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

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.

Climate change and temperature‐linked hatchling mortality at a globally important sea turtle nesting site

“…We recorded similar seasonal patterns of sand temperature across the six years of measurements (Figure ), which suggest that temperature‐related hatchling survival and sex ratio are also likely to be similar. This lack of inter‐annual variability is similar to that recorded at other rookeries such as Ascension Island (Hays, Godley, & Broderick, ) where rainfall is minimal during nesting season, but contrasts to the patterns recorded on the east coast of the United States (e.g., Hawkes, Broderick, Godfrey, & Godley, ; Lolavar & Wyneken, ) where rainfall is more important. So at Cape Verde we expect that, over short time periods, the key drivers of variations in hatchling sex ratio production might be seasonal effects (more males at the start and end of the season) and across‐beach effects rather than cooling produced by rainfall or tidal overwash, which may be important at other sites across the world (e.g., Godfrey, Barreto, & Mrosovsky, ; Houghton et al., ; Lolavar & Wyneken, ; Laloë, Esteban, Berkel, & Hays, ).…”

Climate change increases the production of female hatchlings at a northern sea turtle rookery

“…Several studies have highlighted the importance of considering temperature variations during the thermosensitive period for sexual differentiation (Georges 1989, Georges et al 1994), and fluctuations have been shown to be substantial in freshwater turtles, which lay shallow nests (Georges 1989). However, a combination of thermal buffering and deeper egg chambers in sea turtle nests tend to lessen the effects of temperature fluctuations (DeGregorio and Williard 2011, Lolavar and Wyneken 2015). Moreover, multiple laboratory and field studies have since validated the use of incubation duration as an appropriate estimation for hatchling sex ratios, and have been conducted on loggerhead populations nesting in the United States, Brazil, Greece and Cyprus (Godfrey and Mrosovsky 1997, Mrosovsky et al 1999, Godley et al 2001, Fuller et al 2013.…”

How will changes in local climate affect hawksbill hatchling production in Brazil?

“…Consequently, projections show a lower decrease in hatching success under the more extreme climate change scenario, RCP8.5, as it projects higher increases in precipitation when compared to the conservative scenario (RCP4.5). Wetter, more moist conditions may offset increases in temperature maintaining cooler sand temperatures [15, 46-48]. However, as climate change progresses and conditions become wetter, there is a potential for further reductions in hatchling production, since very wet conditions can result in soil saturation or a rise of the water table level displacing air between sand particles, suffocating embryos and resulting in clutch failure [28, 49, 50].…”