The species-specific responses of natural phytoplankton communities to low cadmium concentrations were measured in Lake 239 (Experimental Lakes Area, northwestern Ontario). Both in situ and laboratory 5-L continuous-flow cultures, and 5-L and 100-mL cultures were used. Asterionella formosa, Dinobryon sertularia, and Dinobryon bavaricum showed dramatic negative sensitivity to low cadmium concentrations (5–100 μg/L), while Rhabdoderma gorskii and Elakatothrix sp. consistently increased in numbers at the same cadmium concentrations. In all experiments, some species exhibited no apparent effect to cadmium addition as measured by cell counts. The "bottle effect" of each technique was evaluated by comparing the community similarity valves of the control cultures to the lake samples and showed the in situ continuous cultures to be most similar to the lake followed by the laboratory continuous cultures, the in situ 5-L batch cultures, the 5-L laboratory cultures, and the 100-mL batch cultures. Replicate cadmium cultures, all techniques, were more similar to each other than the lake samples. The similarity of the cadmium cultures to the lake sample or control cultures decreased with increased cadmium concentration and incubation time.
Maintenance of Intraspecific Diversity in Response to Species Competition and Nutrient Fluctuations
