Effect of photoperiod on exponential growth rates of Chlamydomonas reinhardtii and the downstream impacts on juvenile salmon populations

  • Nick Hsieh
  • Shayan Molaei
  • Pavneet Virk
  • Shaylen Young
  • Irena Zivkovic


Chlamydomonas reinhardtii are photoautotrophic green algae. Given this characteristic, the purpose of our experiment was to determine if photoperiod has an effect on the population growth rate of C. reinhardtii. Our experiment consisted of our Control, Treatment 1, and Treatment 2, for which the algae were kept in climate controlled incubators and exposed to 8hour, 3-hour, and 21-hour photoperiods, respectively. We collected samples of cultures for all treatment replicates over a nine day period. The growth curves obtained show a trend of increasing cell concentration with increased photoperiod. Statistical analysis using one-way ANOVA on maximum growth rates and Tukey HSD test showed a significant difference between Treatment 1 and 2 maximum growth rates (p= 0.0395); as such, we rejected our null hypothesis, providing support for the alternate hypothesis that C. reinhardtii maximum growth rate changes as photoperiod changes. These results demonstrate that the exponential growth rate of C. reinhardtii is significantly higher at a 21-hour photoperiod, compared to a 3-hour photoperiod. This suggests that during spring months, when juvenile salmon emerge from the nest and photoperiod is high, increased growth rates of C. reinhardtii will be observed. This affects upper trophic levels, as zooplankton and invertebrates feed on green algae, such as C. reinhardtii; newly emerged juvenile salmon will in turn feed on the zooplankton and invertebrates. We conclude that that C. reinhardtii exponential growth rates are significantly higher at a 21-hour photoperiod compared to a 3-hour photoperiod; this poses a profound implication on the surrounding ecosystem.