were more sensitive than females. Acute bioassays on immature stages (NI-CI) were more sensitive than the adult stage, with LC50's ranging from 1.18-1.7S mg/1 for the three temperatures.

As acridine concentration increased, duration of immature stages increased and adult size decreased. These two variables were most sensitive to toxicant stress at 16° C. Metasomal lengths of first stage copepodids were unaffected by acridine concentration but decreased with increasing temperature.

Three measures of reproduction (number of eggs/clutch, number of clutches/female/day, number of eggs/female/day,) were examined. These measures varied in their sensitivity depending on temperature being most sensitive at 21° C. At 21°C and 26° C, clutch size did not significantly vary among the acridine concentrations when compared to controls. At 21° C, clutch size was significantly reduced in acridine exposed animals. Rate of clutch production was a more sensitive indicator of reproductive inhibition than clutch size at all temperatures. Rate of egg production which utilizes information on clutch size and clutch production yielded results similar, to the rate of clutch production.

Acute and chronic bioassays revealed that Diaptomus clavipes was more sensitive than Daphnia magna except for the adult acute test where Diaptomus clavipes was more tolerant. This was probably due to cessation of molting in mature Diaptomus clavipes.