Abstract
Daphnia magna is a species of water flea that typically inhabits freshwater ecosystems such as ponds and lakes. Because of their small size, they are susceptible to changes in their environment. To investigate how different environments affect them, we conducted an experiment with six different concentrations of vinegar: 0% (water), 0.01%, 0.1%, 1%, 5%, and 10%. After each treatment was delivered to our subject, we measured their heart rate in beats per minute. The dependent variable in this study was the heart rate of D. magna, and the independent variables were the different concentrations of vinegar. With this data, we found that the heart rate of D. magna tended to decrease as the concentration of vinegar increased. This decrease could be due to the acetic properties of vinegar which has cardiovascular benefits for individuals with accelerated heart rates.
Introduction
Pollutants, in general, have negative impacts on the environment. The impacts can include the poisoning of waterways, the creation of acid rain, and the contamination of air. In terms of aquatic life, pollutants can also be detrimental to their wellbeing. If waterways are polluted, aquatic animals and plants can be severely injured or killed. In this experiment, our independent variable was vinegar, and vinegar can be considered a pollutant to aquatic animals because it can lower the pH, causing severe impacts (World Wildlife Fund 2017).
Daphnia magna is a species of water flea that lives in freshwater areas in a wide scope of different temperatures, however they thrive in temperatures of 18-22C. Their diet consists of algae, zooplankton, phytoplankton, and other fungi. They eat through filtration, and that can be impacted by a number of factors, including water pH. Knowing this, if their water pH is lowered or raised because of pollution, it can affect their eating habits. D. magna is commonly used in smalls ponds and lakes because they can test for pollutants in the water. In addition, they are essential to the ecosystem because they are preyed upon by certain species of fish, as well as insects and other invertebrates. Some predators include European perch (Perca fluviatilis), cranefly (Chaoborus obscuripes), and the common roach (Rutilus rutilus) (Elenbaas 2013).
Vinegar is an important pollutant to study because it can be linked to pertinent issues in our ecosystems today, such as ocean acidification (Riebesell & Tortell, 2011). It is already known that vinegar lowers the heart rate with in vivo rats (Sugiyama, et al., 2003), and acidic environments in general lead to behavioral changes in Atlantic cod (Stiasny, et al., 2016), but we want to find out what the impacts are on smaller aquatic creatures, like Daphnia magna.
Due to the fact that acidity in aquatic environments led to health problems in cod (Stiasny, et al., 2016), and vinegar caused a decrease in heart rate with in vivo rats (Sugiyama, et al., 2003), we hypothesize that the heart rate of D. magna will decrease as the concentration of vinegar increases. To investigate this question, we obtained a living D. magna specimen and put it under the microscope. We then administered water as a control, and counted the heart rate of the test subject in beats per minute, and then we repeated that process for increasing concentrations of vinegar (0.00%, 0.01%, 0.1%, 1%, 5%, and 10%).
Methods
To conduct this experiment, we obtained a living Daphnia magna and placed it on a clear slide on the stage of the microscope on the 4x magnification setting (40x total magnification). Because D. magna is a transparent organism, we turned the rheostat on the microscope to the highest setting to let as much light into the lens as possible, and we adjusted the iris diaphragm to give us contrast. The heart of D. magna can be easily identified using Figure 1. We used the D. magna in the water as a control group and observed the heart rate for fifteen seconds, and we multiplied that value by four to calculate the heart rate in beats per minute. We repeated this process with 6 total water droplets by removing each drop with a Kimwipe and adding another. A Kimwipe is a wipe that allows us to remove excess water from the slide, but if the specimen touches the Kimwipe, it will die. In order to allow the D. magna to adjust to the changing environment, we waited one minute after we added a new water drop to the slide. After the observations in the water were complete, we put the D. magna in the recovery tank provided, and we obtained a new D. magna.
With the new test subject, we followed this same process with different concentrations of vinegar. We started with 0.00%, then 0.01%, 0.1%, 1%, 5%, and 10%, and we waited two minutes after each change in concentration. After the treatments were delivered, we again returned our D. magna to the recovery tank. With the results we obtained from four trials of both the control group and the treatment group, we took the means and standard deviations to create a graph. On the graph we included error bars that correspond to the standard deviation of each point plotted. We used these error bars to determine the significance of our results.
Results
Our data indicated that the 0.00% vinegar concentration treatment resulted in the highest heart rate in Daphnia magna (beats per minute), and the 10% vinegar concentration treatment resulted in the lowest heart rate. There was a significant difference between the water treatment and the vinegar treatment in terms of D. magna heart rate at the 10% vinegar concentration level due to the space between the error bars (Fig. 2). Tables 1 and 2 outline the individual results of each trial for water and vinegar treatments.
Table 1: The effect of water on the heart rate of Daphnia magna (beats per minute)
Drop
Trial 1
Trial 2
Trial 3
Trial 4
Mean
St. Dev.
1
264
220
264
252
250
20.78
2
232
240
276
296
296
30.18
3
288
268
256
264
264
13.61
4
272
212
256
192
233
37.29
5
268
248
276
172
241
47.48
6
296
256
260
204
254
37.88
Table 2: The effect of vinegar on the heart rate of Daphnia magna (beats per minute)
Concentration
Trial 1
Trial 2
Trial 3
Trial 4
Mean
St. Dev.
0.00%
296
308
196
276
269
50.42
0.01%
284
264
204
280
258
37.02
0.1%
264
312
164
256
249
61.82
1%
252
296
196
252
249
40.97
5%
256
212
144
208
205
46.12
10%
180
28
92
116
104
62.82
Figure 2: The effect of vinegar on the heart rate of Daphnia magna
Conclusion
Our results indicate that the treatment of vinegar to the Daphnia magna caused their heart rate to decline, and they confirmed our original hypothesis. We modeled the decrease in heart rate that we observed in D. magna graphically (Fig. 2). The average beginning heart rate for the subjects was 269, and the ending heart rate after the treatment of 10% vinegar was 104, almost a 40% decrease (Table 2). Our findings could be applied to the problem of ocean acidification. This refers to what happens when the pH levels in the water get too low, and in the natural environment, it’s largely due to increasing CO2 levels (Riebesell & Tortell, 2011). Since D. magna are very susceptible to environmental changes, ocean acidification could have deadly impacts (De Meester, et al., 1999), but there are negative impacts for larger animals too, such as cod, including changes in behavior, sensory damage, and tissue damage (Stiasny, et al. 2016). The possible implications of ocean acidification could be drawn from this experiment. If the pH in bodies of water decrease to dangerous levels, it could have drastic impacts on the wildlife. A possible error in our research is that after the 5% vinegar treatment, our D. magna was killed by the Kimwipe, and we had to retrieve another test subject. This could lead to inconsistent results. Studies similar to ours have tested the impacts that other drugs and treatments including nanoparticles (Villegas-Navarro, et al., 2003; Lovern, et al., 2007), so additional studies could test the impact of vinegar or another acidic substance on larger animals. D. magna are very small creatures, and it would be interesting to investigate if larger sea animals, like fish, would react the same way to the treatment.