When we were to select our project, we selected to experiment with Daphnia magna. Daphnia are crustaceans better known as water fleas. They are aquatic animals that live anywhere water is found. Daphnia are filter-feeders that reproduce parthenogenetically.

The purpose of this experiment was to find out if exposing Daphnia magna to a salt concentration altered their average heartbeat rate. The null hypothesis to our experiment was that the average heartbeat rate of the daphnia will not change when it is exposed to a salt concentrate; that is, the heartbeat rate of daphnia will remain identical even when the environment changes.

Before we started the experiment, we concocted our solution for our experiment. First we acquired and measured out five grams of salt. We then mixed it with 500mL of tap water. When thoroughly shaken, we let the solution sit while we did our first portion of our experiment.

To acquire data for our control, we captured three daphnia from their original habitat. Then, one-by-one, we placed the daphnia on a microscope slide containing enough water so the daphnia would be fully submerged. Then, using a compound light microscope, we observed the heartbeat of the daphnia. Using a finger clicker, we counted the heartbeat rate of the daphnia for fifteen seconds, multiplied that value by four, and recorded that number in Microsoft Excel. When the daphnia was used for five trials, we returned the daphnia to its original habitat and got a new daphnia. We repeated this process using three different daphnia, doing five trials for each daphnia which resulted in fifteen data points.

Next, for testing our salt concentration, we acquired a daphnia from its original habitat and submerged it in the one-percent salt concentration. After allowing the daphnia to swim around in the solution for five minutes, we took them out of the solution and placed them under a compound light microscope. Like before, we counted the heartbeat rate using the finger clicker and recorded five trials for each daphnia, recording the data in Microsoft Excel as we went along. When we completed five trials for three different daphnia, we had a total of fifteen data points for the one-percent salt concentrate.

Finally, after we completed our data-collection process, we combined and organized all the information in one spreadsheet in Microsoft Excel and ran some descriptive statistics on them. Furthermore, we performed a two-sample f-Test for variances. Upon receiving the results, we conducted a t-Test assuming unequal variances.

The results for the descriptive statistical analysis shown in Table 2 gave us background information on the data points for the control and salt solution groups shown in Table 1. The results of the two-sample f-Test for variances (F = 0.248, df = 14, P = 0.0135) lead us to our t-Test assuming unequal variances (T = -4.017, df = 21, P = 0.0006). Because the probability was less than 0.05, we rejected our null hypothesis, concluding that the average heartbeat rate of the Daphnia in both solutions were not equal. Results show that the heartbeat rate increases in salt concentrations when compared to the control, as shown in Figure 1.

The evidence concluded states that the heartbeat rate of Daphnia increases when exposed to a salt solution. A similar experiment was conducted at the Natural Science Department at Edgewood College. They concluded that the survival rate of Daphnia decreases as the salt solution increases, and this was predicted. However, this was predicted; they wanted to know what level was safe enough for Daphnia to survive before they start dying. If the salt concentration increases up to a specific level, the Daphnia survive fine; no Daphnia died when 2.5 grams of salt was added per liter of water. However, as the concentration increased beyond that, the Daphnia started to die at a rapidly increasing rate, potentially because of over excessive heartbeat rate. This provided a point where the students knew their watershed was no longer safe (Daphnia Bioassay for Salt Toxicity).

Another experiment on the condition of Daphnia upon the exposure of salt was conducted and concluded that salt up to a specific level will strengthen the Daphnia that is exposed. However, similar to the previous experiment mentioned, this also concluded that over exposure to salt is bad for the survival of the Daphnia. When Daphnia were exposed to a specified salt solution for a period of twenty-two hours, they either died rapidly or got stronger, depending on the previous condition of the Daphnia. This is linked to the increasing heartbeat rate either being too much for the Daphnia and causing it to die, or strengthening its cardiovascular system and providing a longer life for it (Reaction of Daphnia magna).