Nest temperatures and rainfall for the 2010 to 2013 loggerhead turtle nesting seasons at Boca Raton, Florida [2010 and 2011 shown]. Incubation temperatures measured in each nest are shown by the gray plot lines. The red shading indicates the published transitional range of temperatures (TRT) over which males and females may occur in Florida (Girondot 1999). The vertical gray boxes denote the predicted thermosensitive period (TSP) for each nest during which embryonic sex is determined. Graphic: Lolavar and Wyneken, 2015 / Endangered Species Research

By Eric Niiler
17 October 2015

(Discovery News) – Sea turtles are the ocean’s “canaries in the coal mine” when it comes to climate change, according to researchers who are trying to find out how they are adapting to a warmer climate that may be leaving baby male turtles high and dry.

Recent studies have shown that warmer temperatures in sea turtle nests -- which lie buried under several feet of beach sand -- produce more female turtles. Since turtles have been around for more than 100 million years, biologists still don’t know why a slight shift in temperature can mean more females than males.

They also don’t know whether this “feminization” of turtle eggs will spell the end of sea turtle reproduction over the long term, or is just the turtle’s way of adapting to natural cycles of warmer and cooler weather that happen each year.

A new study of nesting loggerhead turtles in South Florida has found that rainfall helps cool off the hot sand, but in recent years the females have been hatching more females because of hotter, drier weather.

“If climatic changes continue to force the sex ratio bias of loggerheads to even greater extremes, we are going to lose the diversity of sea turtles as well as their overall ability to reproduce effectively,” said Jeanette Wyneken, a marine biologist at Florida Atlantic University. “That’s why it’s critical to understand how environmental factors, specifically temperature and rainfall, influence hatchling sex ratios.”

The four-year study examined the loggerhead nesting season, which runs from April through October, and buried instruments in the sand at three depths to measure both temperature and moisture.

“The majority of hatchlings in the sampling were female, suggesting that across the four seasons most nest temperatures were not sufficiently cool to produce males,” said Wyneken. “However, in the early portion of the nesting and in wet years, nest temperatures were cooler, and significantly more males hatched.”

Wyneken and her team published their study in the journal Endangered Species Research this month. [more]

Warmer Beaches Mean Fewer Florida Sea Turtles

ABSTRACT: Marine turtles deposit their eggs in underground nests where they develop unattended and without parental care. Incubation temperature varies with environmental conditions, including rainfall, sun/shade and sand type, and affects developmental rates, hatch and emergence success, and embryonic sex. We documented (1) rainfall and sand temperature relationships and (2) rainfall, nest temperatures and hatchling sex ratios at a loggerhead turtle (Caretta caretta) nesting beach in Boca Raton, Florida, USA, across the 2010 to 2013 nesting seasons. Rainfall data collected concurrently with sand temperatures at different depths showed that light rainfall affected surface sand; effects of the heaviest rainfall events tended to lower sand temperatures but the temperature fluctuations were small once upper nest depths were reached. This is important in understanding the potential impacts of rainfall as a modifier of nest temperatures, as such changes can be quite small. Nest temperature profiles were synchronized with rainfall data from weather services to identify relationships with hatchling sex ratios. The sex of each turtle was verified laparoscopically to provide empirical measures of sex ratio for the nest and nesting beach. The majority of hatchlings in the samples were female, suggesting that across the 4 seasons most nest temperatures were not sufficiently cool to produce males. However, in the early portion of the nesting season and in wet years, nest temperatures were cooler, and significantly more males hatched.

Effect of rainfall on loggerhead turtle nest temperatures, sand temperatures and hatchling sex



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