Major aggregations of nesting green turtles (Chelonia mydas) occur in the northern Red Sea, although little is known about the reproductive ecology of this endangered species in the region. To address this issue, we satellite-tracked 30 female green turtles to document their movements and to identify factors driving habitat use at two major rookeries in the Red Sea, Jazirat Mashabah (Mashabah Island) and Ras Al Baridi in Saudi Arabia. Between successive nesting events, turtles displayed high fidelity to nesting beaches and adjacent in-water habitats (inter-nesting habitats). Using generalized linear mixed models, we estimated the mean probability of nesting per beach emergence (nesting success rate) to be 0.628, and the mean duration between a successful nesting event and the successive emergence onto the beach (re-nesting interval) to be 10.8 days at each site. The nesting success rate was relatively high (>0.8) when the preceding daytime land surface temperature (LST) was lower than 37°C but decreased with elevated daytime LST (<0.4 when >47°C). Re-nesting interval was longer at lower water temperatures and towards the end of the nesting season of individuals. Our study improves the robustness of abundance estimates from census data (e.g., track counts) and shows that the protection of nesting and inter-nesting habitats during a breeding season would be an effective conservation strategy for the species. We discuss how global warming could increase energy expenditure due to lowered nesting success, ultimately compromising the reproductive fitness of these populations.

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Coral reefs across the tropics have already been heavily degraded by climate change and are expected to become increasingly imperiled as the oceans continue to warm (Hoegh-Guldberg et al., 2014). However, many coral reefs are located in oceanographically complex coastal zones, where temperatures are modulated by a variety of physical processes (

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Climate 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.