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

Abstract

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.

Biology and conservation of marine turtles in the northwestern Indian Ocean: a review

“…Hindcasting of sex ratios (1993−2018) gave approximately 73% female hatchling production and increasing to > 95% from 2075 to 2100 (Chatting et al 2021). Tanabe et al (2020) calculated the expected sex ratio of both green and hawksbill turtles in the Red Sea and showed that sites could already be exceeding thermal maximums and may be vulnerable to rising temperatures. On the contrary, findings from Pilcher at al.…”

Satellite Tracking of Post-nesting Green Sea Turtles (Chelonia mydas) From Ras Baridi, Red Sea

“…In 1989 the National Center for Wildlife (NCW) [formerly the National Commission for Wildlife Conservation and Development] initiated detailed studies of multiple aspects of the nesting turtles, including their morphology and their nesting success (Al-Merghani et al, 2000;Pilcher and Al-Merghani, 2000;Al-Mansi et al, 2003;Al-Mansi, 2016). In addition to studies concerning the turtles, physical characteristics of the beach and environmental factors were studied to determine their impact on the hatching success of eggs (Al-Mansi et al, 1991;Pilcher, 1999;Tanabe et al, 2020). Jensen et al (2019) defined a unique genetic allele from the green turtles nesting at Ras Baridi.…”

Newly described nesting sites of the green sea turtle (Chelonia mydas) and the hawksbill sea turtle (Eretmochelys imbricata) in the central Red Sea

“…Our findings highlight the shortage of information on sea turtle nesting throughout most of the Saudi Arabian Red Sea. This is not an unexpected result: Ras Baridi is the only well-studied nesting area in the region ( Miller, 1997 ; Pilcher, 1999 ; Pilcher & Al-Merghani, 2000 ; Tanabe et al, 2020 ; Shimada et al, 2021a ; Shimada et al, 2021b ; Al-Mansi et al, 2021 ). Expanding research efforts at other sites should be a priority in the face of rapid coastal development.…”

“…Dust from the nearby cement factory was also present, but in very small quantities, indicating that recent mitigation efforts to reduce beach contamination have been largely successful ( MEPA, 1983 ). We hypothesise that sediment composition at Ras Baridi could be responsible for the increased sand temperature at this site compared to other Red Sea nesting sites ( Tanabe et al, 2020 ) from increased sand albedo.…”