In-nest mortality and pathology of hawksbill sea turtle (Eretmochelys imbricata) embryos and hatchlings in St. Kitts and Nevis

Strategies to improve the hatch success and survival of critically endangered hawksbill turtles (Eretmochelys imbricata) require knowledge of threats to them including pathological conditions. The objective of this study was to describe the mortality and pathology of embryos and dead-in-nest hatchlings on St. Kitts and Nevis. Over the 2019/20 and 2020/21 nesting seasons, the combined mean (SD) hatch success for the two islands was 81.9% (13.2%) and deceased individuals within excavated nests were early-stage embryos (70.7%), late-stage embryos (17.7%), pipped-hatchlings (8.2%) or dead-in-nest hatchlings (3.4%). From 2017 to 2021, a post-mortem examination was performed on 183 turtles, including histology for 116. Anatomical malformations affected 77 (42.1%) examined turtles and included abnormal scute shape or number (22.4%), dysmelia (8.7%), schistosomus reflexus (7.7%) and compressed carapace (7.7%). Microscopic lesions were found in 49.1% of turtles and included tissue mineralization (26.7%, including renal, fetal membrane, liver, heart or muscle), chorioallantoitis (16.2%) and skeletal muscle degeneration and necrosis (10%). Inflammatory lesions associated with fungal or bacterial infections were in the skin (n = 3), chorioallantois (n = 4), lung (n = 3) or yolk sac (n = 1). These lesions may reflect non-specific terminal conditions but their presence in-nest helps explain some of the mortality and pathology documented in hatchlings that die during rehabilitative care. All of the gonads adequately represented for histological determination of sex were female (n = 62), supporting concern for feminization of Caribbean hawksbill turtle nests. The study identifies lesions that could affect hatch and emergence success. The high frequency of skeletal malformations indicates the need for investigations addressing regional impact and pathogenesis, especially genetic and environmental aetiologies including nest temperature. Immediate examination of live hatchlings on nest emergence is warranted to better determine the prevalence of non-fatal malformations that could impact fitness and population genetics.

Short-term resilience to climate-induced temperature increases for equatorial sea turtle populations

Projection models are being increasingly used to manage threatened taxa by estimating their responses to climate change. Sea turtles are particularly susceptible to climate change as they have temperature-dependent sex determination and increased sand temperatures on nesting beaches could result in the 'feminisation' of hatchling sex ratios for some populations. This study modelled likely long-term trends in sand temperatures and hatchling sex ratios at an equatorial nesting site for endangered green turtles (Chelonia mydas) and critically endangered hawksbill turtles (Eretmochelys imbricata). A total of 1078 days of sand temperature data were collected from 28 logger deployments at nest depth between 2018 and 2022 in Papua New Guinea (PNG). Long-term trends in sand temperature were generated from a model using air temperature as an environmental proxy. The influence of rainfall and seasonal variation on sand temperature was also investigated. Between 1960 and 2019, we estimated that sand temperature increased by ~0.6°C and the average hatchling sex ratio was relatively balanced (46.2% female, SD = 10.7). No trends were observed in historical rainfall anomalies and projections indicated no further changes to rainfall until 2100. Therefore, the sex ratio models were unlikely to be influenced by changing rainfall patterns. A relatively balanced sex ratio such as this is starkly different to the extremely female-skewed hatchling sex ratio (>99% female) reported for another Coral Sea nesting site, Raine Island (~850 km West). This PNG nesting site is likely rare in the global context, as it is less threatened by climate-induced feminisation. Although there is no current need for 'cooling' interventions, the mean projected sex ratios for 2020-2100 were estimated 76%-87% female, so future interventions may be required to increase male production. Our use of long-term sand temperature and rainfall trends has advanced our understanding of climate change impacts on sea turtles.

Contribution of plastic and microplastic to global climate change and their conjoining impacts on the environment - A review

Plastics are fossil fuel-derived products. The emissions of greenhouse gases (GHG) during different processes involved in the lifecycle of plastic-related products are a significant threat to the environment as it contributes to global temperature rise. By 2050, a high volume of plastic production will be responsible for up to 13 % of our planet's total carbon budget. The global emissions of GHG and their persistence in the environment have depleted Earth's residual carbon resources and have generated an alarming feedback loop. Each year at least 8 million tonnes of discarded plastics are entering our oceans, creating concerns regarding plastic toxicity on marine biota as they end up in the food chain and ultimately affect human health. The unsuccessful management of plastic waste and its presence on the riverbanks, coastlines, and landscapes leads to the emission of a higher percentage of GHG in the atmosphere. The persistence of microplastics is also a significant threat to the fragile and extreme ecosystem containing diverse life forms with low genetic variation, making them vulnerable to climatic change. In this review, we have categorically discussed the contribution of plastic and plastic waste to global climate change covering the current plastic production and future trends, the types of plastics and plastic materials used globally, plastic lifecycle and GHG emission, and how microplastics become a major threat to ocean carbon sequestration and marine health. The conjoining impact of plastic pollution and climate change on the environment and human health has also been discussed in detail. In the end, we have also discussed some strategies to reduce the climate impact of plastics.

The ecological impact of plastic pollution in a changing climate

Assessing three interlinked issues, plastic pollution, climate change and biodiversity loss separately can overlook potential interactions that may lead to positive or negative impacts on global ecosystem processes. Recent studies suggest that threatened species and ecosystems are vulnerable to both plastic pollution and climate change stressors. Here we consider the connectivity and state of knowledge between these three environmental issues with a focus on the Global South. Nine out of top ten Long-Term Climate Risk Index (CRI) (2000-2019) ranked countries are located within the Global South, yet research is focused in the Global North. A literature search for the top ten Long-Term Climate Risk Index (CRI) (2000-2019) ranked countries matched a total of 2416 (3.3% of global publications) search results on climate change, with 56 (4% of the global publications) on plastic pollution, and seven (7.7% of the global publications) on both climate change and plastic pollution. There is a strong correlation between the Global South and high biodiversity hotspots, high food insecurity and low environmental performance. Using Bangladesh as a case study, we show the erosion rates and sea level rise scenarios that will increase ocean-bound plastic pollution and impact high biodiversity areas. Poverty alleviation and promoting renewable energy and green practices can significantly reduce the stress on the environment. We recommend that these connected planetary threats can be best addressed through a holistic and collaborative approach to research, a focus on the Global South, and an ambitious policy agenda.

Detection and assessment of marine litter in an uninhabited island, Arabian Gulf: A case study with conventional and machine learning approaches

In 2018, the Ministry of Municipality and Environment, Qatar removed 90 t of marine litter (ML) from the Ras Rakan Island (RRI), a remote uninhabited island in the Arabian Gulf (hereinafter referred to as Gulf). To identify the sources of ML and understand the post-cleaning ML accumulation rate, a ML survey was conducted around RRI in 2019. A total of 1341 ML items were found around RRI with an average abundance of 3.4 items/m². In addition, a machine learning approach was applied to extract the quantity and types of ML from 10,400 images from the sampling sites (beaches) to make the ML clean-up process and monitoring effort more efficient. The image coordinates of ML objects were used to train an object detection algorithm 'You Only Look Once (YOLO-v5)' to automatically detect ML from video data. An image enhancement technique was performed to improve the quality of unclear images. The best performing YOLO-v5 model had 90% of mean Average Precision (mAP) while maintaining near real-time processing speeds at 2 ms/image. The abundance of ML around RRI was higher than that found on the coast of mainland Qatar. 61.5% of the sampling locations are considered as 'extremely dirty' based on Clean Coast Index. Windward beaches had higher ML concentrations (derived from neighbouring countries) than the leeward beaches. Like RRI, most of the uninhabited islands in the Arabian Gulf are home to many seabirds and sea turtles, and could act as major sinks for ML deposition. Therefore, implementation of this machine learning technique to all islands allows estimating and mitigating the load of ML for achieving a sustaining and a cleaner ocean.

The fundamental links between climate change and marine plastic pollution

Plastic pollution and climate change have commonly been treated as two separate issues and sometimes are even seen as competing. Here we present an alternative view that these two issues are fundamentally linked. Primarily, we explore how plastic contributes to greenhouse gas (GHG) emissions from the beginning to the end of its life cycle. Secondly, we show that more extreme weather and floods associated with climate change, will exacerbate the spread of plastic in the natural environment. Finally, both issues occur throughout the marine environment, and we show that ecosystems and species can be particularly vulnerable to both, such as coral reefs that face disease spread through plastic pollution and climate-driven increased global bleaching events. A Web of Science search showed climate change and plastic pollution studies in the ocean are often siloed, with only 0.4% of the articles examining both stressors simultaneously. We also identified a lack of regional and industry-specific life cycle analysis data for comparisons in relative GHG contributions by materials and products. Overall, we suggest that rather than debate over the relative importance of climate change or marine plastic pollution, a more productive course would be to determine the linking factors between the two and identify solutions to combat both crises.

Reconstructing past thermal conditions in beach microclimates

Reconstruction of past conditions provides important information on how ecosystems have been impacted by climate change, but generally for microhabitats worldwide there are no long-term empirical measurements. In these cases, there has been protracted debate about how various large-scale environmental proxies can best be used to reconstruct local temperatures. Here we help resolve this debate by examining how well environmental proxies hindcast sand temperatures at nest depths for five sea turtle nesting sites across the world. We link instrumental air temperature and sea surface temperature records with empirical sand temperature observations in the Atlantic (Ascension Island and Cape Verde), the Indian Ocean (Chagos Archipelago), the Caribbean (St Eustatius) and the Pacific (French Polynesia). We found strong correlations between sea surface temperatures, air temperatures and sand temperatures at all our study sites. Furthermore, Granger causality testing shows variations in sea surface temperature and air temperature precede variations in sand temperatures. We found that different proxies (air or sea temperature or a combination of both) predicted mean monthly sand temperatures within <0.5°C of empirical observations. Reconstructions of sand temperatures over the last 170 years reveal a slight warming of temperatures (maximum 0.5°C per century). An analysis of 36 published datasets revealed that the gradient of the relationship between sand temperature and air temperature is relatively constant, suggesting long-term changes in sand temperature could be extended around the world to include nesting sites where there are no empirical measurements of sand temperature. Our approaches are likely to have utility for a range of microhabitats where there is an interest in long-term changes in temperature.