POPULATION RESPONSES OF THE FRESH-WATER AMPHIPOD CRUSTACEAN GAMMARUS-PULEX (L) TO COPPER

1. Populations of Gammarus pulex (density 4000 m-2) were exposed, over a 100-day period in a continuous-flow dosing system, to concentrations of copper below the 240 h median lethal concentration (LC50) for juveniles. 2. There was a significant effect of copper on the resulting population density. In the control and lowest treatment (11.0-mu-g l-1) it was double the initial density, but with increasing copper concentration there was a decrease in density until at the highest treatment (23.1-mu-g l-1), it was less than that of the initial population. The lowest observed effect concentration (LOEC) for population density was 14.6-mu-g l-1. 3. Copper significantly affected the age composition of the final populations. In the control and lowest treatment concentration, the population was composed mainly of juvenile animals. With increasing copper concentration, however, there was a decrease in the number of juveniles, the LOEC being 14.6-mu-g l-1. The number of adults in the final population was also significantly reduced by copper, with an LOEC of 18.2-mu-g l-1. 4. The relationship between the body length and number of antennal segments of animals in the populations at each treatment concentration showed that growth was impaired by increased copper concentrations.