The effect of nutrition on the response of field populations of the calanoid copepod Acartia tonsa to copper

Continuous flow toxicity tests were conducted on field populations of adult Acartia tonsa collected from Narragansett Bay. Potential algal food at the collection site was estimated from ATP and chlorophyll analysis. There was positive correlation (P < 0.01) between chlorophyll a and ATP. Integration of these data with quantitative zooplankton analysis established that A. tonsa had a significant grazing effect on algal biomass (P < 0.05). The natural population dynamics of A. tonsa during this period were assessed from microscopic analysis of tow material.The sensitivity of A. tonsa to total copper ranged from 9.0 to 78.0 μg l⁻¹ for 72 h LC50's. Results show an inverse correlation (P < 0.05) between the log LC50 and adult A. tonsa density at the time of collection. The relationship between A. tonsa sensitivity to copper and the food ration (algal density/A. tonsa density) has been described by a quadratic function which has a correlation coefficient of 0.78. This indicates that the log LC50 increases with increasing food ration up to a point and then remains constant. A comparison of confidence intervals about the LC50's indicates greater variability in the response of field animals compared to previous studies with cultured populations. This data suggests that field populations of A. tonsa can be expected to exhibit a wide range of sensitivity to other pollutants. Sensitivity is strongly correlated with population density and food ration.