Potential feminization of Red Sea turtle hatchlings as indicated by in situ sand temperature profiles

Lyndsey K Tanabe,Joanne Ellis,Islam Elsadek,Michael L Berumen

doi:10.1111/csp2.266

Abstract

AbstractClimate change poses a serious threat to species that demonstrate temperature‐dependent sex determination, including marine turtles. Increased temperatures can result in highly female‐skewed sex ratios and decreased hatching success. The pivotal temperature that delineates hatchling sex ratios is commonly considered to be 29.2°C, but whether this threshold applies to turtles in the Red Sea region has not been tested in situ. For all species of marine turtles, there is a supposed thermal range of 25–33°C in which egg incubation is successful, with prolonged temperatures above 33°C resulting in morphological abnormalities and hatchling mortality. Sand temperature data were collected from May–September 2018 from the average nesting depth of hawksbill (Eretmochelys imbricata) and green turtles (Chelonia mydas) at five study sites. We calculated the expected sex ratio based on a maximum likelihood model. The sand temperature profile at four of the sites exceeded the pivotal temperature (29.2°C) throughout the study duration, which suggests feminization of turtles could be occurring; however, the pivotal temperature in this region still needs to be empirically confirmed. The percentage of days with sand temperature exceeding the maximum thermal threshold between June 3, and September 16, 2018, was site‐specific rather than determined by latitudinal temperature gradients, and ranged between 0 and 100% of days. Maximum temperature recordings were as high as 36.0 and 35.3°C at 30 and 50 cm depth, respectively. Nesting sites in the Red Sea region could already be exceeding the thermal limits and may be particularly vulnerable to rising temperatures. Sites with lower sand temperatures, such as Small Gobal Island, may represent priority areas for conservation efforts. Alternatively, local adaptation may be a reality under extremely warm conditions, thus, further research into the thermal tolerance of hatchlings in the region could provide insight on how they might adapt to future climate change.

Highlights

There are seven extant species of marine turtles, which share common life-history traits that make them vulnerable to environmental change and anthropogenic impacts
Despite survival through past climatic shifts, current rates of change are likely unprecedented for tens of millions of years (Zeebe, Ridgwell, & Zachos, 2016), leading to a rising concern of how present-day populations will respond to anthropogenic climate change, as they face other humaninduced threats (Root, Price, Hall, & Schneider, 2003)
Marine turtles demonstrate temperature-dependent sex determination, which is a common trait of some vertebrates including turtles, crocodiles, and some fish species (Valenzuela & Lance, 2004)

Summary

Introduction

There are seven extant species of marine turtles, which share common life-history traits that make them vulnerable to environmental change and anthropogenic impacts. These characteristics include a long lifespan, late sexual maturity, cyclic migrations between nesting and feeding grounds, fidelity to foraging habitats, and dependence on low-lying sandy beaches to lay their clutches. Marine turtles first appeared during the late Triassic period 220 million years ago (Li, Wu, Rieppel, Wang, & Zhao, 2008) and have since survived and adapted to climate changes throughout their evolutionary history (Harris, 1993). Marine turtles demonstrate temperature-dependent sex determination, which is a common trait of some vertebrates including turtles, crocodiles, and some fish species (Valenzuela & Lance, 2004). There are significant implications to these species in the face of climate change (Hawkes, Broderick, Godfrey, & Godley, 2009)

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