Testing & Results
Introduction
The hypothesis tested during this longitudinal study of the Uca minax fiddler crab species at Spermaceti Cove on Sandy Hook, New Jersey is as follows: The Uca minax fiddler crab species located at Spermaceti Cove on Sandy Hook, New Jersey will increase as the years go on. The null hypothesis for this study is as follows: There will be no difference in the Uca minax population at Spermaceti Cove on Sandy Hook, New Jersey over the years. The hypothesis was tested using the same method that was used in previous years in order to mitigate error and increase the accuracy of the study.
This longitudinal study is important, as fiddler crabs are an indicator species; there is a direct correlation between their population stability and the health of their habitat. Should their habitat be unhealthy or receiving increasing amounts of pollutants, the amount of fiddler crabs seen will decrease. Conversely, if the salt marsh these fiddler crabs live in is thriving, their population will also thrive. By conducting this experiment, it determines the population of the Uca minax fiddler crab species at Spermaceti Cove on Sandy Hook, New Jersey.
Method: How the Hypothesis Is Tested
This longitudinal study began in June 2016 and studies the changes in population of the Uca minax fiddler crabs on Spermaceti Cove at Sandy Hook, New Jersey.
Materials for this experiment include Microsoft Excel to organize data and conduct statistical analysis and a blog on Blogger.com. Tide charts were procured from nj.usharbors.com. All data is in a binder for organizational purposes. Electronic versions of the data are in Excel spreadsheets.
The data was collected at low tide during full and new moons from June 2016 to October 2017. The crabs are most active during low tide. New and full moons and low tides ensured fiddler crabs were out of their burrows for counting. Fiddler crabs were counted once every two weeks. Counting took place at Spermaceti Cove on Sandy Hook, New Jersey during the Uca minax fiddler crab breeding season, from June to October. After October, counting sessions ended.
Spermaceti Cove was divided into northern and southern parts, with the wooden walkway being the divider between each site. This allows facilitated counting, as one person counted the north side, while another person counted the south side.
Qualitative data recorded during each count included the following: wind speed and direction in miles per hour, air temperature in Celsius, the presence of litter, and weather conditions. Observation of fiddler crab predators' tracks, such as humans, marine birds, and raccoons, were recorded, as predators could have eaten the fiddler crabs, decreasing the count.
All observations and counting sessions were recorded in a Microsoft Excel spreadsheet.
Line and bar graphs were produced using the data. Several statistical analyses of the data were completed. A correlation between the temperature of the counting day and the amount of fiddler crabs counted on both sides of Spermaceti Cove for the 2017-2018 data collection year was conducted. Mean, standard deviation, and variation were calculated for the 2016-2017 and 2017-2018 data sets. A t-test of the counts in June, July, and August of both data sets were conducted.
Statistical Analysis
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Figure 1: The above graph shows the amount of Uca minax fiddler crabs counted on both the North and South sides of Spermaceti Cove on Sandy Hook, New Jersey during the 2016-2017 data collection set. This is the baseline data for this longitudinal study.
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Figure 2: The above graph shows the amount of Uca minax fiddler crabs counted on both the North and South sides of Spermaceti Cove on Sandy Hook, New Jersey during the 2017-2018 data collection set.
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A correlation between the temperature of the counting day in Celsius and the amount of Uca minax fiddler crabs counted on both sides of Spermaceti Cove concluded that they have a slightly positive correlation of .31056. Evidentially, on a warmer day, more fiddler crabs will be spotted, as past counting sessions have shown (see Figure 3 for the numbers needed to make this calculation and Figure 4 for a table of the date of the counting session, air temperature in Celsius of the day, and amount of fiddler crabs counted).
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Figure 3: Above is a table of all of the numbers necessary to calculate the correlation between temperature and amount of crabs counted.
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Figure 4: Above is a table of the date the crabs were counted, with the amount of crabs counted and the temperature in Celsius. It is shown that a higher temperature also yields a higher amount of fiddler crabs counted the majority of the time.
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Mean, standard deviation, and variance of the 2016-2017 baseline data set and the 2017-2018 data set were calculated in order to determine the spread of the data. (see Figure 5).
On the other hand, the difference in variance between the south side of the cove between both data sets is significantly less, with a variance of 48,062.8 in the 2016-2017 data set and 47,435.1. This means that the amount of crabs spotted on the south side were relatively close to each other each counting session. The same is true of the standard deviation between both sides of Spermaceti Cove, with a bigger difference of standard deviation on the north side than on the south side in both data sets.
The amount of fiddler crabs counted in the summer months, June, July, and August, of 2016 and 2017 were statistically compared using a t-test to determine the differences between the summers of both years. Using a t-distribution table, the t-test number with an alpha level of .05 and 5 degrees of freedom should have been 2.015, not the 1.943 that was calculated. This means that the null hypothesis cannot be disproven.
Summary and Conclusion
By using the same method for this experiment as conducted in previous years, the population status of the Uca minaxpopulation can be attained. Statistical analysis of the amount of fiddler crabs counted at Spermaceti Cove during the crab's breeding season tested the hypothesis.
The results of this longitudinal study were not as predicted. The t-test provided evidence that the null hypothesis of this experiment cannot be disproven. This voids the hypothesis stating that the fiddler crab population at Spermaceti Cove would increase as the years go on. The population of Uca minax fiddler crabs at Spermaceti Cove on Sandy Hook, New Jersey shows no significant change over the years. The data collected in this study and the statistical analysis conducted on it backs this statement.
Further work is necessary to determine exactly why there is no significant change in population as years progress. One possible explanation is that the population of Uca minax fiddler crabs at Spermaceti Cove has already reached its carrying capacity, and no more fiddler crabs can thrive in the habitat due to the amount of resources, such as food and water, in it.
Longitudinal studies become more accurate as more years of data is collected. With more counting sessions each year, there will be more data points to statistically compare, making the conclusions more reputable. As the study continues, the conclusions conducted will become more accurate, as more years will be statically compared to each other.
Although the method for collecting data for this study remains the same from year to year, each year different people work on the study. This means that there could be slight variations in the way that data is collected, whether it be the counters being more negligible and careless when counting the crabs or not accurately recording descriptive data, like wind speed and direction and air temperature.
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