Health status and genetic compositions of green turtles (Chelonia mydas) foraging in Brunei Bay

Long-term monitoring of sea turtle aggregations is critical for understanding the impacts of environmental changes on their population health and habitat suitability. Brunei Bay is a significant foraging ground for green turtles in the South China Sea. We analyzed the body size, hematology and body condition of green turtles for their health status in their foraging ground in Brunei Bay over a period of nine years (2011-2019). Additionally, we used mitochondrial DNA (mtDNA) to evaluate changes in the size and genetic composition of green turtle aggregations. Our findings revealed that the size composition of the green turtle population varied seasonally, but there were no significant temporal changes in genetic and size compositions. Hematology parameters and Fulton's body condition index were consistent with those reported for apparently healthy green turtles. Furthermore, we found that blood reference intervals indicated the turtles were healthy. These results provide valuable baseline data for future comparisons with other foraging aggregations and for long-term monitoring of green turtles in Brunei Bay.

18S rDNA amplicon sequence data (V1–V3) of the Palmyra Atoll National Wildlife Refuge, Central Pacific

To address the global biodiversity crisis, standardized data that are rapidly obtainable through minimally invasive means are needed for documenting change and informing conservation within threatened and diverse systems, such as coral reefs. In this data paper, we describe 18S rRNA gene amplicon data (V1–V3 region) generated from samples collected to begin characterizing coral reef eukaryotic community composition at the Palmyra Atoll National Wildlife Refuge in the Central Pacific Ocean. Sixteen samples were obtained across four sample types: sediments from two sieved fractions (100–500 μm, n = 3; 500 μm-2 mm, n = 3) and sessile material scrapings (n = 3) from Autonomous Reef Monitoring Structures (ARMS) sampled in 2015, as well as seawater from 2012 (n = 7). After filtering and contaminant removal, 3,861 Amplicon Sequence Variants (ASVs) were produced from 1,062,238 reads. The rarefaction curves demonstrated adequate sampling depth, and communities grouped by sample type. The dominant orders across samples were polychaete worms (Eunicida), demosponges (Poecilosclerida), and bryozoans (Cheilostomatida). The ten most common orders in terms of relative abundance comprised ~60% of all sequences and 23% of ASVs, and included reef-building crustose coralline algae (CCA; Corallinophycidae) and stony corals (Scleractinia), two taxa associated with healthy reefs. Highlighting the need for further study, ~21% of the ASVs were identified as uncultured, incertae sedis, or not assigned to phylum or order. This data paper presents the first 18S rDNA survey at Palmyra Atoll and serves as a baseline for biodiversity assessment, monitoring, and conservation of this remote and pristine ecosystem.

Rehabilitation of Marine Turtles and Welfare Improvement by Application of Environmental Enrichment Strategies

Simple Summary

Sea turtles are vital members of the marine ecosystem since they contribute to keeping balance in such environments. Unfortunately, they are endangered species whose absence may be detrimental. Conservation efforts aim to preserve sea turtles both at the population and individual levels. Rescue and rehabilitation aim to reduce individual morbidity and mortality as a result of injuries mainly caused by interactions with humans, in order to preserve their genetic diversity and help maintain and/or increase their population size. Environmental enrichment (EE) is a set of methodologies aimed to improve animal welfare during captivity/rehabilitation. This review presents successful cases of sea turtle environmental enrichment and its applications to improve their welfare in captivity and to increase their fitness prior to release into the wild. EE is a valuable tool that enhances welfare during the captivity and/or rehabilitation of sea turtles and improves their chances of survival and reintegration back into wild populations upon release. EE may be adopted in rescue and rehabilitation facilities around the world to improve individual survival and help boost conservation efforts.

Abstract

Sea turtles perform various ecological services in several marine environments and are considered architects of the marine landscape. At present, they are endangered species due to anthropogenic threats, pollution and degradation of marine habitats. These impacts make it urgent to increase protection and conservation efforts. Protective actions include the rescue and rehabilitation of injured individuals as a result of their interactions with humans and other threats. Environmental enrichment (EE) is a series of techniques and methods aimed to improve the welfare of animals in captivity and/or under rehabilitation. It uses external stimuli to enhance their psychological and physiological wellbeing to promote natural abilities and behaviors. These may increase the survival chances of rehabilitated animals upon release in the wild. This review presents data of studies where EE has been applied during the rehabilitation processes of different species of sea turtles, and its effect on welfare improvement during captivity/rehabilitation and on survival after release into nature. Technologies such as satellite tags are an important means to determine rehabilitation success and survival of injured individuals from endangered species after release into the wild, as they allow tracking and monitoring of such individuals, and determine their location in areas used by their natural populations for feeding or breeding.

Sea Turtles in the Cancer Risk Landscape: A Global Meta-Analysis of Fibropapillomatosis Prevalence and Associated Risk Factors

Several cancer risk factors (exposure to ultraviolet-B, pollution, toxins and pathogens) have been identified for wildlife, to form a “cancer risk landscape.” However, information remains limited on how the spatiotemporal variability of these factors impacts the prevalence of cancer in wildlife. Here, we evaluated the cancer risk landscape at 49 foraging sites of the globally distributed green turtle (Chelonia mydas), a species affected by fibropapillomatosis, by integrating data from a global meta-analysis of 31 publications (1994–2019). Evaluated risk factors included ultraviolet light exposure, eutrophication, toxic phytoplanktonic blooms, sea surface temperature, and the presence of mechanical vectors (parasites and symbiotic species). Prevalence was highest in areas where nutrient concentrations facilitated the emergence of toxic phytoplankton blooms. In contrast, ultraviolet light exposure and the presence of parasitic and/or symbiotic species did not appear to impact disease prevalence. Our results indicate that, to counter outbreaks of fibropapillomatosis, management actions that reduce eutrophication in foraging areas should be implemented.

Sea turtles across the North Pacific are exposed to perfluoroalkyl substances

Perfluorinated alkyl substances (PFASs) are global, persistent, and toxic contaminants. We assessed PFAS concentrations in green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles from the North Pacific. Fifteen compounds were quantified via liquid chromatography tandem mass spectrometry from 62 green turtle and 6 hawksbill plasma samples from Hawai'i, Palmyra Atoll, and the Northern Marianas Islands. Plasma from 14 green turtles severely afflicted with fibropapillomatosis, and eggs from 12 Hawaiian hawksbill nests from 7 females were analyzed. Perfluorooctane sulfonate (PFOS) predominated in green turtle plasma; perfluorononanoic acid (PFNA) predominated in hawksbill tissues. Concentrations were greater in hawksbill than green turtle plasma (p < 0.05), related to trophic differences. Green turtle plasma PFOS concentrations were related to human populations from highest to lowest: Hawai'i, Marianas, Palmyra. Influence on fibropapillomatosis was not evident. PFASs were maternally transferred to hawksbill eggs, with decreasing concentrations with distance from airports and with clutch order from one female. A risk assessment of PFOS showed concern for immunosuppression in Kailua green turtles and alarming concern for hawksbill developmental toxicity. Perfluoroundecanoic (PFUnA) and perfluorotridecanoic (PFTriA) acid levels were correlated with reduced emergence success (p < 0.05). Studies to further examine PFAS effects on sea turtle development would be beneficial.

Characterizing coral reef biodiversity: genetic species delimitation in brachyuran crabs of Palmyra Atoll, Central Pacific

Coral reefs are highly threatened ecosystems, yet there are numerous challenges in conducting inventories of their vanishing biodiversity, partly because many taxa remain difficult to detect and describe. Genetic species delimitation methods provide a standardized means for taxonomic classification including of cryptic, rare, or elusive groups, but results can vary by analytical method and genetic marker. In this study, a combination of morphological and genetic identification methods was used to estimate species richness and identify taxonomic units in true crabs (Infraorder Brachyura; n = 200) from coral reefs of Palmyra Atoll, Central Pacific. Genetic identification was based on matches between mitochondrial 16S ribosomal RNA (16S rRNA) and/or cytochrome c oxidase subunit I (COI) sequences to GenBank data, while morphological work relied on the taxonomic literature. Broad agreement in the number of candidate species delimited by genetic distance thresholds and tree-based approaches was found, although the multi-rate Poisson tree process (mPTP) was less appropriate for this dataset. The COI sequence data identified 30-32 provisional species and the 16S data revealed 34-35. The occurrence of 10 families, 20 genera, and 19 species of brachyurans at Palmyra was corroborated by at least two methods. Diversity levels within Chlorodiella laevissima indicated possible undescribed or cryptic species in currently lumped taxa. These results illustrate the efficacy of DNA sequences in identifying organisms and detecting cryptic variation, and underscore the importance of using appropriate genetic markers and multiple species delimitation analyses, with applications for future species descriptions.

Potential impacts of historical disturbance on green turtle health in the unique & protected marine ecosystem of Palmyra Atoll (Central Pacific)

Palmyra Atoll, in the Central Pacific, is a unique marine ecosystem because of its remarkably intact food web and limited anthropogenic stressors. However during World War II the atoll was structurally reconfigured into a military installation and questions remain whether this may have impacted the health of the atoll's ecosystems and species. To address the issue we assessed green sea turtle (n=157) health and exposure to contaminants at this foraging ground from 2008 to 2012. Physical exams were performed and blood was sampled for testosterone analysis, plasma biochemistry analysis, hematology and heavy metal exposure. Hematological and plasma chemistries were consistent with concentrations reported for healthy green turtles. Heavy metal screenings revealed low concentrations of most metals, except for high concentrations of iron and aluminum. Body condition indices showed that <1% of turtles had poor body condition. In this study, we provide the first published blood values for a markedly healthy sea turtle population at a remote Central Pacific Atoll.

Fast growing, healthy and resident green turtles (Chelonia mydas) at two neritic sites in the central and northern coast of Peru: implications for conservation

In order to enhance protection and conservation strategies for endangered green turtles (Chelonia mydas), the identification of neritic habitats where this species aggregates is mandatory. Herein, we present new information about the population parameters and residence time of two neritic aggregations from 2010 to 2013; one in an upwelling dominated site (Paracas ∼14°S) and the other in an ecotone zone from upwelling to warm equatorial conditions (El Ñuro ∼4°S) in the Southeast Pacific. We predicted proportionally more adult individuals would occur in the ecotone site; whereas in the site dominated by an upwelling juvenile individuals would predominate. At El Ñuro, the population was composed by (15.3%) of juveniles, (74.9%) sub-adults, and (9.8%) adults, with an adult sex ratio of 1.16 males per female. Times of residence in the area ranged between a minimum of 121 and a maximum of 1015 days (mean 331.1 days). At Paracas the population was composed by (72%) of juveniles and (28%) sub-adults, no adults were recorded, thus supporting the development habitat hypothesis stating that throughout the neritic distribution there are sites exclusively occupied by juveniles. Residence time ranged between a minimum of 65 days and a maximum of 680 days (mean 236.1). High growth rates and body condition index values were estimated suggesting healthy individuals at both study sites. The population traits recorded at both sites suggested that conditions found in Peruvian neritic waters may contribute to the recovery of South Pacific green turtles. However, both aggregations are still at jeopardy due to pollution, bycatch and illegal catch and thus require immediate enforcing of conservation measurements.

Predicting connectivity of green turtles at Palmyra Atoll, central Pacific: a focus on mtDNA and dispersal modelling

Population connectivity and spatial distribution are fundamentally related to ecology, evolution and behaviour. Here, we combined powerful genetic analysis with simulations of particle dispersal in a high-resolution ocean circulation model to investigate the distribution of green turtles foraging at the remote Palmyra Atoll National Wildlife Refuge, central Pacific. We analysed mitochondrial sequences from turtles (n = 349) collected there over 5 years (2008-2012). Genetic analysis assigned natal origins almost exclusively (approx. 97%) to the West Central and South Central Pacific combined Regional Management Units. Further, our modelling results indicated that turtles could potentially drift from rookeries to Palmyra Atoll via surface currents along a near-Equatorial swathe traversing the Pacific. Comparing findings from genetics and modelling highlighted the complex impacts of ocean currents and behaviour on natal origins. Although the Palmyra feeding ground was highly differentiated genetically from others in the Indo-Pacific, there was no significant differentiation among years, sexes or stage-classes at the Refuge. Understanding the distribution of this foraging population advances knowledge of green turtles and contributes to effective conservation planning for this threatened species.