The Effect of Temperature on Loggerhead Sea Turtles, Caretta caretta, with Emphasis on Nesting in Broward County, Florida

Defense Date

9-22-2005

Document Type

Capstone

Degree Name

M.S. Marine Biology

Second Degree Name

M.S. Coastal Zone Management

First Advisor

Curtis Burney

Second Advisor

Edward Keith

Abstract

Temperature plays a significant role in the life histories of sea turtles. The loggerhead sea turtle, Caretta caretta, uses temperature cues for growth, reproduction, nesting, migration, etc. Although the majority of a sea turtle’s life is spent in the water, the females and hatchlings also utilize the terrestrial environment. Therefore both water temperatures and sand temperatures influence sea turtles. Water temperatures dictate migration, nesting, growth, internesting intervals, and mating. Sand temperatures are equally important because they aid in nest site selection, determine incubation time, and hatchling sex ratio. Global warming may have a significant impact on sea turtles because of their dependence on temperature. While some other species have already been observed to be changing in conjunction with climate warming, sea turtle activities have not yet been documented to be significantly responding to global temperature change. It is possible that small changes have been occurring over time but they have not been significant enough to be currently detected. Changes in temperature will affect loggerhead sea turtles primarily with regard to reproduction. With temperature dependent sex ratios, loggerhead populations are in danger of skewed hatchling populations if sand temperature changes drastically. Other effects may occur such as a decrease in the availability of food or an increase in predators. If the ecosystem does not also change in response to the temperature increases, other resources, such as food availability, may become limiting especially if nesting is altered and changes the timing of hatching, mating, etc. In one study by Weishampel et al. (2004) it was suggested that loggerhead turtles on the east central coast of Florida were nesting earlier due to an increase in sea surface temperatures. The median Julian date of nesting in this area was significantly earlier by 10 days between the years 1989 to 2003. A similar study was conducted with loggerhead sea turtle nesting in Broward County, Florida. The Julian dates of the first nest, the first 90% of nests, and the last nest declined significantly between 1994 and 2004. There were nearly significant declines in the Julian dates of the first 1%, 10%, and 50% of the nests during this time. This indicates that the nesting season may be shifting slightly earlier in more recent years compared to the earlier years between 1994 and 2004. However as with the Weishampel study, sea surface temperatures were not determined to be increasing in a statistically significant trend. Therefore although sea surface temperatures can not be significantly correlated to this earlier nesting trend, it is possible that some other factor or combination of factors is contributing to earlier nesting. Because temperature determines a number of functions for sea turtle life histories it is possible that these changes in nesting times are still a result of some temperature differences. With global temperature changes imminent continued research and conservation will be imperative to a continued understanding of sea turtle behavior and to their survival.

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