Tolerance of marine calanoid resting eggs: Effects of freezing,desiccation and Rotenone exposure - a field and laboratory study

Tolerance of calanoid resting eggs from bottom sediment in a manipulated marine enclosure (Svartatjønn, western Norway) to freezing, desiccation and exposure to the insecticide Rotenone was examined in 1989 and 1990, both in situ and in the laboratory. Egg abundances in the sediment were compared before and after draining followed by Rotenone treatment. The drained parts of the basin were exposed to both drying and freezing. A significant decrease in hatching success was found in the drained parts during the study (p<0.05,t-test) and in the deepest parts, which were exposed to Rotenone. No significant difference was found in an intermediate zone around the new water level established by the draining. Both drying (at 20°C) and freezing (at –15°C) caused total mortality of the eggs in laboratory experiments. Laboratory experiments also showed that Rotenone concentrations higher than 0.5 ppm resulted in significantly reduced hatching rates, indicating that resting eggs of calanoids tolerate 20 to 100 times higher Rotenone concentrations than do later ontogenetic stages. The operational procedure (i.e. draining and Rotenone treatment) employed in enclosed ponds used for marine fish fry production will, within a 1-yr cycle, reduce the abundance of resting eggs and therefore the potential for self-recruitment of the zooplankton stocks.