This experiment seeks to answer the experimental question: "to what extent does warming have an impact on the escape speed of male and female North American fiddler crabs in marshland habitats?" Prior to conducting this experiment, preliminary research based on Vianna et. al. (2020) was conducted to understand the effects of global warming on percent time spent in burrow retreat among North American fiddler crab's (Uca pugilator). Trials were conducted under which fiddler crabs were exposed to environmental temperature ranges of 24-26°C (negative control), 27-29°C (experimental arm), and 31-33°C (positive control).

The initial experimental data revealed that in positive control (31-33°C) trials, the fiddler crabs spent 26% more time in their burrows compared to negative control (24-26°C) trials. In a two-tailed correlated t-test, the percentage of time fiddler crabs spent in burrow retreat for the positive control arm (31-33°C) when compared to the negative control arm (24-26°C) showed a statistically-significant difference (p = 0.0017). A correlated t-test was used given the same subjects were evaluated under each temperature condition. Additionally, a two-tailed t-test was used instead of a one-tailed t-test given that the experiment’s design did not limit outcomes and the averages could be either greater than or less than one another. A two-tailed correlated t-test comparing the experimental arm (27-29°C) to the negative control arm (24-26°C) showed a statistically significant difference in percentage of time fiddler crabs spent in burrow retreat (p = 0.048). This data demonstrates that sustained exposure to increased environmental temperatures increases the percentage of time fiddler crabs spend in burrow retreat as hypothesized. While these findings provided new data on the percentage of time fiddler crabs spent in burrow retreat for Uca pugilator – a species that has not previously been studied –, they also supported findings from Vianna et. al's study. Vianna et. al's 2019 experiment found that percentage of time fiddler crabs spent in burrow retreat time increased by approximately 20% ranges with Leptuca uruguayensis and Leptuca leptodactyl, two species native to São Paulo, Brazil (Vianna et al., 2020, p.1). 

The data from this study further demonstrated the dependency across multiple fiddler crab species on burrowing as a thermoregulatory mechanism – essential for the survival of ectotherms (Hews et al., 2021). Based on the significant effect that increased environmental temperature had on the percentage of time fiddler crabs spent in burrow retreat, it was determined that further research should be conducted to better understand temperature's effect on other physiologic behaviors, specifically locomotion. By better understanding temperature's effects on fiddler crab locomotion, greater insight into the downstream effects of global warming on marshland ecosystems could be gained.

Fiddler crabs were evaluated under the same three temperature conditions as the preliminary research: 24-26°C (negative control), 27-29°C (experimental arm), and 31-33°C (positive control). Fiddler crab distance traveled after the first five seconds of exposure to the predator stimulus was used as a means to evaluate the crabs' immediate escape response, which is crucial for evading predators. 

As hypothesized, the data from this study demonstrated that as environmental temperature increased, the distance traveled after five seconds decreased. While the experimental temperature (27-29°C) when compared to the negative control (24-26°C) did not show a statistically significant difference in distance traveled (two-tailed correlated t-test, p = 0.382), the positive control (31-33°C) did show a statistically significant decline in distance traveled (p = 0.00272) when compared to the negative control (24-26°C). These results indicate that fiddler crabs will likely be able to adapt to slight increases in temperature over time. However, with more extreme temperature swings brought on by global warming, on the hottest days of the year, fiddler crab sprint speed will likely decrease given their inability to physiologically adapt at these higher temperatures.

Unlike the 5-second time point, both the positive control (31-33°C) and experimental arm (27-29°C) when compared to the negative control (24-26°C) showed a statistically significant decrease in displacement after two minutes (negative to positive control, p = 0.036, negative to experimental arm, p = 0.038). This data signifies that even a slight increase in temperature had significant effects on the fiddler crabs two minutes after exposure to the predator stimuli. The decrease in displacement as temperature increases over a two minute period shows that increased environmental temperatures affect both physiological and psychological escape response. The decreased displacement by fiddler crabs at higher temperatures after two minutes may suggest that there is a decrease in their sustained fear response as temperature increases. This data compared with the data from the five-second time point suggests that temperature plays a greater role in altering the predator escape behavior of fiddler crabs over a longer period. 

These above findings highlight the ways in which fiddler crabs’ survival responses may be weakened as a result of rising temperatures from climate change, which in turn will alter predator prey dynamics. Further research should again focus on evaluating more continuous and discrete temperature ranges to determine the temperature threshold at which the decline in physiologic performance is statistically significant. Additionally, future experiments should evaluate fear response using longer trial periods to better understand the effects of temperature across extended periods of time. 

Given the high standard deviation for the experimental arm and positive control (experimental +/- 31 cm, positive +/- 30 cm) and given that there was only a 1 cm difference between their average displacement, it is possible to assume a source of error could have been in the heat lamp set up. Three heat lamps were used to cover the testing area; however, due to the size of the heat lamps, certain areas were left unevenly heated, possibly leading to fiddler crabs to seek shade rather than avoiding the predator stimulus. Future replicate studies should ensure even heat is applied across the sand using larger heat lamps. 

The graphs above present the average distance and displacement of the fiddler crabs, segregated by sex, five seconds (Figure 4a) and two minutes (Figure 4b) after exposure to a predator stimulus at each of the three studied temperature conditions: 24-26°C, 27-29°C, and 31-33°C. A two-tailed correlated t-test was conducted, comparing the responses of male and female crabs at each temperature condition for each time point. There were no statistically significant differences between sex in their escape response both five seconds and two minutes after exposure to a predator stimulus. This lack of significant differences between the two sexes indicates that the data from future studies can be aggregated. This simplification is beneficial for large-scale studies where separating test subjects by sex may not be feasible. Furthermore, these findings suggest that climate change is likely to have the same impact on male and female fiddler crabs.

Overall, the experimental findings support that fiddler crab locomotion decreases as heat stress becomes too great to overcome at extreme temperatures. Statistically significant differences in fiddler crab displacement at positive control temperatures (31-33°C) were observed for both the five-second and two-minute time points. However, the same results were not seen at experimental arm temperatures (27-29°C). 

Two minutes after exposure to the predator stimuli at the experimental temperature range, fiddler crabs showed a statistically significant difference in distance traveled. While they also showed a decrease in distance traveled after five seconds, this was not statistically significant. These results do not provide conclusive evidence to support the hypothesis but rather suggest that fiddler crabs may have the ability to adapt their immediate predator response to slight temperature increases. This is a promising result because it indicates that when temperature increases, a fiddler crab's short term ability to evade predators may not be affected. However, it is important to note that a fiddler crabs' sustained fear response is affected by temperature increases. Thus, future research should be conducted to better understand the relationship between temperature and long term fear response.

Despite these unexpected results, this study provides new evidence filling a previous knowledge gap of how fiddler crab sex may impact their response to increases in environmental temperatures. Across all time point and temperature comparisons of male to female fiddler crabs, no statistically significant differences were found. This data supports the idea that sex does not affect fiddler crab's physiological response to increases in temperature. This sex-neutral response not only enables future researchers to evaluate these species as an aggregate, but it also raises questions about whether similar patterns exist for other physiological processes and across other crustacean species. If sex-based differences do exist, this could result in a shift in species populations which would have downstream effects on reproduction, altering the delicate balance within marshland ecosystems. Future studies on sex-based differences in physiologic response to heat stress should be conducted to help researchers better understand the potentially wide-spread impact of climate change on other marine ecosystems.

Based on the results from this study, the fiddler crab populations could become severely strained if locomotor function decreases due to elevated environmental temperatures. As sprint speed in the face of predators is slowed, fiddler crabs become easier prey, leading to population decline. Long-term changes in this population will make it more difficult for birds to find food during their migrations, potentially disrupting migratory patterns and migratory bird populations (Zeil et al., 2006). With fewer birds surviving migration, insects, rodents, and other prey will face fewer predatory threats and their populations will thrive. These changes in population across multiple species could severely destabilize the closely interconnected marshland ecosystems leading to eventual collapse.

 In addition to the effects that decreased fiddler crab populations pose to other animal populations, a proliferation in microalgal blooms can also be expected. According to Dai et al. (2023), algal blooms increased in frequency by 59% across 54 large marine ecosystems between 2003 and 2020 due to climate change. Fiddler crabs currently account for the consumption of up to 70% of microalgal biomass making them key to regulating algal blooms (Johnson et al., 2020). By consuming detritus, fiddler crabs manage populations of microalgae, or unicellular microorganisms that create algal biomass through photosynthesis (Ruane et al., 2010). With fewer fiddler crab populations, algal blooms could become even more frequent in the presence of global warming. These algal blooms cause mass die-offs and dead zones because photosynthetic algae absorb a significant amount of oxygen, blocking sunlight from underwater species. A recent algal bloom near Tampa, Florida, created a dead zone, killing upwards of 1,700 tons of aquatic life (University of South Florida Ocean Circulation Lab, n.d.). In addition to these population disruptions affecting the fishing industry, people can also be exposed to these toxins via the fish that they consume (Rolton et al., 2022, p. 1).

To examine this, further a theoretical study examining two factors could address how sex and temperature affect fiddler crabs’ consumption of algae. This study could provide valuable insights into algal bloom prevalence and ecological changes in the presence of climate change. Overall, fiddler crabs are key organisms to keeping balance in marshland and are crucial to understanding how marshlands might be affected as climate change takes hold.