Green turtles, Chelonia mydas, are among the most ecologically important marine megafauna on the planet. Adult turtles graze on seagrass meadows, keeping these underwater pastures healthy, while the animals themselves serve as prey, hosts, competitors and even apex predators within marine food webs. Seven species of sea turtles exist worldwide, and Malaysia hosts nesting by five of them, including the green turtle, known locally as penyu agar or penyu hijau. The species is the most widely distributed sea turtle in the country, with nesting recorded in Sabah, Sarawak, Terengganu, Perak, Pahang and Johor. At the well-known Sabah Turtle Islands, annual nest counts can reach 15,000, and Redang Island records between 700 and 1,500 nests each year.

Similajau National Park tells a very different story. Gazetted in 1976 and spanning 89.96 square kilometers, the park protects golden sandy beaches, mixed dipterocarp forests and kerangas woodlands, along with endemic primates such as the Bornean banded langur and Hose’s surili. Its four main nesting beaches, Chalet Beach, Turtle Beach 1, Turtle Beach 2 and Golden Beach, have never received the scientific attention lavished on Sarawak’s flagship rookeries like Talang-Satang National Park. Records kept by rangers of the Sarawak Forestry Corporation, who patrol the high tide lines looking for flipper tracks, formed the raw material for the new analysis, which covered the years 2015 to 2017 and 2022 to 2024. Years with missing records, including 2018 and the pandemic closure period of 2019 to 2021, were deliberately excluded to avoid mistaking absent data for absent turtles.

The headline numbers are stark. Across the study years, nesting activity was low and inconsistent, averaging just 3.33 nests per year, with annual totals ranging from zero to six. In 2023, despite routine patrols, no green turtle nesting was confirmed at all. The mean hatching success rate across the study period was 45.47 percent, swinging from a low of 24 percent in 2016 to a high of 90 percent in 2022. For comparison, Talang-Satang National Park records more than 2,000 nests annually, Redang Island up to 2,500, and the Sabah Turtle Islands as many as 15,000. Against those benchmarks, Similajau is a footnote in Malaysian sea turtle reproduction, but a footnote that conservationists cannot afford to ignore.

The year 2024 offered the most detailed window into the park’s reproductive biology, because that was the first year clutch-level data were recorded. Four nests on Chalet Beach were discovered and successfully relocated to the park’s roofed, fenced and elevated hatchery. Clutch sizes ranged from 119 to 137 eggs, averaging 129.75 eggs, a figure that sits comfortably within the range reported for green turtles elsewhere in Malaysia and beyond, such as 42 to 150 eggs per clutch in Negeri Sembilan and 74 to 179 in the Chagos Archipelago. Because clutch size generally correlates with female body size, the authors suggest, cautiously, that the females nesting at Similajau may be relatively large, older remigrant individuals, though no tagging or morphometric data were available to confirm this.

The fate of those four nests revealed how precarious reproduction is at the site. Apparent incubation durations ranged from 54 to 62 days, averaging 58.5 days, which is comparable to the roughly 60-day incubation period typical of sea turtles and hints that nest temperatures probably fell within a generally suitable range. But hatching success varied enormously, from a catastrophic 7.69 percent in the first nest to 73.11 percent in the fourth, averaging 41.8 percent with a standard deviation of 26.8. The first nest had been inundated by seawater before it was relocated, and its detection came up to five days after oviposition because of a patrol gap. When researchers excavated the nests after emergence, approximately 95 percent of the unhatched eggs showed no embryonic development at all, a pattern consistent with early mortality caused by flooding, osmotic stress and reduced oxygen availability in waterlogged sand.

Nest relocation itself is a double-edged sword. Moving eggs is standard practice when in-situ nests face near-certain destruction from predators, tidal flooding or human disturbance, and at Similajau the threats are real: ghost crabs, macaques, feral pigs, monitor lizards, ants and fungal infections are all documented in Malaysia and present in the park. But timing matters enormously. Relocation is ideally performed within one to two hours of oviposition, before the yolk sac membrane attaches to the shell, and although it can be done within 12 hours, hatching success declines significantly. At Similajau, remote beaches and irregular patrol coverage mean nests are often found too late for optimal handling, and broken eggs during relocation, six in one nest and nine in another in 2024, further eroded output. The study also notes that a metal pole used to locate eggs within nest pits can break eggs at the top of the clutch.

The 2024 season also exposed the difficulty of simply counting what happens on the beach. Rangers detected 20 nest pits that year, but only four could be confirmed as successful nests with eggs. Five pits were surrounded by scattered predated eggshell remnants, evidence that eggs had been laid and then eaten, while the remaining 11 showed no clear evidence of oviposition and may have been abandoned nesting attempts. Because the pits were clustered close together, it was impossible to determine whether the eggshell fragments represented separate nesting events or the remains of a single clutch dragged apart by wildlife, rain or tides. The authors argue that estimating true nest numbers from eggshell fragments alone is unreliable on beaches inhabited by diverse fauna and continually reshaped by waves and sediment movement.

Why is Similajau so quiet compared with other Malaysian rookeries? The study points to a possible historical legacy: mass mortality events in the 1990s, when roughly 100 sea turtle carcasses were recorded annually along Sarawak’s coasts, largely attributed to illegal trawling in key foraging areas, migratory routes and inter-nesting habitats. Given how far green turtles roam across Sarawak waters, the turtles that once nested at Similajau may have been caught up in those losses. Ongoing pressures compound the problem, from habitat degradation, climate change, egg and meat poaching, fisheries bycatch and ghost nets to unsustainable tourism, marine debris entanglement and vessel strikes. Because green turtles mature late and live long, any recovery in nesting activity will be slow and will require sustained intervention.

The researchers are careful about the limits of their work. The dataset is small and fragmented, patrol coverage varied from daily monitoring on Chalet Beach to monthly visits elsewhere, and records of survey effort over the years were unavailable, so the true nesting frequency could be higher than the counts suggest. No incubation temperatures were recorded, fungal infection of unhatched eggs was not examined, and the emergence success of hatchlings was never measured, though supervised releases mean it probably resembled hatching success. What the study delivers instead is a baseline, the first quantitative characterization of a nesting population that had previously gone unmeasured. The authors recommend intensified patrols during peak nesting periods, faster relocation to minimize embryo mortality, possible in-situ protection with predator exclusion or shading for low-risk nests, expanded surveys of nearby beaches, and community-based monitoring involving local stakeholders, conservation groups and university volunteers. They also call for research into the environmental drivers of reproductive output, including temperature, humidity and microbial infection. The reappearance of nesting at Similajau since 2015 is encouraging, they conclude, but the low and inconsistent numbers make clear that this quiet corner of Borneo will need decades of attention if its green turtles are to endure.

Subject of Research: Green turtle nesting activity and reproductive output at Similajau National Park, Sarawak

Article Title: Nesting activity and reproductive output of green turtles in Similajau National Park, Bintulu, Sarawak

Article References: Ting Jia Lei, A., & Hassan, R. B. (2026). Nesting activity and reproductive output of green turtles in Similajau National Park, Bintulu, Sarawak. Frontiers in Amphibian and Reptile Science, 4, Article 1890215. https://doi.org/10.3389/famrs.2026.1890215

Image Credits: AI Generated

DOI: 10.3389/famrs.2026.1890215

Keywords: green turtle, Chelonia mydas, Similajau National Park, Sarawak, nesting activity, hatching success, nest relocation, embryo mortality, sea turtle conservation, Malaysia, marine megafauna, hatchery management

Amphibians are already the most threatened class of vertebrates on Earth, with habitat loss, disease, pollution, and climate change combining to push hundreds of species toward extinction. Because amphibians have permeable skin and eggs that develop directly in water, they are acutely sensitive to shifts in environmental temperature. The research team, led by Jiahui Zhang and corresponding author Zhangmin Yang of Shaanxi Normal University in Xi’an, China, set out to answer a question that has received surprisingly little attention: does high temperature affect not only how fast amphibian embryos develop, but also which microbes take up residence in their guts as that development proceeds?

The experimental design was straightforward but rigorous. The researchers divided Bufo gargarizans embryos into two groups: a control group maintained at normal temperatures and a high-temperature group exposed to elevated thermal conditions. They then tracked the embryos through every stage of development, from fertilization through hatching, recording the total time required for complete embryonic development, the proportion of embryos that hatched successfully, and the proportion that emerged with malformations. To characterize the gut microbial communities, the team employed 16S rRNA sequencing, a technique that reads a specific genetic marker found in bacteria and allows scientists to identify which microbial taxa are present and in what relative abundances.

The developmental results were striking. Embryos in the control group required 502.04 hours to complete development, while those in the high-temperature group finished in just 214.04 hours — a dramatic acceleration of more than half the normal developmental period. The effect was especially pronounced during the organogenesis stage, the critical window in which the embryo’s organs and body systems are being formed. On the surface, faster development might sound like an advantage, a way for embryos to escape vulnerable aquatic eggs more quickly. But the study’s other metrics told a more troubling story.

Embryos raised under high-temperature conditions showed significantly lower hatching success and significantly higher rates of malformation compared with controls, differences that were statistically significant at the P<0.05 threshold. In other words, the speed came at a cost. Rapid development driven by heat appears to compromise the quality of the outcome, producing fewer viable hatchlings and more individuals with developmental defects. For wild populations facing increasingly frequent extreme heat events in their breeding ponds and streams, this trade-off could translate into reduced recruitment — fewer young toads surviving to join the adult population year after year.

The most novel contribution of the study, however, lies in its analysis of gut microbial colonization. The researchers found that high-temperature exposure fundamentally altered the profile of microbes establishing themselves in the embryonic gut. Specifically, the high-temperature group exhibited lower microbial richness, as measured by the Ace index, and lower microbial diversity, as measured by the Shannon index. Both metrics are standard tools in microbial ecology: richness counts how many different types of microbes are present, while diversity accounts for both the number of types and how evenly individuals are distributed among them. A reduction in both suggests a gut microbial community that is less complex and potentially less resilient.

The compositional shifts were equally telling. In the high-temperature group, the researchers documented elevated relative abundances of bacteria from the families Shewanellaceae, including the genus Shewanella; Aeromonadaceae, including the genus Aeromonas; and Bacteroidaceae, including the genus Bacteroides. By contrast, embryos in the control group showed marked enrichment of bacteria from the order Pseudomonadales, including the family Pseudomonadaceae and the genus Pseudomonas. These taxonomic differences, also significant at P<0.05, indicate that temperature is not merely nudging the microbial community around the margins but is actively selecting for a different cast of microbial characters during colonization.

Why does this matter? The gut microbiota of amphibians, as in other animals, plays a crucial role in nutrient processing, immune system training, and protection against pathogens. Some of the taxa enriched under high temperature, such as Aeromonas, are noteworthy because certain members of this genus are known opportunistic pathogens in aquatic animals, although the study did not directly assess pathogenicity in the toad embryos. The loss of microbial diversity during the earliest stages of gut colonization could deprive developing amphibians of functions they would normally acquire from a richer community, with consequences that might persist into later life stages. Because gut microbial colonization in embryos represents the founding event for the animal’s lifelong microbiome, disruptions at this stage may have cascading effects that are difficult to reverse.

The study also carries broader implications for how scientists assess the biological impacts of climate change. Much of the existing research on warming and amphibians has focused on physiological stress, range shifts, and disease dynamics, particularly the devastating effects of the chytrid fungus. This work adds a new dimension by demonstrating that thermal stress reaches all the way into the symbiotic relationships forming inside a developing embryo. The authors suggest that their findings can be placed in the broader context of climate change to explore the consequences of global warming for amphibians, providing a framework for assessing how extreme heat shapes both development and microbial colonization across other amphibian species.

For conservation biologists, the message is sobering. Extreme heat events are projected to increase in both frequency and intensity, and the breeding windows of many amphibians coincide with the warmest parts of the year. If high temperatures routinely accelerate development at the cost of hatching success and normal morphology, while simultaneously stripping diversity from the founding gut microbiome, then even populations that appear to be reproducing successfully may be quietly accumulating hidden deficits. The Bufo gargarizans embryos in this study developed roughly twice as fast under heat stress, yet paid for that speed with more malformations, fewer successful hatchings, and a simplified gut microbial community. As the authors and their colleagues at Shaanxi Normal University, supported by the Natural Science Foundation of Shaanxi Province, continue to investigate these dynamics, their work underscores a growing recognition in ecology: to understand how organisms will fare in a warming world, we must look not only at the animals themselves, but at the microscopic partners that help make them whole.

Subject of Research: Effects of high temperature on embryonic development and gut microbial colonization in the toad Bufo gargarizans

Article Title: Effects of High Temperature on Embryonic Development and Gut Microbial Colonization of Bufo gargarizans

Article References: Zhang, J., Peng, J., Wang, D., Li, W., Cao, X., Wang, H., & Yang, Z. (2026). Effects of High Temperature on Embryonic Development and Gut Microbial Colonization of Bufo gargarizans. Microbial Ecology. https://doi.org/10.1007/s00248-026-02893-1

Image Credits: AI Generated

DOI: 10.1007/s00248-026-02893-1

Keywords: amphibians, Bufo gargarizans, embryonic development, gut microbiota, microbial colonization, thermal stress, 16S rRNA sequencing, climate change, global warming, microbial ecology, organogenesis, hatching success

The study, published in the journal Discover Conservation, monitored seven olive ridley nests during the 2020–2021 nesting season, which runs from September through January in Ghana. Researchers led by Baidoo Abigail, Addo Samuel, and Agyekumhene Andrews deployed miniature HOBO U22 temperature data loggers directly into egg clutches as females were laying, positioning the devices near the center of the clutch where metabolic heat accumulates most. A second logger was buried roughly two meters from each nest at identical depth, acting as a control that recorded the background temperature of the surrounding beach sand. Both loggers recorded measurements every fifteen minutes for the entire incubation period, generating an unusually high-resolution record of the thermal environment experienced by developing embryos.

The most striking result concerns the moment when nest and sand temperatures part ways. For the first nineteen days of incubation, temperatures inside the eggs and in the adjacent sand tracked each other closely, with no statistically significant difference between them. But from day twenty onward—the period that coincides with the thermosensitive window during which hatchling sex is determined—nest temperatures rose consistently above sand temperatures and stayed elevated until the hatchlings emerged. The researchers attribute this divergence to metabolic heating: as embryos grow, their collective metabolic activity generates heat that warms the clutch from within, a phenomenon well documented in sea turtles but never before quantified at this West African site.

The numbers reveal how warm this rookery already runs. Mean nest temperatures across the seven nests ranged from 30.7 to 33.3 degrees Celsius, averaging 32.4 degrees, while adjacent sand temperatures averaged a cooler 31.7 degrees. When nest and sand temperatures diverged, the difference typically spanned 0.3 to 1.7 degrees Celsius, averaging about 0.9 degrees. These figures matter enormously because olive ridley turtles exhibit temperature-dependent sex determination: pivotal temperatures that produce equal numbers of males and females have been reported near 30.0 to 30.5 degrees Celsius, with anything warmer producing females. Since mean nest temperatures during the middle third of incubation—the critical sex-determining window—ranged from 31.5 to 32.9 degrees, the researchers conclude that the monitored nests exceeded pivotal thresholds for a substantial portion of development, strongly implying a female-biased hatchling output. Although sex ratios were not measured directly, the thermal signature alone is telling.

Temperature exerted its clearest influence on the pace of development. Incubation duration ranged from 45 to 57 days across the seven nests, averaging about 48 days, and was strongly and negatively correlated with mean nest temperature, with a correlation coefficient of minus 0.88. Warmer nests hatched markedly sooner, and mean nest temperature explained roughly 78 percent of the variation in incubation duration among nests. This relationship is among the most robust in reptilian developmental biology, but its confirmation in Ghanaian sands underscores how powerfully thermal conditions govern the timeline from egg to emergence, even across a modest sample of nests.

Perhaps surprisingly, temperature told a much weaker story about reproductive success itself. Hatching success ranged widely, from 53.4 to 95.5 percent, with a mean of 81 percent, and emergence success ranged from 44.3 to 92.9 percent, averaging 75.2 percent. Yet neither measure showed a meaningful correlation with mean nest temperature, and incubation duration likewise bore no relationship to success rates. The authors interpret this variability as evidence that factors beyond temperature—sand moisture, gas exchange within the nest chamber, beach compaction, and disturbance—interact in complex ways to determine whether embryos survive. The finding is a caution against attributing nest outcomes to temperature alone, particularly in natural environments where multiple stressors overlap.

The hatchlings themselves offered additional clues about thermal stress. Morphological abnormalities, most frequently non-uniform carapace development, were observed in hatchlings from nests with mean temperatures ranging from 32.6 to 33.2 degrees Celsius, and the two hottest nests, averaging 33.0 and 33.2 degrees, produced the greatest number of anomalies. Locomotor performance, assessed through a self-righting test in which hatchlings were placed upside down on moist sand and timed as they flipped themselves upright, showed a moderate association with nest temperature, though the relationship did not reach statistical significance in the small sample. Such performance traits are closely linked to post-emergence survival, since hatchlings that cannot right themselves or crawl quickly are more vulnerable to predators on their frantic dash to the sea.

The study also carries practical implications for how scientists model the future of sea turtle populations under climate change. Many recent studies estimate nest temperatures from sand temperature data by adding a correction—typically 0.5 to 1.0 degrees Celsius—to account for metabolic heating. The Ghanaian measurements, showing an average nest-to-sand difference of about 0.9 degrees during divergence, provide direct empirical support for the magnitude of such corrections at a tropical site where incubation temperatures already press against pivotal thresholds. The researchers note that the beach at Songor was artificially nourished in 2010 as part of coastal erosion mitigation, a process known elsewhere to alter sand thermal properties, though sediment characteristics were beyond the scope of this study. With global climate change projected to raise sand temperatures further, and with local coastal development reshaping nesting microclimates, accurate in-nest measurements will become ever more critical for forecasting sex ratios and hatchling survival.

The work is not without limitations. Seven nests constitute a small sample, spanning a single nesting season, and the statistical power to detect subtle relationships was correspondingly limited; tendencies toward cooler deeper nests and warmer larger clutches matched published patterns but did not reach significance. Fine-scale thermal gradients within clutches were not assessed, and hatchling sex was never directly determined. Still, as the authors emphasize, this study delivers the first baseline characterization of olive ridley nest thermal dynamics anywhere in West Africa, filling a conspicuous geographic gap in global sea turtle science. As temperatures continue to climb at nesting beaches worldwide, understanding precisely what developing embryos experience inside their eggs—not just what the surrounding sand feels like—may prove decisive for conserving one of the ocean’s most vulnerable travelers, and for ensuring that Ghana’s beaches keep producing hatchlings capable of completing their ancient journey back to the sea.

Subject of Research: Effects of incubation temperature on olive ridley sea turtle nest success and hatchling development at the Songor Ramsar Site, Ghana

Article Title: Effects of incubation temperature on olive ridley sea turtle nest success at the Songor Ramsar Site, Ghana

Article References: Abigail, B., Samuel, A., & Andrews, A. (2026). Effects of incubation temperature on olive ridley sea turtle nest success at the Songor Ramsar Site, Ghana. Discover Conservation, 3(1), Article 40. https://doi.org/10.1007/s44353-026-00109-8

Image Credits: AI Generated

DOI: 10.1007/s44353-026-00109-8

Keywords: olive ridley sea turtle, incubation temperature, metabolic heating, temperature-dependent sex determination, hatching success, Songor Ramsar Site, Ghana, climate change, nest temperature, hatchling performance, West Africa, conservation