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Journal of Experimental Marine Biology and Ecology

Effect of predicted sea level rise scenarios on green turtle (Chelonia mydas) nesting

Abstract

There is a growing interest among scientists about climate change and its adverse effects. One of the major adverse effects of climate change is the sea level rise (SLR), which will cause habitat loss for many species and threaten their survival. Sea turtles are an example of animal groups most likely to be threatened by SLR. It is, therefore, critical to predict the effect of SLR on sea turtle habitats to prepare better conservation and management plans that consider the climate change impact. With this aim, we projected the outcomes of SLR on the habitat and nest loss of one of the most important Mediterranean green sea turtle ( Chelonia mydas ) nesting beaches (Samandag, Turkey) using natural nests between 2008 and 2016 nesting seasons. Under the extreme scenario (1.2 m SLR) one-third of the coastal area and up to 18% of natural nests could be lost at a key green turtle nesting beach for this globally unique population.

Introduction

There is growing evidence that climate change is adversely affecting nest building animals directly (Mainwaring et al., 2017). Suboptimal temperatures, for example, negatively influence the sex of the offsprings of species with temperature dependent sex determination (TSD) like sea turtles (Hawkes et al., 2007; Laloë et al., 2014), meaning there are female biased hatchling sex ratios or increased embryonic mortality (Hawkes et al., 2007; Reneker and Kamel, 2016; Tanner et al., 2019). Furthermore, climate driven sea level rise (SLR) (Fuentes et al., 2010) could adversely affect habitats of threatened, endangered, and endemic species such as sea turtles in coastal areas (Fish et al., 2005; Hawkes et al., 2009; Varela et al., 2019). Current projections by the Intergovernmental Panel on Climate Change (IPCC) suggest that under realistic scenarios the global SLR will be 0.47 m to 0.63 m by 2100 (Collins et al., 2013). However, SLR may be higher than expected based on quasi-experimental models over the same period (De Conto and Pollard, 2016; Vousdoukas et al., 2018).

Nesting beaches are critical habitat for sea turtles because successful reproduction depends on access to sandy beaches with favorable conditions for embryonic development within buried nests (Ackerman, 1997). It is, therefore, important to understand how SLR will influence the sea turtle nesting beaches. In a study on green turtle (Chelonia mydas) populations of the Great Barrier Reef, Australia, flooding of nests as a direct result of SLR was the greatest threat to reproduction (Fuentes et al., 2010). Furthermore, an experimental study with flooding of green turtle nests showed that submergence in saltwater for 1 or 3 h reduced the viability of the eggs by less than 10% (Pike et al., 2015). Under different global SLR scenarios (ranging between 0.18 m and 1.3 m), the loss rate in nesting habitats of different sea turtle species was between 24% and 89% (Fish et al., 2005, Fish et al., 2008; Mazaris et al., 2009; Fuentes et al., 2010; Katselidis et al., 2014; Hiebert et al., 2017). Such a reduction in available nesting area could cause density related problems for successful embryonic development (Limpus et al., 2003; Fish et al., 2008; Fuentes et al., 2010). However, sea turtles may exhibit adaptive responses to ongoing climate change effects such as altering their nesting phenology (earlier nesting), nest site selection (nesting in cooler areas), or nest design (digging deeper nests) (Hays et al., 2002; Mazaris et al., 2009; Weishampel et al., 2010; Mainwaring et al., 2017). Therefore, predicting potential effects of SLR on sea turtle nesting habitats before they occur is important for understanding possible conservation interventions to reduce the negative effects of SLR. This is a key point for achieving effective conservation measures since ignoring potential climate change impacts in conservation plans will probably be unsuccessful (Rilov et al., 2020).

Research on effects of climate change, particularly SLR, on sea turtles in the Mediterranean is limited to a few studies (Mazaris et al., 2009; Katselidis et al., 2014; Varela et al., 2019). The main nesting beaches of the Mediterranean green turtle regional management unit (Wallace et al., 2010) are constrained to the eastern Mediterranean (Casale et al., 2018) with the main nesting sites occurring in Turkey, Cyprus, and Syria (Casale et al., 2018). Samandag Beach, Turkey, is one of the most important green turtle nesting grounds in the Mediterranean (Türkozan and Kaska, 2010; Casale et al., 2018) with a mean of 241 nests annually (Yalçın Özdilek and Sönmez, 2011). Samandag Beach is regularly exposed to floods due to the deterioration of the beach slope, which put nests close to the tide line under risk for flooding and erosion. (Kasparek et al., 2001; Yalçın Özdilek, 2007; Sönmez and Yalçın-Özdilek, 2013). Previous studies suggested that relocation of nests at high risk of flooding was a worthwhile conservation activity (Yalçın Özdilek, 2007; Sönmez and Yalçın-Özdilek, 2013). We focused this study on Samandag Beach because the adverse effects of SLR on this beach will likely be reflected across the Mediterranean green turtle population's nesting range. Our aims in this study were (ı) to predict habitat loss; (ıı) to estimate nest loss based on natural nest locations; and (ııı) to create effective conservation measures that account for potential effects of climate change.

Section snippets

Study site and nesting data

Data were collected on Samandag Beach, Turkey (36"07′N, 35″55′E) during the 2008–2016 nesting seasons (between early May to late September). The beach is approximately 14 km in length, extending from the Çevlik Harbour in the north to Sabca Promontory in the south, and is divided into three sub-sections: (1) Çevlik (5.5 km); (2) Şeyh-Hızır, (4 km); and (3) Meydan sub-section, (4.5 km) (Yalçın Özdilek, 2007). The Çevlik sub-section extends between the Çevlik Harbour and the Şeyh-Hızır Tomb and

Results

We recorded 3479 green turtle nests during nine breeding seasons (between 2008 and 2016), with a mean of 387 nests annually. The total beach area was 1,140,690 m2 and the mean beach elevation was 1.42 m. The total beach area and elevation for each sub-sections are presented in Table 1. The largest beach area was in Şeyh-Hızır with having 39.6% of the total beach area. The sub-sections of the beach differ in terms of mean elevation (Kruskal–Wallis: chi-squared = 2922.78, df = 2, P = 0.001) with

Discussion

Under the 0.48 m, 0.63 m and 1.2 m SLR scenarios, 9.7%, 13.1%, and 31.8% of the total available nesting area on Samandag Beach would be lost, respectively. The densest nesting sub-section, Şeyh-Hızır, would be the least affected, while Çevlik would be the most affected. Almost half of the total nesting area (45%) on the Çevlik will be lost under the most extreme SLR scenario (1.2 m) due to lower mean beach elevation (mean 0.8 m) compared to the other sub-sections. Concordantly, previous studies

Conclusions

In conclusion, the habitat loss and, as a result, nest destruction due to inundation or density dependent factors are inevitable during SLR because of climate change. The overall Samandag beach may lose one-third of the coastal habitat under the worst scenario (1.2 m). The core ideas identified by KDE may be used as a potential nest relocation points in case of inundation in the future. However, sea turtles may give adaptive responses to decrease the effect of SLR and increase the survival

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author statement

Corresponding author (BS) collected field data. All authors worked together to create orthophoto photographs, elevation data and determine core areas. In addition, in the writing of MS, all three authors acted together and wrote simultaneously.

Declaration of Competing Interest

We declare no conflicts of interest.

Acknowledgements

Nesting data were collected within the framework of a protocol on sea turtle research and conservation between the Hatay Nature Conservation and National Parks of the Ministry of Agriculture and Forestry and the Samandag District Governorship (2008–2011), and the Association for Samandag Environmental Protection and Tourism (2012–2016). We would like to thank Samandag Municipality and map technician Hüseyin Gün for supplying the coastal elevation data. We also would like to thank Prof. Dr.

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