Trace elements in green turtle eggshells and coral sand sediments from the Xisha Islands, South China Sea

Metal accumulation in female green sea turtles (Chelonia mydas) from Eastern Atlantic affects their egg quality with potential implications for embryonic development

Sea turtles, with their global distribution and complex life cycle, often accumulate pollutants such as metals and metalloids due to their extended lifespan and feeding habits. However, there are limited studies exploring the impact of metal pollution on the reproductive health of female sea turtles, specifically focusing on the quality of their eggs, which has significant implications for the future generations of these charismatic animals. São Tomé Island, a crucial nesting and feeding habitat for green sea turtles, underscores the urgent need for comprehensive research in this ecologically significant area. This study aimed to investigate whether metals and metalloids in the blood of nesting female green sea turtles induce genotoxic effects in their erythrocytes and affect their egg morphometric characteristics and the composition of related compartments. Additionally, this study aimed to evaluate whether the quality of energetic reserves for embryo development (fatty acids in yolk's polar and neutral lipids) is influenced by the contamination status of their predecessors. Results revealed correlations between Cu and Hg levels and increased "lobed" erythrocytes, while As and Cu negatively influenced shell thickness. In terms of energy reserves, both polar and neutral lipid fractions contained primarily saturated and monounsaturated fatty acids, with prevalent 18:1n-9, 18:0, 16:0, 14:0, and 12:0 fatty acids in yolk samples. The yolk polar fraction was more susceptible to contaminant levels in female sea turtles, showing consistent negative correlations between pollution load index and essential n3 fatty acids, including linolenic, eicosatrienoic, eicosapentaenoic, and docosapentaenoic acids, crucial for embryonic development. These metals accumulation, coupled with the reduced availability of these key fatty acids, may disrupt the eicosanoid and other important pathways, affecting reproductive development. This study reveals a negative correlation between metal contamination in female sea turtles' blood and egg lipid reserves, raising concerns about embryonic development and the species' future generations.

Microplastic Distribution Characteristics and Sources on Beaches That Serve as the Largest Nesting Ground for Green Turtles in China

The threat of microplastics to marine animals and habitats is increasing, which may affect sea turtle nesting grounds. The Qilianyu Islands are the largest remaining green turtle (Chelonia mydas) nesting grounds in China. Despite being far from the mainland, microplastic pollution cannot be ignored. In this study, the level of microplastic pollution in surface sediments from three different zones, namely, the bottom, intertidal, and supratidal zone, was investigated on North Island, Qilianyu Islands. The results showed that the abundance of microplastics in the supratidal zone was significantly higher than that in the bottom zone and intertidal zone (r = 3.65, p = 0.011), with the highest average abundance of microplastics located on the southwest coast of North Island. In the bottom zone, only plastic blocks (88%) and fibers (12%) were found. The main types of microplastics in the intertidal and supratidal zones were plastic blocks (48%) and foam (42%), with polyethylene (PE) (40%) and polystyrene (PS) (34%) being the predominant components. These types and components of microplastics differed from those in the surrounding seawater, but corresponding types and components were found in the plastic debris on the beach. Meanwhile, it was also observed that there were multiple instances of fragmented plastic on the beach. Thus, we suggest that the microplastics on the beach in North Island were mainly derived from the fragmentation of microplastic debris, indicating secondary microplastics. It is recommended to further strengthen the regular cleaning of plastic debris on the beach, especially the removal of small plastic debris, in order to reduce the pollution from secondary microplastics generated by the fragmentation of beach plastic debris and to better protect China's most important sea turtle nesting site in the South China Sea.

Revisiting the genetic diversity and population structure of the endangered Green Sea Turtle (Chelonia mydas) breeding populations in the Xisha (Paracel) Islands, South China Sea

The Green Sea Turtle (Chelonia mydas) is an umbrella species in the South China Sea, a Chinese national first-level protected wild animal, and the only sea turtle that nests in waters around China. The largest C. mydas nesting ground is distributed in the Xisha (Paracel) Islands, which plays a vital role in the survival of sea turtle populations in the region. This study reveals the genetic diversity and population structure of the breeding population of C. mydas in the Xisha (Paracel) Islands using three mitochondrial markers. A total of 15 D-loop, five Cytochrome b (Cyt b), and seven Cytochrome C Oxidase subunit I (COI) haplotypes were identified in the breeding population of C. mydas in the Xisha (Paracel) Islands. D-loop haplotypes are distributed in clades III, IV, and VIII of the C. mydas mitochondrial control region. It is the first time that one haplotype from Clade IV was found in this C. mydas population, and five new D-loop haplotypes were also identified. The haplotype and nucleotide diversity were calculated for each marker: D-loop (0.415 haplotype diversity, 0.00204 nucleotide diversity), Cyt b (0.140, 0.00038) and COI (0.308, 0.00083). The average genetic distance (p) of each molecular marker was less than 0.01. Neutral detection and nucleotide mismatch analysis suggested that the breeding population of C. mydas in the Xisha (Paracel) Islands did not experience a population expansion event in recent history. It is recommended that a sea turtle protection area be established in the Xisha (Paracel) Islands area to strengthen protection and effectively protect the uniqueness and sustainability of the breeding population of C. mydas in the South China Sea.

Assessment of trace element contamination in the historical nesting grounds of green sea turtle (Chelonia mydas) in Hainan Island, China

Trace element pollution is a potential threat to the reproduction of sea turtles. Hainan Island was previously the most important nesting ground of green sea turtles in China before they disappeared approximately 36 years ago. The Chinese government has encouraged restoration work on historical nesting grounds, and it is necessary to evaluate the status of these sites before conducting habitat restoration. This study analyzed the concentrations of seven trace elements in the surface sediments of 13 historical nesting grounds in Hainan. The average concentrations were 19.47 (Cr), 4.67 (Ni), 6.99 (Cu), 0.08 (Cd), 16.68 (Pb), 0.02 (Hg), and 5.27 (As) mg/kg, which were lower than the first-grade limit values of the GB (18668-2002) national standard in China. The concentrations were close to the background value, except for the relatively high Cd value. The potential ecological risk was ranked as Cd > Hg > As > Cu > Pb > Cr. The spatial distribution of trace element contamination in Hainan was uneven, with high potential ecological risk levels of Cd and Hg contamination in Longwan'gang, Shimeiwan, Yazhou Qu, and Fushicun. Marine mariculture, wastewater discharge, and fishing boats are the main sources of trace element contamination in Hainan. We recommend strengthening the control of Hg and Cd contamination sources, monitoring trace elements in relevant/interest areas, and the environmental protection department should curb local residents from directly discharging mariculture wastewater and domestic sewage into the sea.

Transfer and accumulation of trace elements in seawater, sediments, green turtle forage, and eggshells in the Xisha Islands, South China Sea

Chemical pollutants present a substantial threat to the survival of the green turtle (Chelonia mydas). In this study, the concentrations of 12 trace elements (TEs) in seawater, sediments, and green turtle forage and eggshells from the Xisha Islands in the South China Sea, along with their patterns of transfer and accumulation, were identified. The results revealed that the median TE concentrations in seawater and sediments were lower than the first-grade limit values of the national standard in China, indicating a low ecological risk. The concentrations (μg·g-1) of TEs in forage ranged from 0.05-0.69, 3.43-14.4, 157-2391, 27.9-124, 2.05-9.39, 0.30-9.78, 2.01-80.50, 0.18-5.76, 0.06-0.98, 2.00-18.4, 0.02-0.24, and 0.01-0.09 for Cr, Mn, Sr, Fe, Ni, Cu, Zn, Se, Cd, As, Pb, and Hg, respectively. Seawater, sediments, turtle forage, and eggshells exhibited different TE profiles, which were driven by Hg, Sr, Cr, and Pb in seawater and sediments; Fe and Ni in sediments; Cd and As in forage; and Zn, Se, and Cu in eggshells. The contents of Cu, Zn, and Se increased slightly with trophic level, indicating that they were transferred through dietary pathways. Although Cd and As appeared to bioaccumulate in green turtle forage, it was not transferred to their eggshells, which may be related to the excretion and metabolism process in the mother's body. Thus, eggshells may be a poor bioindicator for the exposure of female green turtles to these toxic elements.

Microplastic pollution at Qilianyu, the largest green sea turtle nesting grounds in the northern South China Sea

Microplastics, new persistent pollutants, have recently attracted considerable attention. When present in beach sediments, microplastics may adversely affect the nesting and hatching of sea turtles on beaches. In this study, we investigate microplastic pollution at Qilianyu (northeastern Xisha Islands), the largest known nesting ground for green sea turtles (Chelonia mydas) in China. We found that the average abundance of microplastics in the beach surface sediments was 338.44 ± 315.69 thousand pieces·m^-3 or 1,353.78 ± 853.68 pieces·m^-2, with foam and fragments as the main microplastic type identified. The microplastic particles were categorised as small and were predominantly within the 0.05-1 mm size category. Most microplastic particles were white (71.31%). Polystyrene and polyethylene were found to be the most common forms of plastic present. Microplastic pollution was not only observed on the beach surface but also at the bottom of nests approximately 60 cm may be harmful to the incubation of sea turtle eggs. We suggest removing plastic litter, especially small pieces of plastic, on beaches to reduce the threat of microplastic pollution to marine life, including sea turtles. Furthermore, the foam used in aquaculture should be recovered and replaced before it becomes fragmented due to age. In addition, regional cooperation between stakeholders in the South China Sea should be strengthened to collectively promote the reduction and cleanup of marine litter.