Honors College Thesis

Too Hot to Handle: Impacts of increasing temperatures on early life history stages of Tiger Grouper (Mycteroperca tigris) from Little Cayman, Cayman Islands

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  • The early life history stages of fish are typically the most sensitive to environmental change, particularly regarding temperature. With tropical ocean temperatures projected to increase over the next fifty years, documenting how the development of larval fishes changes under different temperature regimes is crucial to understand how these changes will affect population dynamics. Tiger Grouper (Mycteroperca tigris) is an economically and ecologically important reef fish distributed throughout the Caribbean that aggregates to spawn during colder winter months. We collected embryos from spawning events on the west end of Little Cayman, Cayman Islands, using established techniques from the Grouper Moon Project, and reared embryos and larvae at 25°C and 27°C (within current temperature variability) and 29°C and 31°C (within predicted elevated temperatures in the next 100 years) for up to three days. Embryos and larvae were photographed, and measurements of various morphometrics were taken (i.e., standard length, total length, oil globule diameter, yolk sac diameter, body depth, etc.) at 1 -, 2-, and 3- days post fertilization (dpf). Rates of embryo ascension for Tiger Grouper embryo groups at different hours post fertilization (hpf) were measured. Due to the allocation of embryos into treatment groups resulting in uneven sample sizes, this study draws from qualitative data of the photogrammetry process with some support from statistical analysis. Kruskal Wallis and Dunn’s tests were performed for each growth measurement along with the embryo ascension rates; for the body measurements, only samples from 2 dpf were statistically analyzed. There were few statistically significant p-values returned from the Kruskal-Wallis test, with the only statistically significant difference being between MDV measurements (p < 0.05) (Figure 5, E); however qualitative analysis of the temperature treatments and subsets suggests negative impacts of increased temperature on their development. The qualitative analysis suggests faster absorption of yolk sacs and oil globules occurred at higher rates in the elevated temperature groups of 29°C and 31°C, possibly due to increase metabolic rates from the increased temperature, which would direct energy away from growth and towards combating the effects of temperature. Recommendations for future research repeating similar studies on Tiger Grouper with a larger sample size and comparing their anatomical development and ascension rates with closely related species. In addition to this, the reevaluation of the Tiger Grouper conservation status would be of high priority, as this can best inform how future management of this species changes in addition to the impacts of climate change on the area.
  • Keywords: Climate change, Biology, Tiger Grouper, Fish Early Life History
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