title: Reproductive Toxicology of Sea Turtles
Creators: name: Barraza, Arthur D
Publisher: name: Griffith University
Year: 2023
Subjects: subject: ecotoxicology
subject: sea turtles
subject: contaminants
subject: reproduction

description: Many sea turtle species are threatened or endangered because of human activities including habitat loss, bycatch, and pollution. Various studies from around the world have found that anthropogenic contaminants accumulate within sea turtle tissues. Sea turtles have high site fidelity to coastal habitats, which are often close to human development, and therefore, pollutant sources. However, limited research has been performed on the impacts of contaminants on sea turtle reproduction. These research gaps were addressed by conducting a quantitative literature review of reptile reproductive toxicology to inform sea turtle reproductive toxicology research (Chapter 2). Three research priorities for better understanding reproductive toxicology in sea turtles were identified. These included: assessing contaminant exposure and maternal transfer in nesting sea turtles of known foraging locations (Chapter 3), investigating impairment of sex hormone production and the prevalence of common endocrine disruptors in sea turtles at various foraging locations (Chapter 4), and exploring the potential for contaminants to influence the sex determination of sea turtle hatchlings (Chapter 5). A chemical risk assessment of two loggerhead sea turtle (Caretta caretta) nesting beaches in eastern Australia revealed a direct link between nesting turtle foraging location and hatchling contaminant concentrations (Chapter 3). There were significant differences in contaminant exposure and maternal transfer between two nesting locations, and these differences were directly correlated with known turtle foraging locations. Particularly, nesting turtle foraging locations reflected many of the contaminant differences found. There were also correlations between maternal blood and egg contaminant concentrations for a number of trace elements. In addition, cytotoxicity in a sea turtle specific cell-based bioassay suggested that organic contaminant concentrations in the blood of turtles foraging in some locations may be high enough to cause cell damage in vitro. Overall, however, the risk of trace elements and organic contaminant exposure to hatchling health were considered low at both nesting beaches. Despite this, these data suggest that reducing contaminant exposure in foraging locations could translate to reductions in trace element concentrations in hatchling turtles. Within the five green turtle foraging grounds investigated in Chapter 4, there was evidence of widespread exposure to ethinylestradiol (EE2) and nonylphenol (NP) in immature green turtles. EE2 and NP are known endocrine disruptors, and well-studied for their negative estrogenic effects on aquatic organisms. EE2 and NP have been found to alter sex determination and alter sex hormone production in reptiles including freshwater turtles. EE2 residues in immature green turtles were up to 10 times higher than persons taking EE2 medication. There is little research as to whether EE2 and NP can maternally transfer to offspring. Maternal transfer of these compounds may lead to feminization of offspring. This study demonstrated that EE2 and NP exposure was common across many foraging locations in Queensland, and that the effects of these compounds on reproductive endpoints need to be investigated further. In Chapter 5, sixteen green turtle clutches that were part of a parallel study on the impacts of nest cooling on sex ratios were examined for their trace element and organic contaminant concentrations. The contaminants found were converted into three indices: the percent of hatchlings in a clutch with trace element concentrations over median (TEOM), the percent of hatchlings in a clutch with estrogenic trace element concentrations over median (EstroEOM), and a predicted 17β-estradiol equivalent activity (PEEQA) of estrogenic trace elements. Many of the clutches deviated from their predicted sex ratio based on temperature (hereby sex ratio deviation), with some clutches having 90% more females than expected. When excluding an outlier, sex ratio deviation had a significant positive relationship with cadmium, antimony, and EstroEOM. In addition, there were significant relationships between mean clutch concentrations of cobalt, lead, antimony, barium, PEEQA, TEOM, EstroEOM and sex ratio. While there were no specific contaminants found to definitively affect sex determination, overall contaminant trends suggested that contaminants may affect sea turtle hatchling sex determination. This thesis contributes to the priorities of sea turtle reproductive toxicology research that were established in the literature review (Chapter 2). Overall, I found that that sea turtle foraging grounds can influence hatchling contaminant accumulation in nesting populations; immature turtles are exposed to endocrine disrupting compounds within their foraging grounds; and that the potential effects of contaminants on sea turtle hatchling sex determination should be the subject of future studies. These research outcomes support management and conservation of sea turtles, illustrating that reducing contaminant inputs at sea turtle foraging locations can help reduce the potential reproductive harm of anthropogenic activities, and therefore may reduce the risk hatchling feminization from contaminants.