The Effect of CuSO₄ and Exposure Time on Chlamydomonas reinhardtii Population

Abstract

Chlamydomonas reinhardtii, a green algae, is one of many critical primary producers, making up the base of most aquatic food webs (Norambuena et al. 2-6). Any disruption to its populations, can in turn, affect other inhabitants of that ecosystem, including salmon (Müller-Navarra and Dörthe 489-505.). Copper acts as an essential compound when present in small quantities for many species, but becomes highly toxic past one’s biological requirements (Gaetke et al. 147-163). This study aims to understand the impacts of different concentrations of copper sulfate and exposure time on a population of C. reinhardtii. It is predicted that the population of C. reinhardtii will be affected by exposure time and CuSO₄, respectively, and that there will be an interaction between time and copper concentration on the population. This was achieved by subjecting a population of C. reinhardtii to three separate treatments of CuSO₄ over time: a control of 0 μM, 100 μM, and 200 μM CuSO₄. By assessing the results obtained through similar studies in the literature, the following concentrations were chosen to best describe both a lower and a higher limit for the copper tolerance of C. reinhardtii. The study was conducted over an 11 day period, with a total of 8 sampling days. Through the use of a haemocytometer, cell counts for each treatment group were recorded approximately every 24 hours, and the samples were kept in an incubator between data collections. The data was analyzed using a two-way ANOVA test, which resulted in p-values of 3.68E-13, 1.63E-30, and 1.34E-19. Since the obtained p-values were smaller than α of 0.05, the three null hypotheses were rejected. This suggests that the individual factors of copper sulfate concentration and exposure time, as well as their interaction, affect C. reinhardtii population. While the impact of the 100 μM CuSO₄ treatment group was very similar to that of the 200 μM group, there was a significant decline in population between the control and these two treatment groups. As such, the further study of exact copper tolerance ranges is crucial in understanding how its anthropogenic input into aquatic systems, whether through mining activities, pesticide run-off or others, would affect the ecosystem (Willis and Bishop 37).