Sand temperatures for nesting sea turtles in the Caribbean: Implications for hatchling sex ratios in the face of climate change
Introduction
It is widely reported that climate change is having a profound impact on the functioning of ecosystems (Hoegh-Guldberg and Bruno, 2010). Species abundances and distributions are shifting due to the changing environment (Jones and Cheung, 2015, Poloczanska et al., 2013). The breeding phenology of migratory species is also changing in response to environmental change (e.g. McCarty, 2001, Parmesan et al., 1999, Walther, 2010). Furthermore, climate change-induced habitat loss puts species at risk of extinction when no alternative adequate habitat is available (Foden et al., 2013). The risk of climate change is particularly pronounced for marine ectotherms as they conform more closely to thermal tolerance limits than terrestrial ecotherms (Sunday et al., 2012) and, in particular, species whose biology and phenology are intimately linked to temperature (Somero, 2010). Of particular concern are species that exhibit-temperature-dependent sex determination. This applies to the majority of reptiles, including sea turtles. The concern of climate change is of particular importance to sea turtles considering that six out of the seven species are classified as critically endangered, endangered or vulnerable by the International Union for the Conservation of Nature (IUCN, 2014).
One of the conservation challenges for sea turtle ecologists is that climate change is impacting sea turtles in more than just one way. For instance, sea level rise may cause a loss of the beaches on which the females rely to nest (Fish et al., 2008, Fuentes et al., 2009a). Climate change models also predict an increase of rainfall and storm events at certain sites, which may be detrimental to nests as exposure to high levels of water negatively impacts the success of a nest (Patino-Martinez et al., 2014). Increasing air temperatures is also a concern for species that exhibit temperature-dependent sex determination and may lead to skewed sex ratios and local extinctions (Janzen, 1994). As such, increasing temperature was recently identified as one of the biggest threats to sea turtle populations' viabilities (Fuentes and Cinner, 2010).
Quantifying how warming temperatures will impact sea turtle populations across the globe is a conservation priority. A recent thread of research concerns the reconstruction of past sex ratios at important breeding sites based on historical air temperature data (e.g. Hays et al., 1999, Hays et al., 2003). These studies are important in informing how primary sex ratios fluctuated in the past. By using climate projections provided by the Intergovernmental Panel on Climate Change (IPCC) it is also possible to make projections on how the primary sex ratios may change in the future. This is of particular interest when trying to assess if a population is at risk of extinction in the near future due to climate change.
Current models used to estimate primary sex ratios are primarily based on air temperatures records alone (e.g. Hawkes et al., 2007, Hays et al., 1999, Hays et al., 2003). Such models are proven to be robust but having more variables may improve the model and make the reconstructions more accurate (Fuentes et al., 2009b). Working with the best available model is important when trying to accurately assess how global warming will affect the viability of sea turtle populations across the globe. The current study examines an array of environmental variables that may influence sand temperature of Zeelandia beach, St. Eustatius. Two hundred year time-series of incubation temperatures and primary sex ratios for the three species of turtles nesting at this site were then constructed. The results of this study inform on the extinction risks of these populations of sea turtles and help establish whether conservation efforts, such as shading or relocating nests, would be beneficial at this site.
Section snippets
Study site
The island of St. Eustatius (17.5°N, 63.0°W) is located in the Lesser Antilles in the North-eastern Caribbean (Fig. 1), with a land area of 21 km2. Green (Chelonia mydas), hawksbill (Eretmochelys imbricata) and leatherback (Dermochelys coriacea) turtles nest on St. Eustatius. The present study was conducted on Zeelandia beach (encompassing Turtle Beach to the South), a 1.6 km beach on the eastern, windward, exposed coastline of St. Eustatius where a monitoring programme of nesting turtles has
Sand temperature and environmental variables
Five loggers were lost due to beach erosion or hurricanes. Loggers lost mid-season were replaced with new loggers. Data from the 15 loggers that were successfully retrieved were downloaded using Tinytag Explorer 4.7 and checked to ensure that logger time was synchronised with local time at the field site (GMT-4 h). Datasets were reviewed and data before logger deployment and after logger retrieval were removed. When processing the data monthly means were used. We excluded months for which days
Discussion
Mean sand temperatures recorded at the study site were relatively high (29.1–33.3 °C) compared to other nesting beaches around the World. For example, mean sand temperatures at nest depths during nesting season were 29.0–31.0 °C in North Carolina, USA (De Gregorio and Southwood Williard, 2011), 29.5 and 32.2 °C for light and dark-coloured beaches respectively at Ascension Island (central Atlantic) (Godley et al., 2002); 30.3–32.4 °C in Barbados (Caribbean) (Horrocks and Scott, 1991); 29.5–33.2 °C in
Author contributions
NE and GCH conceived the study, NE led the fieldwork with assistance from JB, J-OL led the data analysis with contributions from all authors, all authors contributed to the writing. J-OL and NE are joint first authors.
Acknowledgements
The authors thank Dr. Erik Meesters and Selma Ubels, IMARES, Netherlands for providing additional albedo values collected during a separate MSc study. IMARES funded fieldwork for NE in 2012. The authors acknowledge use of the Maptool program (www.seaturtle.org, last accessed on 29 May 2015) for production of Fig. 1. The study was conducted within the Statia National Marine Park programme and complied with all relevant local and national legislation. Numerous STENAPA staff and volunteers, in
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2022, Science of the Total EnvironmentCitation Excerpt :This raises concerns with regard to global warming, sea level rise and increased storminess (Patrício et al., 2021). Some turtle rookeries around the world are demonstrating the effects of increasing global temperatures through skewed sex ratios towards females, which threatens populations (Chatting et al., 2021; Laloë et al., 2016; de Marcovaldi et al., 2016). Green turtles (Chelonia mydas) from warmer nesting beaches on the northern Great Barrier Reef, showed extremely biased sex ratios, with 99.1% of juvenile, 99.8% of subadult, and 86.8% of adult-sized turtles being female (Jensen et al., 2018).
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2021, Ocean and Coastal ManagementCitation Excerpt :Eggs incubated at ~29 °C produce a 50:50 sex ratio, called the pivotal temperature (PT), and temperatures above the PT produce predominantly females and vice versa (Mrosovsky, 1994). For all seven species of marine turtles, there is a thermal range of 25–33 °C in which egg incubation is successful (Howard et al., 2014; Spotila and Standora, 1985), and temperatures towards the higher threshold (prolonged exposure above 33 °C) can result in morphological abnormalities and increased hatchling mortality (Hawkes et al., 2007; Hays et al., 2003; Laloë et al., 2016; Packard et al., 1977). Rising temperatures due to anthropogenic climate change could have negative impacts on all life stages of sea turtles.