How Basic Are Daphnia?

Daphnia magna are filter-feeder planktonic crustaceans. D. magna can be found in a variety of habitats, ranging from freshwater lakes to acidic swamps. However, they are very sensitive to pH changes, thriving within a slightly basic pH range of 7.9 - 8.3. Therefore, they have been used to monitor freshwater acidification. This experiment was carried out to determine how pH levels impact D. Magna growth and survival. We hypothesized that exposing D. magna to acidic pH settings would stunt their growth, which would then result in death. We tested this by artificially creating three pH environments for D. magna, consisting of pH7, pH8, and pH9. We did this by adding sodium hydroxide (NaOH) to spring water. We compared growth changes and survival rates under the three pH levels to those found in D. magna that remained in the original (control) aquatic environment from which they were sampled for a period of one week. We examined their size changes and counted their numbers under a microscope. Their dimensions were measured using a photo analyzing software called ImageJ. We found that the D. magna thrived best at a starting alkalinity of 9 (final pH 7.3) after one week of monitoring when using the pH-adjusted water from their natural habitat. Our data of the D. magna size was inconclusive because they ended up dying constantly in all environments. Overall, D. magna survival was unstable over the one week period even under control conditions, likely due to a natural acidification of the water environment over time or because of the D. magna living in the water. In a future experiment, we would like to develop a more controlled environment where the pH is kept constant over time, and the starting age of the sampled D. magna under the different conditions tested is equal. It would also be important to analyze how the organisms would be influenced generationally under the same settings.